The following commit has been merged into the locking/core branch of tip:
Commit-ID: 85dc28fa4ec058645c29bda952d901b29dfaa0b0
Gitweb: https://git.kernel.org/tip/85dc28fa4ec058645c29bda952d901b29dfaa0b0
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 23 Sep 2021 14:10:58 -03:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 07 Oct 2021 13:51:09 +02:00
futex: Split out PI futex
Move the PI futex implementation into it's own file.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: André Almeida <andrealmeid@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210923171111.300673-10-andrealmeid@xxxxxxxxxxxxx
---
kernel/futex/Makefile | 2 +-
kernel/futex/core.c | 1508 ++--------------------------------------
kernel/futex/futex.h | 117 +++-
kernel/futex/pi.c | 1233 +++++++++++++++++++++++++++++++++-
4 files changed, 1452 insertions(+), 1408 deletions(-)
create mode 100644 kernel/futex/pi.c
diff --git a/kernel/futex/Makefile b/kernel/futex/Makefile
index ff9a960..27b71c2 100644
--- a/kernel/futex/Makefile
+++ b/kernel/futex/Makefile
@@ -1,3 +1,3 @@
# SPDX-License-Identifier: GPL-2.0
-obj-y += core.o syscalls.o
+obj-y += core.o syscalls.o pi.o
diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index 0e10aee..a8ca5b5 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -148,67 +148,6 @@ int __read_mostly futex_cmpxchg_enabled;
/*
- * Priority Inheritance state:
- */
-struct futex_pi_state {
- /*
- * list of 'owned' pi_state instances - these have to be
- * cleaned up in do_exit() if the task exits prematurely:
- */
- struct list_head list;
-
- /*
- * The PI object:
- */
- struct rt_mutex_base pi_mutex;
-
- struct task_struct *owner;
- refcount_t refcount;
-
- union futex_key key;
-} __randomize_layout;
-
-/**
- * struct futex_q - The hashed futex queue entry, one per waiting task
- * @list: priority-sorted list of tasks waiting on this futex
- * @task: the task waiting on the futex
- * @lock_ptr: the hash bucket lock
- * @key: the key the futex is hashed on
- * @pi_state: optional priority inheritance state
- * @rt_waiter: rt_waiter storage for use with requeue_pi
- * @requeue_pi_key: the requeue_pi target futex key
- * @bitset: bitset for the optional bitmasked wakeup
- * @requeue_state: State field for futex_requeue_pi()
- * @requeue_wait: RCU wait for futex_requeue_pi() (RT only)
- *
- * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so
- * we can wake only the relevant ones (hashed queues may be shared).
- *
- * A futex_q has a woken state, just like tasks have TASK_RUNNING.
- * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
- * The order of wakeup is always to make the first condition true, then
- * the second.
- *
- * PI futexes are typically woken before they are removed from the hash list via
- * the rt_mutex code. See futex_unqueue_pi().
- */
-struct futex_q {
- struct plist_node list;
-
- struct task_struct *task;
- spinlock_t *lock_ptr;
- union futex_key key;
- struct futex_pi_state *pi_state;
- struct rt_mutex_waiter *rt_waiter;
- union futex_key *requeue_pi_key;
- u32 bitset;
- atomic_t requeue_state;
-#ifdef CONFIG_PREEMPT_RT
- struct rcuwait requeue_wait;
-#endif
-} __randomize_layout;
-
-/*
* On PREEMPT_RT, the hash bucket lock is a 'sleeping' spinlock with an
* underlying rtmutex. The task which is about to be requeued could have
* just woken up (timeout, signal). After the wake up the task has to
@@ -259,7 +198,7 @@ enum {
Q_REQUEUE_PI_LOCKED,
};
-static const struct futex_q futex_q_init = {
+const struct futex_q futex_q_init = {
/* list gets initialized in futex_queue()*/
.key = FUTEX_KEY_INIT,
.bitset = FUTEX_BITSET_MATCH_ANY,
@@ -267,17 +206,6 @@ static const struct futex_q futex_q_init = {
};
/*
- * Hash buckets are shared by all the futex_keys that hash to the same
- * location. Each key may have multiple futex_q structures, one for each task
- * waiting on a futex.
- */
-struct futex_hash_bucket {
- atomic_t waiters;
- spinlock_t lock;
- struct plist_head chain;
-} ____cacheline_aligned_in_smp;
-
-/*
* The base of the bucket array and its size are always used together
* (after initialization only in futex_hash()), so ensure that they
* reside in the same cacheline.
@@ -386,7 +314,7 @@ static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
* We hash on the keys returned from get_futex_key (see below) and return the
* corresponding hash bucket in the global hash.
*/
-static struct futex_hash_bucket *futex_hash(union futex_key *key)
+struct futex_hash_bucket *futex_hash(union futex_key *key)
{
u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
key->both.offset);
@@ -410,11 +338,6 @@ static inline int match_futex(union futex_key *key1, union futex_key *key2)
&& key1->both.offset == key2->both.offset);
}
-enum futex_access {
- FUTEX_READ,
- FUTEX_WRITE
-};
-
/**
* futex_setup_timer - set up the sleeping hrtimer.
* @time: ptr to the given timeout value
@@ -425,7 +348,7 @@ enum futex_access {
* Return: Initialized hrtimer_sleeper structure or NULL if no timeout
* value given
*/
-static inline struct hrtimer_sleeper *
+struct hrtimer_sleeper *
futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout,
int flags, u64 range_ns)
{
@@ -511,8 +434,8 @@ static u64 get_inode_sequence_number(struct inode *inode)
*
* lock_page() might sleep, the caller should not hold a spinlock.
*/
-static int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key,
- enum futex_access rw)
+int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key,
+ enum futex_access rw)
{
unsigned long address = (unsigned long)uaddr;
struct mm_struct *mm = current->mm;
@@ -700,7 +623,7 @@ out:
* disabled section so we can as well avoid the #PF overhead by
* calling get_user_pages() right away.
*/
-static int fault_in_user_writeable(u32 __user *uaddr)
+int fault_in_user_writeable(u32 __user *uaddr)
{
struct mm_struct *mm = current->mm;
int ret;
@@ -720,8 +643,7 @@ static int fault_in_user_writeable(u32 __user *uaddr)
*
* Must be called with the hb lock held.
*/
-static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
- union futex_key *key)
+struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb, union futex_key *key)
{
struct futex_q *this;
@@ -732,8 +654,7 @@ static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
return NULL;
}
-static int futex_cmpxchg_value_locked(u32 *curval, u32 __user *uaddr,
- u32 uval, u32 newval)
+int futex_cmpxchg_value_locked(u32 *curval, u32 __user *uaddr, u32 uval, u32 newval)
{
int ret;
@@ -744,7 +665,7 @@ static int futex_cmpxchg_value_locked(u32 *curval, u32 __user *uaddr,
return ret;
}
-static int futex_get_value_locked(u32 *dest, u32 __user *from)
+int futex_get_value_locked(u32 *dest, u32 __user *from)
{
int ret;
@@ -755,399 +676,6 @@ static int futex_get_value_locked(u32 *dest, u32 __user *from)
return ret ? -EFAULT : 0;
}
-
-/*
- * PI code:
- */
-static int refill_pi_state_cache(void)
-{
- struct futex_pi_state *pi_state;
-
- if (likely(current->pi_state_cache))
- return 0;
-
- pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
-
- if (!pi_state)
- return -ENOMEM;
-
- INIT_LIST_HEAD(&pi_state->list);
- /* pi_mutex gets initialized later */
- pi_state->owner = NULL;
- refcount_set(&pi_state->refcount, 1);
- pi_state->key = FUTEX_KEY_INIT;
-
- current->pi_state_cache = pi_state;
-
- return 0;
-}
-
-static struct futex_pi_state *alloc_pi_state(void)
-{
- struct futex_pi_state *pi_state = current->pi_state_cache;
-
- WARN_ON(!pi_state);
- current->pi_state_cache = NULL;
-
- return pi_state;
-}
-
-static void pi_state_update_owner(struct futex_pi_state *pi_state,
- struct task_struct *new_owner)
-{
- struct task_struct *old_owner = pi_state->owner;
-
- lockdep_assert_held(&pi_state->pi_mutex.wait_lock);
-
- if (old_owner) {
- raw_spin_lock(&old_owner->pi_lock);
- WARN_ON(list_empty(&pi_state->list));
- list_del_init(&pi_state->list);
- raw_spin_unlock(&old_owner->pi_lock);
- }
-
- if (new_owner) {
- raw_spin_lock(&new_owner->pi_lock);
- WARN_ON(!list_empty(&pi_state->list));
- list_add(&pi_state->list, &new_owner->pi_state_list);
- pi_state->owner = new_owner;
- raw_spin_unlock(&new_owner->pi_lock);
- }
-}
-
-static void get_pi_state(struct futex_pi_state *pi_state)
-{
- WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
-}
-
-/*
- * Drops a reference to the pi_state object and frees or caches it
- * when the last reference is gone.
- */
-static void put_pi_state(struct futex_pi_state *pi_state)
-{
- if (!pi_state)
- return;
-
- if (!refcount_dec_and_test(&pi_state->refcount))
- return;
-
- /*
- * If pi_state->owner is NULL, the owner is most probably dying
- * and has cleaned up the pi_state already
- */
- if (pi_state->owner) {
- unsigned long flags;
-
- raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
- pi_state_update_owner(pi_state, NULL);
- rt_mutex_proxy_unlock(&pi_state->pi_mutex);
- raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
- }
-
- if (current->pi_state_cache) {
- kfree(pi_state);
- } else {
- /*
- * pi_state->list is already empty.
- * clear pi_state->owner.
- * refcount is at 0 - put it back to 1.
- */
- pi_state->owner = NULL;
- refcount_set(&pi_state->refcount, 1);
- current->pi_state_cache = pi_state;
- }
-}
-
-#ifdef CONFIG_FUTEX_PI
-
-/*
- * This task is holding PI mutexes at exit time => bad.
- * Kernel cleans up PI-state, but userspace is likely hosed.
- * (Robust-futex cleanup is separate and might save the day for userspace.)
- */
-static void exit_pi_state_list(struct task_struct *curr)
-{
- struct list_head *next, *head = &curr->pi_state_list;
- struct futex_pi_state *pi_state;
- struct futex_hash_bucket *hb;
- union futex_key key = FUTEX_KEY_INIT;
-
- if (!futex_cmpxchg_enabled)
- return;
- /*
- * We are a ZOMBIE and nobody can enqueue itself on
- * pi_state_list anymore, but we have to be careful
- * versus waiters unqueueing themselves:
- */
- raw_spin_lock_irq(&curr->pi_lock);
- while (!list_empty(head)) {
- next = head->next;
- pi_state = list_entry(next, struct futex_pi_state, list);
- key = pi_state->key;
- hb = futex_hash(&key);
-
- /*
- * We can race against put_pi_state() removing itself from the
- * list (a waiter going away). put_pi_state() will first
- * decrement the reference count and then modify the list, so
- * its possible to see the list entry but fail this reference
- * acquire.
- *
- * In that case; drop the locks to let put_pi_state() make
- * progress and retry the loop.
- */
- if (!refcount_inc_not_zero(&pi_state->refcount)) {
- raw_spin_unlock_irq(&curr->pi_lock);
- cpu_relax();
- raw_spin_lock_irq(&curr->pi_lock);
- continue;
- }
- raw_spin_unlock_irq(&curr->pi_lock);
-
- spin_lock(&hb->lock);
- raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
- raw_spin_lock(&curr->pi_lock);
- /*
- * We dropped the pi-lock, so re-check whether this
- * task still owns the PI-state:
- */
- if (head->next != next) {
- /* retain curr->pi_lock for the loop invariant */
- raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
- spin_unlock(&hb->lock);
- put_pi_state(pi_state);
- continue;
- }
-
- WARN_ON(pi_state->owner != curr);
- WARN_ON(list_empty(&pi_state->list));
- list_del_init(&pi_state->list);
- pi_state->owner = NULL;
-
- raw_spin_unlock(&curr->pi_lock);
- raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
- spin_unlock(&hb->lock);
-
- rt_mutex_futex_unlock(&pi_state->pi_mutex);
- put_pi_state(pi_state);
-
- raw_spin_lock_irq(&curr->pi_lock);
- }
- raw_spin_unlock_irq(&curr->pi_lock);
-}
-#else
-static inline void exit_pi_state_list(struct task_struct *curr) { }
-#endif
-
-/*
- * We need to check the following states:
- *
- * Waiter | pi_state | pi->owner | uTID | uODIED | ?
- *
- * [1] NULL | --- | --- | 0 | 0/1 | Valid
- * [2] NULL | --- | --- | >0 | 0/1 | Valid
- *
- * [3] Found | NULL | -- | Any | 0/1 | Invalid
- *
- * [4] Found | Found | NULL | 0 | 1 | Valid
- * [5] Found | Found | NULL | >0 | 1 | Invalid
- *
- * [6] Found | Found | task | 0 | 1 | Valid
- *
- * [7] Found | Found | NULL | Any | 0 | Invalid
- *
- * [8] Found | Found | task | ==taskTID | 0/1 | Valid
- * [9] Found | Found | task | 0 | 0 | Invalid
- * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
- *
- * [1] Indicates that the kernel can acquire the futex atomically. We
- * came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
- *
- * [2] Valid, if TID does not belong to a kernel thread. If no matching
- * thread is found then it indicates that the owner TID has died.
- *
- * [3] Invalid. The waiter is queued on a non PI futex
- *
- * [4] Valid state after exit_robust_list(), which sets the user space
- * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
- *
- * [5] The user space value got manipulated between exit_robust_list()
- * and exit_pi_state_list()
- *
- * [6] Valid state after exit_pi_state_list() which sets the new owner in
- * the pi_state but cannot access the user space value.
- *
- * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
- *
- * [8] Owner and user space value match
- *
- * [9] There is no transient state which sets the user space TID to 0
- * except exit_robust_list(), but this is indicated by the
- * FUTEX_OWNER_DIED bit. See [4]
- *
- * [10] There is no transient state which leaves owner and user space
- * TID out of sync. Except one error case where the kernel is denied
- * write access to the user address, see fixup_pi_state_owner().
- *
- *
- * Serialization and lifetime rules:
- *
- * hb->lock:
- *
- * hb -> futex_q, relation
- * futex_q -> pi_state, relation
- *
- * (cannot be raw because hb can contain arbitrary amount
- * of futex_q's)
- *
- * pi_mutex->wait_lock:
- *
- * {uval, pi_state}
- *
- * (and pi_mutex 'obviously')
- *
- * p->pi_lock:
- *
- * p->pi_state_list -> pi_state->list, relation
- * pi_mutex->owner -> pi_state->owner, relation
- *
- * pi_state->refcount:
- *
- * pi_state lifetime
- *
- *
- * Lock order:
- *
- * hb->lock
- * pi_mutex->wait_lock
- * p->pi_lock
- *
- */
-
-/*
- * Validate that the existing waiter has a pi_state and sanity check
- * the pi_state against the user space value. If correct, attach to
- * it.
- */
-static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
- struct futex_pi_state *pi_state,
- struct futex_pi_state **ps)
-{
- pid_t pid = uval & FUTEX_TID_MASK;
- u32 uval2;
- int ret;
-
- /*
- * Userspace might have messed up non-PI and PI futexes [3]
- */
- if (unlikely(!pi_state))
- return -EINVAL;
-
- /*
- * We get here with hb->lock held, and having found a
- * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
- * has dropped the hb->lock in between futex_queue() and futex_unqueue_pi(),
- * which in turn means that futex_lock_pi() still has a reference on
- * our pi_state.
- *
- * The waiter holding a reference on @pi_state also protects against
- * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
- * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
- * free pi_state before we can take a reference ourselves.
- */
- WARN_ON(!refcount_read(&pi_state->refcount));
-
- /*
- * Now that we have a pi_state, we can acquire wait_lock
- * and do the state validation.
- */
- raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
-
- /*
- * Since {uval, pi_state} is serialized by wait_lock, and our current
- * uval was read without holding it, it can have changed. Verify it
- * still is what we expect it to be, otherwise retry the entire
- * operation.
- */
- if (futex_get_value_locked(&uval2, uaddr))
- goto out_efault;
-
- if (uval != uval2)
- goto out_eagain;
-
- /*
- * Handle the owner died case:
- */
- if (uval & FUTEX_OWNER_DIED) {
- /*
- * exit_pi_state_list sets owner to NULL and wakes the
- * topmost waiter. The task which acquires the
- * pi_state->rt_mutex will fixup owner.
- */
- if (!pi_state->owner) {
- /*
- * No pi state owner, but the user space TID
- * is not 0. Inconsistent state. [5]
- */
- if (pid)
- goto out_einval;
- /*
- * Take a ref on the state and return success. [4]
- */
- goto out_attach;
- }
-
- /*
- * If TID is 0, then either the dying owner has not
- * yet executed exit_pi_state_list() or some waiter
- * acquired the rtmutex in the pi state, but did not
- * yet fixup the TID in user space.
- *
- * Take a ref on the state and return success. [6]
- */
- if (!pid)
- goto out_attach;
- } else {
- /*
- * If the owner died bit is not set, then the pi_state
- * must have an owner. [7]
- */
- if (!pi_state->owner)
- goto out_einval;
- }
-
- /*
- * Bail out if user space manipulated the futex value. If pi
- * state exists then the owner TID must be the same as the
- * user space TID. [9/10]
- */
- if (pid != task_pid_vnr(pi_state->owner))
- goto out_einval;
-
-out_attach:
- get_pi_state(pi_state);
- raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
- *ps = pi_state;
- return 0;
-
-out_einval:
- ret = -EINVAL;
- goto out_error;
-
-out_eagain:
- ret = -EAGAIN;
- goto out_error;
-
-out_efault:
- ret = -EFAULT;
- goto out_error;
-
-out_error:
- raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
- return ret;
-}
-
/**
* wait_for_owner_exiting - Block until the owner has exited
* @ret: owner's current futex lock status
@@ -1155,7 +683,7 @@ out_error:
*
* Caller must hold a refcount on @exiting.
*/
-static void wait_for_owner_exiting(int ret, struct task_struct *exiting)
+void wait_for_owner_exiting(int ret, struct task_struct *exiting)
{
if (ret != -EBUSY) {
WARN_ON_ONCE(exiting);
@@ -1179,296 +707,6 @@ static void wait_for_owner_exiting(int ret, struct task_struct *exiting)
put_task_struct(exiting);
}
-static int handle_exit_race(u32 __user *uaddr, u32 uval,
- struct task_struct *tsk)
-{
- u32 uval2;
-
- /*
- * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
- * caller that the alleged owner is busy.
- */
- if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
- return -EBUSY;
-
- /*
- * Reread the user space value to handle the following situation:
- *
- * CPU0 CPU1
- *
- * sys_exit() sys_futex()
- * do_exit() futex_lock_pi()
- * futex_lock_pi_atomic()
- * exit_signals(tsk) No waiters:
- * tsk->flags |= PF_EXITING; *uaddr == 0x00000PID
- * mm_release(tsk) Set waiter bit
- * exit_robust_list(tsk) { *uaddr = 0x80000PID;
- * Set owner died attach_to_pi_owner() {
- * *uaddr = 0xC0000000; tsk = get_task(PID);
- * } if (!tsk->flags & PF_EXITING) {
- * ... attach();
- * tsk->futex_state = } else {
- * FUTEX_STATE_DEAD; if (tsk->futex_state !=
- * FUTEX_STATE_DEAD)
- * return -EAGAIN;
- * return -ESRCH; <--- FAIL
- * }
- *
- * Returning ESRCH unconditionally is wrong here because the
- * user space value has been changed by the exiting task.
- *
- * The same logic applies to the case where the exiting task is
- * already gone.
- */
- if (futex_get_value_locked(&uval2, uaddr))
- return -EFAULT;
-
- /* If the user space value has changed, try again. */
- if (uval2 != uval)
- return -EAGAIN;
-
- /*
- * The exiting task did not have a robust list, the robust list was
- * corrupted or the user space value in *uaddr is simply bogus.
- * Give up and tell user space.
- */
- return -ESRCH;
-}
-
-static void __attach_to_pi_owner(struct task_struct *p, union futex_key *key,
- struct futex_pi_state **ps)
-{
- /*
- * No existing pi state. First waiter. [2]
- *
- * This creates pi_state, we have hb->lock held, this means nothing can
- * observe this state, wait_lock is irrelevant.
- */
- struct futex_pi_state *pi_state = alloc_pi_state();
-
- /*
- * Initialize the pi_mutex in locked state and make @p
- * the owner of it:
- */
- rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
-
- /* Store the key for possible exit cleanups: */
- pi_state->key = *key;
-
- WARN_ON(!list_empty(&pi_state->list));
- list_add(&pi_state->list, &p->pi_state_list);
- /*
- * Assignment without holding pi_state->pi_mutex.wait_lock is safe
- * because there is no concurrency as the object is not published yet.
- */
- pi_state->owner = p;
-
- *ps = pi_state;
-}
-/*
- * Lookup the task for the TID provided from user space and attach to
- * it after doing proper sanity checks.
- */
-static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key,
- struct futex_pi_state **ps,
- struct task_struct **exiting)
-{
- pid_t pid = uval & FUTEX_TID_MASK;
- struct task_struct *p;
-
- /*
- * We are the first waiter - try to look up the real owner and attach
- * the new pi_state to it, but bail out when TID = 0 [1]
- *
- * The !pid check is paranoid. None of the call sites should end up
- * with pid == 0, but better safe than sorry. Let the caller retry
- */
- if (!pid)
- return -EAGAIN;
- p = find_get_task_by_vpid(pid);
- if (!p)
- return handle_exit_race(uaddr, uval, NULL);
-
- if (unlikely(p->flags & PF_KTHREAD)) {
- put_task_struct(p);
- return -EPERM;
- }
-
- /*
- * We need to look at the task state to figure out, whether the
- * task is exiting. To protect against the change of the task state
- * in futex_exit_release(), we do this protected by p->pi_lock:
- */
- raw_spin_lock_irq(&p->pi_lock);
- if (unlikely(p->futex_state != FUTEX_STATE_OK)) {
- /*
- * The task is on the way out. When the futex state is
- * FUTEX_STATE_DEAD, we know that the task has finished
- * the cleanup:
- */
- int ret = handle_exit_race(uaddr, uval, p);
-
- raw_spin_unlock_irq(&p->pi_lock);
- /*
- * If the owner task is between FUTEX_STATE_EXITING and
- * FUTEX_STATE_DEAD then store the task pointer and keep
- * the reference on the task struct. The calling code will
- * drop all locks, wait for the task to reach
- * FUTEX_STATE_DEAD and then drop the refcount. This is
- * required to prevent a live lock when the current task
- * preempted the exiting task between the two states.
- */
- if (ret == -EBUSY)
- *exiting = p;
- else
- put_task_struct(p);
- return ret;
- }
-
- __attach_to_pi_owner(p, key, ps);
- raw_spin_unlock_irq(&p->pi_lock);
-
- put_task_struct(p);
-
- return 0;
-}
-
-static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
-{
- int err;
- u32 curval;
-
- if (unlikely(should_fail_futex(true)))
- return -EFAULT;
-
- err = futex_cmpxchg_value_locked(&curval, uaddr, uval, newval);
- if (unlikely(err))
- return err;
-
- /* If user space value changed, let the caller retry */
- return curval != uval ? -EAGAIN : 0;
-}
-
-/**
- * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
- * @uaddr: the pi futex user address
- * @hb: the pi futex hash bucket
- * @key: the futex key associated with uaddr and hb
- * @ps: the pi_state pointer where we store the result of the
- * lookup
- * @task: the task to perform the atomic lock work for. This will
- * be "current" except in the case of requeue pi.
- * @exiting: Pointer to store the task pointer of the owner task
- * which is in the middle of exiting
- * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
- *
- * Return:
- * - 0 - ready to wait;
- * - 1 - acquired the lock;
- * - <0 - error
- *
- * The hb->lock must be held by the caller.
- *
- * @exiting is only set when the return value is -EBUSY. If so, this holds
- * a refcount on the exiting task on return and the caller needs to drop it
- * after waiting for the exit to complete.
- */
-static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
- union futex_key *key,
- struct futex_pi_state **ps,
- struct task_struct *task,
- struct task_struct **exiting,
- int set_waiters)
-{
- u32 uval, newval, vpid = task_pid_vnr(task);
- struct futex_q *top_waiter;
- int ret;
-
- /*
- * Read the user space value first so we can validate a few
- * things before proceeding further.
- */
- if (futex_get_value_locked(&uval, uaddr))
- return -EFAULT;
-
- if (unlikely(should_fail_futex(true)))
- return -EFAULT;
-
- /*
- * Detect deadlocks.
- */
- if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
- return -EDEADLK;
-
- if ((unlikely(should_fail_futex(true))))
- return -EDEADLK;
-
- /*
- * Lookup existing state first. If it exists, try to attach to
- * its pi_state.
- */
- top_waiter = futex_top_waiter(hb, key);
- if (top_waiter)
- return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
-
- /*
- * No waiter and user TID is 0. We are here because the
- * waiters or the owner died bit is set or called from
- * requeue_cmp_pi or for whatever reason something took the
- * syscall.
- */
- if (!(uval & FUTEX_TID_MASK)) {
- /*
- * We take over the futex. No other waiters and the user space
- * TID is 0. We preserve the owner died bit.
- */
- newval = uval & FUTEX_OWNER_DIED;
- newval |= vpid;
-
- /* The futex requeue_pi code can enforce the waiters bit */
- if (set_waiters)
- newval |= FUTEX_WAITERS;
-
- ret = lock_pi_update_atomic(uaddr, uval, newval);
- if (ret)
- return ret;
-
- /*
- * If the waiter bit was requested the caller also needs PI
- * state attached to the new owner of the user space futex.
- *
- * @task is guaranteed to be alive and it cannot be exiting
- * because it is either sleeping or waiting in
- * futex_requeue_pi_wakeup_sync().
- *
- * No need to do the full attach_to_pi_owner() exercise
- * because @task is known and valid.
- */
- if (set_waiters) {
- raw_spin_lock_irq(&task->pi_lock);
- __attach_to_pi_owner(task, key, ps);
- raw_spin_unlock_irq(&task->pi_lock);
- }
- return 1;
- }
-
- /*
- * First waiter. Set the waiters bit before attaching ourself to
- * the owner. If owner tries to unlock, it will be forced into
- * the kernel and blocked on hb->lock.
- */
- newval = uval | FUTEX_WAITERS;
- ret = lock_pi_update_atomic(uaddr, uval, newval);
- if (ret)
- return ret;
- /*
- * If the update of the user space value succeeded, we try to
- * attach to the owner. If that fails, no harm done, we only
- * set the FUTEX_WAITERS bit in the user space variable.
- */
- return attach_to_pi_owner(uaddr, newval, key, ps, exiting);
-}
-
/**
* __futex_unqueue() - Remove the futex_q from its futex_hash_bucket
* @q: The futex_q to unqueue
@@ -1520,79 +758,6 @@ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
}
/*
- * Caller must hold a reference on @pi_state.
- */
-static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
-{
- struct rt_mutex_waiter *top_waiter;
- struct task_struct *new_owner;
- bool postunlock = false;
- DEFINE_RT_WAKE_Q(wqh);
- u32 curval, newval;
- int ret = 0;
-
- top_waiter = rt_mutex_top_waiter(&pi_state->pi_mutex);
- if (WARN_ON_ONCE(!top_waiter)) {
- /*
- * As per the comment in futex_unlock_pi() this should not happen.
- *
- * When this happens, give up our locks and try again, giving
- * the futex_lock_pi() instance time to complete, either by
- * waiting on the rtmutex or removing itself from the futex
- * queue.
- */
- ret = -EAGAIN;
- goto out_unlock;
- }
-
- new_owner = top_waiter->task;
-
- /*
- * We pass it to the next owner. The WAITERS bit is always kept
- * enabled while there is PI state around. We cleanup the owner
- * died bit, because we are the owner.
- */
- newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
-
- if (unlikely(should_fail_futex(true))) {
- ret = -EFAULT;
- goto out_unlock;
- }
-
- ret = futex_cmpxchg_value_locked(&curval, uaddr, uval, newval);
- if (!ret && (curval != uval)) {
- /*
- * If a unconditional UNLOCK_PI operation (user space did not
- * try the TID->0 transition) raced with a waiter setting the
- * FUTEX_WAITERS flag between get_user() and locking the hash
- * bucket lock, retry the operation.
- */
- if ((FUTEX_TID_MASK & curval) == uval)
- ret = -EAGAIN;
- else
- ret = -EINVAL;
- }
-
- if (!ret) {
- /*
- * This is a point of no return; once we modified the uval
- * there is no going back and subsequent operations must
- * not fail.
- */
- pi_state_update_owner(pi_state, new_owner);
- postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wqh);
- }
-
-out_unlock:
- raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
-
- if (postunlock)
- rt_mutex_postunlock(&wqh);
-
- return ret;
-}
-
-/*
* Express the locking dependencies for lockdep:
*/
static inline void
@@ -2410,7 +1575,7 @@ out_unlock:
}
/* The key must be already stored in q->key. */
-static inline struct futex_hash_bucket *futex_q_lock(struct futex_q *q)
+struct futex_hash_bucket *futex_q_lock(struct futex_q *q)
__acquires(&hb->lock)
{
struct futex_hash_bucket *hb;
@@ -2433,15 +1598,14 @@ static inline struct futex_hash_bucket *futex_q_lock(struct futex_q *q)
return hb;
}
-static inline void
-futex_q_unlock(struct futex_hash_bucket *hb)
+void futex_q_unlock(struct futex_hash_bucket *hb)
__releases(&hb->lock)
{
spin_unlock(&hb->lock);
hb_waiters_dec(hb);
}
-static inline void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb)
+void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb)
{
int prio;
@@ -2537,255 +1701,17 @@ retry:
* PI futexes can not be requeued and must remove themselves from the
* hash bucket. The hash bucket lock (i.e. lock_ptr) is held.
*/
-static void futex_unqueue_pi(struct futex_q *q)
+void futex_unqueue_pi(struct futex_q *q)
{
__futex_unqueue(q);
BUG_ON(!q->pi_state);
put_pi_state(q->pi_state);
- q->pi_state = NULL;
-}
-
-static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
- struct task_struct *argowner)
-{
- struct futex_pi_state *pi_state = q->pi_state;
- struct task_struct *oldowner, *newowner;
- u32 uval, curval, newval, newtid;
- int err = 0;
-
- oldowner = pi_state->owner;
-
- /*
- * We are here because either:
- *
- * - we stole the lock and pi_state->owner needs updating to reflect
- * that (@argowner == current),
- *
- * or:
- *
- * - someone stole our lock and we need to fix things to point to the
- * new owner (@argowner == NULL).
- *
- * Either way, we have to replace the TID in the user space variable.
- * This must be atomic as we have to preserve the owner died bit here.
- *
- * Note: We write the user space value _before_ changing the pi_state
- * because we can fault here. Imagine swapped out pages or a fork
- * that marked all the anonymous memory readonly for cow.
- *
- * Modifying pi_state _before_ the user space value would leave the
- * pi_state in an inconsistent state when we fault here, because we
- * need to drop the locks to handle the fault. This might be observed
- * in the PID checks when attaching to PI state .
- */
-retry:
- if (!argowner) {
- if (oldowner != current) {
- /*
- * We raced against a concurrent self; things are
- * already fixed up. Nothing to do.
- */
- return 0;
- }
-
- if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
- /* We got the lock. pi_state is correct. Tell caller. */
- return 1;
- }
-
- /*
- * The trylock just failed, so either there is an owner or
- * there is a higher priority waiter than this one.
- */
- newowner = rt_mutex_owner(&pi_state->pi_mutex);
- /*
- * If the higher priority waiter has not yet taken over the
- * rtmutex then newowner is NULL. We can't return here with
- * that state because it's inconsistent vs. the user space
- * state. So drop the locks and try again. It's a valid
- * situation and not any different from the other retry
- * conditions.
- */
- if (unlikely(!newowner)) {
- err = -EAGAIN;
- goto handle_err;
- }
- } else {
- WARN_ON_ONCE(argowner != current);
- if (oldowner == current) {
- /*
- * We raced against a concurrent self; things are
- * already fixed up. Nothing to do.
- */
- return 1;
- }
- newowner = argowner;
- }
-
- newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
- /* Owner died? */
- if (!pi_state->owner)
- newtid |= FUTEX_OWNER_DIED;
-
- err = futex_get_value_locked(&uval, uaddr);
- if (err)
- goto handle_err;
-
- for (;;) {
- newval = (uval & FUTEX_OWNER_DIED) | newtid;
-
- err = futex_cmpxchg_value_locked(&curval, uaddr, uval, newval);
- if (err)
- goto handle_err;
-
- if (curval == uval)
- break;
- uval = curval;
- }
-
- /*
- * We fixed up user space. Now we need to fix the pi_state
- * itself.
- */
- pi_state_update_owner(pi_state, newowner);
-
- return argowner == current;
-
- /*
- * In order to reschedule or handle a page fault, we need to drop the
- * locks here. In the case of a fault, this gives the other task
- * (either the highest priority waiter itself or the task which stole
- * the rtmutex) the chance to try the fixup of the pi_state. So once we
- * are back from handling the fault we need to check the pi_state after
- * reacquiring the locks and before trying to do another fixup. When
- * the fixup has been done already we simply return.
- *
- * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
- * drop hb->lock since the caller owns the hb -> futex_q relation.
- * Dropping the pi_mutex->wait_lock requires the state revalidate.
- */
-handle_err:
- raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
- spin_unlock(q->lock_ptr);
-
- switch (err) {
- case -EFAULT:
- err = fault_in_user_writeable(uaddr);
- break;
-
- case -EAGAIN:
- cond_resched();
- err = 0;
- break;
-
- default:
- WARN_ON_ONCE(1);
- break;
- }
-
- spin_lock(q->lock_ptr);
- raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
-
- /*
- * Check if someone else fixed it for us:
- */
- if (pi_state->owner != oldowner)
- return argowner == current;
-
- /* Retry if err was -EAGAIN or the fault in succeeded */
- if (!err)
- goto retry;
-
- /*
- * fault_in_user_writeable() failed so user state is immutable. At
- * best we can make the kernel state consistent but user state will
- * be most likely hosed and any subsequent unlock operation will be
- * rejected due to PI futex rule [10].
- *
- * Ensure that the rtmutex owner is also the pi_state owner despite
- * the user space value claiming something different. There is no
- * point in unlocking the rtmutex if current is the owner as it
- * would need to wait until the next waiter has taken the rtmutex
- * to guarantee consistent state. Keep it simple. Userspace asked
- * for this wreckaged state.
- *
- * The rtmutex has an owner - either current or some other
- * task. See the EAGAIN loop above.
- */
- pi_state_update_owner(pi_state, rt_mutex_owner(&pi_state->pi_mutex));
-
- return err;
-}
-
-static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
- struct task_struct *argowner)
-{
- struct futex_pi_state *pi_state = q->pi_state;
- int ret;
-
- lockdep_assert_held(q->lock_ptr);
-
- raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
- ret = __fixup_pi_state_owner(uaddr, q, argowner);
- raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
- return ret;
-}
-
-static long futex_wait_restart(struct restart_block *restart);
-
-/**
- * fixup_owner() - Post lock pi_state and corner case management
- * @uaddr: user address of the futex
- * @q: futex_q (contains pi_state and access to the rt_mutex)
- * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
- *
- * After attempting to lock an rt_mutex, this function is called to cleanup
- * the pi_state owner as well as handle race conditions that may allow us to
- * acquire the lock. Must be called with the hb lock held.
- *
- * Return:
- * - 1 - success, lock taken;
- * - 0 - success, lock not taken;
- * - <0 - on error (-EFAULT)
- */
-static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
-{
- if (locked) {
- /*
- * Got the lock. We might not be the anticipated owner if we
- * did a lock-steal - fix up the PI-state in that case:
- *
- * Speculative pi_state->owner read (we don't hold wait_lock);
- * since we own the lock pi_state->owner == current is the
- * stable state, anything else needs more attention.
- */
- if (q->pi_state->owner != current)
- return fixup_pi_state_owner(uaddr, q, current);
- return 1;
- }
-
- /*
- * If we didn't get the lock; check if anybody stole it from us. In
- * that case, we need to fix up the uval to point to them instead of
- * us, otherwise bad things happen. [10]
- *
- * Another speculative read; pi_state->owner == current is unstable
- * but needs our attention.
- */
- if (q->pi_state->owner == current)
- return fixup_pi_state_owner(uaddr, q, NULL);
-
- /*
- * Paranoia check. If we did not take the lock, then we should not be
- * the owner of the rt_mutex. Warn and establish consistent state.
- */
- if (WARN_ON_ONCE(rt_mutex_owner(&q->pi_state->pi_mutex) == current))
- return fixup_pi_state_owner(uaddr, q, current);
-
- return 0;
+ q->pi_state = NULL;
}
+static long futex_wait_restart(struct restart_block *restart);
+
/**
* futex_wait_queue() - futex_queue() and wait for wakeup, timeout, or signal
* @hb: the futex hash bucket, must be locked by the caller
@@ -2974,319 +1900,6 @@ static long futex_wait_restart(struct restart_block *restart)
}
-/*
- * Userspace tried a 0 -> TID atomic transition of the futex value
- * and failed. The kernel side here does the whole locking operation:
- * if there are waiters then it will block as a consequence of relying
- * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
- * a 0 value of the futex too.).
- *
- * Also serves as futex trylock_pi()'ing, and due semantics.
- */
-int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int trylock)
-{
- struct hrtimer_sleeper timeout, *to;
- struct task_struct *exiting = NULL;
- struct rt_mutex_waiter rt_waiter;
- struct futex_hash_bucket *hb;
- struct futex_q q = futex_q_init;
- int res, ret;
-
- if (!IS_ENABLED(CONFIG_FUTEX_PI))
- return -ENOSYS;
-
- if (refill_pi_state_cache())
- return -ENOMEM;
-
- to = futex_setup_timer(time, &timeout, flags, 0);
-
-retry:
- ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE);
- if (unlikely(ret != 0))
- goto out;
-
-retry_private:
- hb = futex_q_lock(&q);
-
- ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current,
- &exiting, 0);
- if (unlikely(ret)) {
- /*
- * Atomic work succeeded and we got the lock,
- * or failed. Either way, we do _not_ block.
- */
- switch (ret) {
- case 1:
- /* We got the lock. */
- ret = 0;
- goto out_unlock_put_key;
- case -EFAULT:
- goto uaddr_faulted;
- case -EBUSY:
- case -EAGAIN:
- /*
- * Two reasons for this:
- * - EBUSY: Task is exiting and we just wait for the
- * exit to complete.
- * - EAGAIN: The user space value changed.
- */
- futex_q_unlock(hb);
- /*
- * Handle the case where the owner is in the middle of
- * exiting. Wait for the exit to complete otherwise
- * this task might loop forever, aka. live lock.
- */
- wait_for_owner_exiting(ret, exiting);
- cond_resched();
- goto retry;
- default:
- goto out_unlock_put_key;
- }
- }
-
- WARN_ON(!q.pi_state);
-
- /*
- * Only actually queue now that the atomic ops are done:
- */
- __futex_queue(&q, hb);
-
- if (trylock) {
- ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
- /* Fixup the trylock return value: */
- ret = ret ? 0 : -EWOULDBLOCK;
- goto no_block;
- }
-
- rt_mutex_init_waiter(&rt_waiter);
-
- /*
- * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
- * hold it while doing rt_mutex_start_proxy(), because then it will
- * include hb->lock in the blocking chain, even through we'll not in
- * fact hold it while blocking. This will lead it to report -EDEADLK
- * and BUG when futex_unlock_pi() interleaves with this.
- *
- * Therefore acquire wait_lock while holding hb->lock, but drop the
- * latter before calling __rt_mutex_start_proxy_lock(). This
- * interleaves with futex_unlock_pi() -- which does a similar lock
- * handoff -- such that the latter can observe the futex_q::pi_state
- * before __rt_mutex_start_proxy_lock() is done.
- */
- raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
- spin_unlock(q.lock_ptr);
- /*
- * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
- * such that futex_unlock_pi() is guaranteed to observe the waiter when
- * it sees the futex_q::pi_state.
- */
- ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
- raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
-
- if (ret) {
- if (ret == 1)
- ret = 0;
- goto cleanup;
- }
-
- if (unlikely(to))
- hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS);
-
- ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
-
-cleanup:
- spin_lock(q.lock_ptr);
- /*
- * If we failed to acquire the lock (deadlock/signal/timeout), we must
- * first acquire the hb->lock before removing the lock from the
- * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
- * lists consistent.
- *
- * In particular; it is important that futex_unlock_pi() can not
- * observe this inconsistency.
- */
- if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
- ret = 0;
-
-no_block:
- /*
- * Fixup the pi_state owner and possibly acquire the lock if we
- * haven't already.
- */
- res = fixup_owner(uaddr, &q, !ret);
- /*
- * If fixup_owner() returned an error, propagate that. If it acquired
- * the lock, clear our -ETIMEDOUT or -EINTR.
- */
- if (res)
- ret = (res < 0) ? res : 0;
-
- futex_unqueue_pi(&q);
- spin_unlock(q.lock_ptr);
- goto out;
-
-out_unlock_put_key:
- futex_q_unlock(hb);
-
-out:
- if (to) {
- hrtimer_cancel(&to->timer);
- destroy_hrtimer_on_stack(&to->timer);
- }
- return ret != -EINTR ? ret : -ERESTARTNOINTR;
-
-uaddr_faulted:
- futex_q_unlock(hb);
-
- ret = fault_in_user_writeable(uaddr);
- if (ret)
- goto out;
-
- if (!(flags & FLAGS_SHARED))
- goto retry_private;
-
- goto retry;
-}
-
-/*
- * Userspace attempted a TID -> 0 atomic transition, and failed.
- * This is the in-kernel slowpath: we look up the PI state (if any),
- * and do the rt-mutex unlock.
- */
-int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
-{
- u32 curval, uval, vpid = task_pid_vnr(current);
- union futex_key key = FUTEX_KEY_INIT;
- struct futex_hash_bucket *hb;
- struct futex_q *top_waiter;
- int ret;
-
- if (!IS_ENABLED(CONFIG_FUTEX_PI))
- return -ENOSYS;
-
-retry:
- if (get_user(uval, uaddr))
- return -EFAULT;
- /*
- * We release only a lock we actually own:
- */
- if ((uval & FUTEX_TID_MASK) != vpid)
- return -EPERM;
-
- ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE);
- if (ret)
- return ret;
-
- hb = futex_hash(&key);
- spin_lock(&hb->lock);
-
- /*
- * Check waiters first. We do not trust user space values at
- * all and we at least want to know if user space fiddled
- * with the futex value instead of blindly unlocking.
- */
- top_waiter = futex_top_waiter(hb, &key);
- if (top_waiter) {
- struct futex_pi_state *pi_state = top_waiter->pi_state;
-
- ret = -EINVAL;
- if (!pi_state)
- goto out_unlock;
-
- /*
- * If current does not own the pi_state then the futex is
- * inconsistent and user space fiddled with the futex value.
- */
- if (pi_state->owner != current)
- goto out_unlock;
-
- get_pi_state(pi_state);
- /*
- * By taking wait_lock while still holding hb->lock, we ensure
- * there is no point where we hold neither; and therefore
- * wake_futex_pi() must observe a state consistent with what we
- * observed.
- *
- * In particular; this forces __rt_mutex_start_proxy() to
- * complete such that we're guaranteed to observe the
- * rt_waiter. Also see the WARN in wake_futex_pi().
- */
- raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
- spin_unlock(&hb->lock);
-
- /* drops pi_state->pi_mutex.wait_lock */
- ret = wake_futex_pi(uaddr, uval, pi_state);
-
- put_pi_state(pi_state);
-
- /*
- * Success, we're done! No tricky corner cases.
- */
- if (!ret)
- return ret;
- /*
- * The atomic access to the futex value generated a
- * pagefault, so retry the user-access and the wakeup:
- */
- if (ret == -EFAULT)
- goto pi_faulted;
- /*
- * A unconditional UNLOCK_PI op raced against a waiter
- * setting the FUTEX_WAITERS bit. Try again.
- */
- if (ret == -EAGAIN)
- goto pi_retry;
- /*
- * wake_futex_pi has detected invalid state. Tell user
- * space.
- */
- return ret;
- }
-
- /*
- * We have no kernel internal state, i.e. no waiters in the
- * kernel. Waiters which are about to queue themselves are stuck
- * on hb->lock. So we can safely ignore them. We do neither
- * preserve the WAITERS bit not the OWNER_DIED one. We are the
- * owner.
- */
- if ((ret = futex_cmpxchg_value_locked(&curval, uaddr, uval, 0))) {
- spin_unlock(&hb->lock);
- switch (ret) {
- case -EFAULT:
- goto pi_faulted;
-
- case -EAGAIN:
- goto pi_retry;
-
- default:
- WARN_ON_ONCE(1);
- return ret;
- }
- }
-
- /*
- * If uval has changed, let user space handle it.
- */
- ret = (curval == uval) ? 0 : -EAGAIN;
-
-out_unlock:
- spin_unlock(&hb->lock);
- return ret;
-
-pi_retry:
- cond_resched();
- goto retry;
-
-pi_faulted:
-
- ret = fault_in_user_writeable(uaddr);
- if (!ret)
- goto retry;
-
- return ret;
-}
-
/**
* handle_early_requeue_pi_wakeup() - Handle early wakeup on the initial futex
* @hb: the hash_bucket futex_q was original enqueued on
@@ -3441,7 +2054,7 @@ int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
/* The requeue acquired the lock */
if (q.pi_state && (q.pi_state->owner != current)) {
spin_lock(q.lock_ptr);
- ret = fixup_owner(uaddr2, &q, true);
+ ret = fixup_pi_owner(uaddr2, &q, true);
/*
* Drop the reference to the pi state which the
* requeue_pi() code acquired for us.
@@ -3471,9 +2084,9 @@ int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
* Fixup the pi_state owner and possibly acquire the lock if we
* haven't already.
*/
- res = fixup_owner(uaddr2, &q, !ret);
+ res = fixup_pi_owner(uaddr2, &q, !ret);
/*
- * If fixup_owner() returned an error, propagate that. If it
+ * If fixup_pi_owner() returned an error, propagate that. If it
* acquired the lock, clear -ETIMEDOUT or -EINTR.
*/
if (res)
@@ -3811,6 +2424,87 @@ static void compat_exit_robust_list(struct task_struct *curr)
}
#endif
+#ifdef CONFIG_FUTEX_PI
+
+/*
+ * This task is holding PI mutexes at exit time => bad.
+ * Kernel cleans up PI-state, but userspace is likely hosed.
+ * (Robust-futex cleanup is separate and might save the day for userspace.)
+ */
+static void exit_pi_state_list(struct task_struct *curr)
+{
+ struct list_head *next, *head = &curr->pi_state_list;
+ struct futex_pi_state *pi_state;
+ struct futex_hash_bucket *hb;
+ union futex_key key = FUTEX_KEY_INIT;
+
+ if (!futex_cmpxchg_enabled)
+ return;
+ /*
+ * We are a ZOMBIE and nobody can enqueue itself on
+ * pi_state_list anymore, but we have to be careful
+ * versus waiters unqueueing themselves:
+ */
+ raw_spin_lock_irq(&curr->pi_lock);
+ while (!list_empty(head)) {
+ next = head->next;
+ pi_state = list_entry(next, struct futex_pi_state, list);
+ key = pi_state->key;
+ hb = futex_hash(&key);
+
+ /*
+ * We can race against put_pi_state() removing itself from the
+ * list (a waiter going away). put_pi_state() will first
+ * decrement the reference count and then modify the list, so
+ * its possible to see the list entry but fail this reference
+ * acquire.
+ *
+ * In that case; drop the locks to let put_pi_state() make
+ * progress and retry the loop.
+ */
+ if (!refcount_inc_not_zero(&pi_state->refcount)) {
+ raw_spin_unlock_irq(&curr->pi_lock);
+ cpu_relax();
+ raw_spin_lock_irq(&curr->pi_lock);
+ continue;
+ }
+ raw_spin_unlock_irq(&curr->pi_lock);
+
+ spin_lock(&hb->lock);
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+ raw_spin_lock(&curr->pi_lock);
+ /*
+ * We dropped the pi-lock, so re-check whether this
+ * task still owns the PI-state:
+ */
+ if (head->next != next) {
+ /* retain curr->pi_lock for the loop invariant */
+ raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
+ spin_unlock(&hb->lock);
+ put_pi_state(pi_state);
+ continue;
+ }
+
+ WARN_ON(pi_state->owner != curr);
+ WARN_ON(list_empty(&pi_state->list));
+ list_del_init(&pi_state->list);
+ pi_state->owner = NULL;
+
+ raw_spin_unlock(&curr->pi_lock);
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+ spin_unlock(&hb->lock);
+
+ rt_mutex_futex_unlock(&pi_state->pi_mutex);
+ put_pi_state(pi_state);
+
+ raw_spin_lock_irq(&curr->pi_lock);
+ }
+ raw_spin_unlock_irq(&curr->pi_lock);
+}
+#else
+static inline void exit_pi_state_list(struct task_struct *curr) { }
+#endif
+
static void futex_cleanup(struct task_struct *tsk)
{
if (unlikely(tsk->robust_list)) {
diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
index 7bb4ca8..4969e96 100644
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -2,6 +2,7 @@
#ifndef _FUTEX_H
#define _FUTEX_H
+#include <linux/futex.h>
#include <asm/futex.h>
/*
@@ -35,6 +36,122 @@ static inline bool should_fail_futex(bool fshared)
}
#endif
+/*
+ * Hash buckets are shared by all the futex_keys that hash to the same
+ * location. Each key may have multiple futex_q structures, one for each task
+ * waiting on a futex.
+ */
+struct futex_hash_bucket {
+ atomic_t waiters;
+ spinlock_t lock;
+ struct plist_head chain;
+} ____cacheline_aligned_in_smp;
+
+/*
+ * Priority Inheritance state:
+ */
+struct futex_pi_state {
+ /*
+ * list of 'owned' pi_state instances - these have to be
+ * cleaned up in do_exit() if the task exits prematurely:
+ */
+ struct list_head list;
+
+ /*
+ * The PI object:
+ */
+ struct rt_mutex_base pi_mutex;
+
+ struct task_struct *owner;
+ refcount_t refcount;
+
+ union futex_key key;
+} __randomize_layout;
+
+/**
+ * struct futex_q - The hashed futex queue entry, one per waiting task
+ * @list: priority-sorted list of tasks waiting on this futex
+ * @task: the task waiting on the futex
+ * @lock_ptr: the hash bucket lock
+ * @key: the key the futex is hashed on
+ * @pi_state: optional priority inheritance state
+ * @rt_waiter: rt_waiter storage for use with requeue_pi
+ * @requeue_pi_key: the requeue_pi target futex key
+ * @bitset: bitset for the optional bitmasked wakeup
+ * @requeue_state: State field for futex_requeue_pi()
+ * @requeue_wait: RCU wait for futex_requeue_pi() (RT only)
+ *
+ * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so
+ * we can wake only the relevant ones (hashed queues may be shared).
+ *
+ * A futex_q has a woken state, just like tasks have TASK_RUNNING.
+ * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
+ * The order of wakeup is always to make the first condition true, then
+ * the second.
+ *
+ * PI futexes are typically woken before they are removed from the hash list via
+ * the rt_mutex code. See futex_unqueue_pi().
+ */
+struct futex_q {
+ struct plist_node list;
+
+ struct task_struct *task;
+ spinlock_t *lock_ptr;
+ union futex_key key;
+ struct futex_pi_state *pi_state;
+ struct rt_mutex_waiter *rt_waiter;
+ union futex_key *requeue_pi_key;
+ u32 bitset;
+ atomic_t requeue_state;
+#ifdef CONFIG_PREEMPT_RT
+ struct rcuwait requeue_wait;
+#endif
+} __randomize_layout;
+
+extern const struct futex_q futex_q_init;
+
+enum futex_access {
+ FUTEX_READ,
+ FUTEX_WRITE
+};
+
+extern int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key,
+ enum futex_access rw);
+
+extern struct futex_hash_bucket *futex_hash(union futex_key *key);
+
+extern struct hrtimer_sleeper *
+futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout,
+ int flags, u64 range_ns);
+
+extern int fault_in_user_writeable(u32 __user *uaddr);
+extern int futex_cmpxchg_value_locked(u32 *curval, u32 __user *uaddr, u32 uval, u32 newval);
+extern int futex_get_value_locked(u32 *dest, u32 __user *from);
+extern struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb, union futex_key *key);
+
+extern void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb);
+extern void futex_unqueue_pi(struct futex_q *q);
+
+extern void wait_for_owner_exiting(int ret, struct task_struct *exiting);
+
+extern struct futex_hash_bucket *futex_q_lock(struct futex_q *q);
+extern void futex_q_unlock(struct futex_hash_bucket *hb);
+
+
+extern int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
+ union futex_key *key,
+ struct futex_pi_state **ps,
+ struct task_struct *task,
+ struct task_struct **exiting,
+ int set_waiters);
+
+extern int refill_pi_state_cache(void);
+extern void get_pi_state(struct futex_pi_state *pi_state);
+extern void put_pi_state(struct futex_pi_state *pi_state);
+extern int fixup_pi_owner(u32 __user *uaddr, struct futex_q *q, int locked);
+
+/* syscalls */
+
extern int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, u32
val, ktime_t *abs_time, u32 bitset, u32 __user
*uaddr2);
diff --git a/kernel/futex/pi.c b/kernel/futex/pi.c
new file mode 100644
index 0000000..183b28c
--- /dev/null
+++ b/kernel/futex/pi.c
@@ -0,0 +1,1233 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/slab.h>
+#include <linux/sched/task.h>
+
+#include "futex.h"
+#include "../locking/rtmutex_common.h"
+
+/*
+ * PI code:
+ */
+int refill_pi_state_cache(void)
+{
+ struct futex_pi_state *pi_state;
+
+ if (likely(current->pi_state_cache))
+ return 0;
+
+ pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
+
+ if (!pi_state)
+ return -ENOMEM;
+
+ INIT_LIST_HEAD(&pi_state->list);
+ /* pi_mutex gets initialized later */
+ pi_state->owner = NULL;
+ refcount_set(&pi_state->refcount, 1);
+ pi_state->key = FUTEX_KEY_INIT;
+
+ current->pi_state_cache = pi_state;
+
+ return 0;
+}
+
+static struct futex_pi_state *alloc_pi_state(void)
+{
+ struct futex_pi_state *pi_state = current->pi_state_cache;
+
+ WARN_ON(!pi_state);
+ current->pi_state_cache = NULL;
+
+ return pi_state;
+}
+
+static void pi_state_update_owner(struct futex_pi_state *pi_state,
+ struct task_struct *new_owner)
+{
+ struct task_struct *old_owner = pi_state->owner;
+
+ lockdep_assert_held(&pi_state->pi_mutex.wait_lock);
+
+ if (old_owner) {
+ raw_spin_lock(&old_owner->pi_lock);
+ WARN_ON(list_empty(&pi_state->list));
+ list_del_init(&pi_state->list);
+ raw_spin_unlock(&old_owner->pi_lock);
+ }
+
+ if (new_owner) {
+ raw_spin_lock(&new_owner->pi_lock);
+ WARN_ON(!list_empty(&pi_state->list));
+ list_add(&pi_state->list, &new_owner->pi_state_list);
+ pi_state->owner = new_owner;
+ raw_spin_unlock(&new_owner->pi_lock);
+ }
+}
+
+void get_pi_state(struct futex_pi_state *pi_state)
+{
+ WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
+}
+
+/*
+ * Drops a reference to the pi_state object and frees or caches it
+ * when the last reference is gone.
+ */
+void put_pi_state(struct futex_pi_state *pi_state)
+{
+ if (!pi_state)
+ return;
+
+ if (!refcount_dec_and_test(&pi_state->refcount))
+ return;
+
+ /*
+ * If pi_state->owner is NULL, the owner is most probably dying
+ * and has cleaned up the pi_state already
+ */
+ if (pi_state->owner) {
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
+ pi_state_update_owner(pi_state, NULL);
+ rt_mutex_proxy_unlock(&pi_state->pi_mutex);
+ raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
+ }
+
+ if (current->pi_state_cache) {
+ kfree(pi_state);
+ } else {
+ /*
+ * pi_state->list is already empty.
+ * clear pi_state->owner.
+ * refcount is at 0 - put it back to 1.
+ */
+ pi_state->owner = NULL;
+ refcount_set(&pi_state->refcount, 1);
+ current->pi_state_cache = pi_state;
+ }
+}
+
+/*
+ * We need to check the following states:
+ *
+ * Waiter | pi_state | pi->owner | uTID | uODIED | ?
+ *
+ * [1] NULL | --- | --- | 0 | 0/1 | Valid
+ * [2] NULL | --- | --- | >0 | 0/1 | Valid
+ *
+ * [3] Found | NULL | -- | Any | 0/1 | Invalid
+ *
+ * [4] Found | Found | NULL | 0 | 1 | Valid
+ * [5] Found | Found | NULL | >0 | 1 | Invalid
+ *
+ * [6] Found | Found | task | 0 | 1 | Valid
+ *
+ * [7] Found | Found | NULL | Any | 0 | Invalid
+ *
+ * [8] Found | Found | task | ==taskTID | 0/1 | Valid
+ * [9] Found | Found | task | 0 | 0 | Invalid
+ * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
+ *
+ * [1] Indicates that the kernel can acquire the futex atomically. We
+ * came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
+ *
+ * [2] Valid, if TID does not belong to a kernel thread. If no matching
+ * thread is found then it indicates that the owner TID has died.
+ *
+ * [3] Invalid. The waiter is queued on a non PI futex
+ *
+ * [4] Valid state after exit_robust_list(), which sets the user space
+ * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
+ *
+ * [5] The user space value got manipulated between exit_robust_list()
+ * and exit_pi_state_list()
+ *
+ * [6] Valid state after exit_pi_state_list() which sets the new owner in
+ * the pi_state but cannot access the user space value.
+ *
+ * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
+ *
+ * [8] Owner and user space value match
+ *
+ * [9] There is no transient state which sets the user space TID to 0
+ * except exit_robust_list(), but this is indicated by the
+ * FUTEX_OWNER_DIED bit. See [4]
+ *
+ * [10] There is no transient state which leaves owner and user space
+ * TID out of sync. Except one error case where the kernel is denied
+ * write access to the user address, see fixup_pi_state_owner().
+ *
+ *
+ * Serialization and lifetime rules:
+ *
+ * hb->lock:
+ *
+ * hb -> futex_q, relation
+ * futex_q -> pi_state, relation
+ *
+ * (cannot be raw because hb can contain arbitrary amount
+ * of futex_q's)
+ *
+ * pi_mutex->wait_lock:
+ *
+ * {uval, pi_state}
+ *
+ * (and pi_mutex 'obviously')
+ *
+ * p->pi_lock:
+ *
+ * p->pi_state_list -> pi_state->list, relation
+ * pi_mutex->owner -> pi_state->owner, relation
+ *
+ * pi_state->refcount:
+ *
+ * pi_state lifetime
+ *
+ *
+ * Lock order:
+ *
+ * hb->lock
+ * pi_mutex->wait_lock
+ * p->pi_lock
+ *
+ */
+
+/*
+ * Validate that the existing waiter has a pi_state and sanity check
+ * the pi_state against the user space value. If correct, attach to
+ * it.
+ */
+static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
+ struct futex_pi_state *pi_state,
+ struct futex_pi_state **ps)
+{
+ pid_t pid = uval & FUTEX_TID_MASK;
+ u32 uval2;
+ int ret;
+
+ /*
+ * Userspace might have messed up non-PI and PI futexes [3]
+ */
+ if (unlikely(!pi_state))
+ return -EINVAL;
+
+ /*
+ * We get here with hb->lock held, and having found a
+ * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
+ * has dropped the hb->lock in between futex_queue() and futex_unqueue_pi(),
+ * which in turn means that futex_lock_pi() still has a reference on
+ * our pi_state.
+ *
+ * The waiter holding a reference on @pi_state also protects against
+ * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
+ * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
+ * free pi_state before we can take a reference ourselves.
+ */
+ WARN_ON(!refcount_read(&pi_state->refcount));
+
+ /*
+ * Now that we have a pi_state, we can acquire wait_lock
+ * and do the state validation.
+ */
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+
+ /*
+ * Since {uval, pi_state} is serialized by wait_lock, and our current
+ * uval was read without holding it, it can have changed. Verify it
+ * still is what we expect it to be, otherwise retry the entire
+ * operation.
+ */
+ if (futex_get_value_locked(&uval2, uaddr))
+ goto out_efault;
+
+ if (uval != uval2)
+ goto out_eagain;
+
+ /*
+ * Handle the owner died case:
+ */
+ if (uval & FUTEX_OWNER_DIED) {
+ /*
+ * exit_pi_state_list sets owner to NULL and wakes the
+ * topmost waiter. The task which acquires the
+ * pi_state->rt_mutex will fixup owner.
+ */
+ if (!pi_state->owner) {
+ /*
+ * No pi state owner, but the user space TID
+ * is not 0. Inconsistent state. [5]
+ */
+ if (pid)
+ goto out_einval;
+ /*
+ * Take a ref on the state and return success. [4]
+ */
+ goto out_attach;
+ }
+
+ /*
+ * If TID is 0, then either the dying owner has not
+ * yet executed exit_pi_state_list() or some waiter
+ * acquired the rtmutex in the pi state, but did not
+ * yet fixup the TID in user space.
+ *
+ * Take a ref on the state and return success. [6]
+ */
+ if (!pid)
+ goto out_attach;
+ } else {
+ /*
+ * If the owner died bit is not set, then the pi_state
+ * must have an owner. [7]
+ */
+ if (!pi_state->owner)
+ goto out_einval;
+ }
+
+ /*
+ * Bail out if user space manipulated the futex value. If pi
+ * state exists then the owner TID must be the same as the
+ * user space TID. [9/10]
+ */
+ if (pid != task_pid_vnr(pi_state->owner))
+ goto out_einval;
+
+out_attach:
+ get_pi_state(pi_state);
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+ *ps = pi_state;
+ return 0;
+
+out_einval:
+ ret = -EINVAL;
+ goto out_error;
+
+out_eagain:
+ ret = -EAGAIN;
+ goto out_error;
+
+out_efault:
+ ret = -EFAULT;
+ goto out_error;
+
+out_error:
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+ return ret;
+}
+
+static int handle_exit_race(u32 __user *uaddr, u32 uval,
+ struct task_struct *tsk)
+{
+ u32 uval2;
+
+ /*
+ * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
+ * caller that the alleged owner is busy.
+ */
+ if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
+ return -EBUSY;
+
+ /*
+ * Reread the user space value to handle the following situation:
+ *
+ * CPU0 CPU1
+ *
+ * sys_exit() sys_futex()
+ * do_exit() futex_lock_pi()
+ * futex_lock_pi_atomic()
+ * exit_signals(tsk) No waiters:
+ * tsk->flags |= PF_EXITING; *uaddr == 0x00000PID
+ * mm_release(tsk) Set waiter bit
+ * exit_robust_list(tsk) { *uaddr = 0x80000PID;
+ * Set owner died attach_to_pi_owner() {
+ * *uaddr = 0xC0000000; tsk = get_task(PID);
+ * } if (!tsk->flags & PF_EXITING) {
+ * ... attach();
+ * tsk->futex_state = } else {
+ * FUTEX_STATE_DEAD; if (tsk->futex_state !=
+ * FUTEX_STATE_DEAD)
+ * return -EAGAIN;
+ * return -ESRCH; <--- FAIL
+ * }
+ *
+ * Returning ESRCH unconditionally is wrong here because the
+ * user space value has been changed by the exiting task.
+ *
+ * The same logic applies to the case where the exiting task is
+ * already gone.
+ */
+ if (futex_get_value_locked(&uval2, uaddr))
+ return -EFAULT;
+
+ /* If the user space value has changed, try again. */
+ if (uval2 != uval)
+ return -EAGAIN;
+
+ /*
+ * The exiting task did not have a robust list, the robust list was
+ * corrupted or the user space value in *uaddr is simply bogus.
+ * Give up and tell user space.
+ */
+ return -ESRCH;
+}
+
+static void __attach_to_pi_owner(struct task_struct *p, union futex_key *key,
+ struct futex_pi_state **ps)
+{
+ /*
+ * No existing pi state. First waiter. [2]
+ *
+ * This creates pi_state, we have hb->lock held, this means nothing can
+ * observe this state, wait_lock is irrelevant.
+ */
+ struct futex_pi_state *pi_state = alloc_pi_state();
+
+ /*
+ * Initialize the pi_mutex in locked state and make @p
+ * the owner of it:
+ */
+ rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
+
+ /* Store the key for possible exit cleanups: */
+ pi_state->key = *key;
+
+ WARN_ON(!list_empty(&pi_state->list));
+ list_add(&pi_state->list, &p->pi_state_list);
+ /*
+ * Assignment without holding pi_state->pi_mutex.wait_lock is safe
+ * because there is no concurrency as the object is not published yet.
+ */
+ pi_state->owner = p;
+
+ *ps = pi_state;
+}
+/*
+ * Lookup the task for the TID provided from user space and attach to
+ * it after doing proper sanity checks.
+ */
+static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key,
+ struct futex_pi_state **ps,
+ struct task_struct **exiting)
+{
+ pid_t pid = uval & FUTEX_TID_MASK;
+ struct task_struct *p;
+
+ /*
+ * We are the first waiter - try to look up the real owner and attach
+ * the new pi_state to it, but bail out when TID = 0 [1]
+ *
+ * The !pid check is paranoid. None of the call sites should end up
+ * with pid == 0, but better safe than sorry. Let the caller retry
+ */
+ if (!pid)
+ return -EAGAIN;
+ p = find_get_task_by_vpid(pid);
+ if (!p)
+ return handle_exit_race(uaddr, uval, NULL);
+
+ if (unlikely(p->flags & PF_KTHREAD)) {
+ put_task_struct(p);
+ return -EPERM;
+ }
+
+ /*
+ * We need to look at the task state to figure out, whether the
+ * task is exiting. To protect against the change of the task state
+ * in futex_exit_release(), we do this protected by p->pi_lock:
+ */
+ raw_spin_lock_irq(&p->pi_lock);
+ if (unlikely(p->futex_state != FUTEX_STATE_OK)) {
+ /*
+ * The task is on the way out. When the futex state is
+ * FUTEX_STATE_DEAD, we know that the task has finished
+ * the cleanup:
+ */
+ int ret = handle_exit_race(uaddr, uval, p);
+
+ raw_spin_unlock_irq(&p->pi_lock);
+ /*
+ * If the owner task is between FUTEX_STATE_EXITING and
+ * FUTEX_STATE_DEAD then store the task pointer and keep
+ * the reference on the task struct. The calling code will
+ * drop all locks, wait for the task to reach
+ * FUTEX_STATE_DEAD and then drop the refcount. This is
+ * required to prevent a live lock when the current task
+ * preempted the exiting task between the two states.
+ */
+ if (ret == -EBUSY)
+ *exiting = p;
+ else
+ put_task_struct(p);
+ return ret;
+ }
+
+ __attach_to_pi_owner(p, key, ps);
+ raw_spin_unlock_irq(&p->pi_lock);
+
+ put_task_struct(p);
+
+ return 0;
+}
+
+static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
+{
+ int err;
+ u32 curval;
+
+ if (unlikely(should_fail_futex(true)))
+ return -EFAULT;
+
+ err = futex_cmpxchg_value_locked(&curval, uaddr, uval, newval);
+ if (unlikely(err))
+ return err;
+
+ /* If user space value changed, let the caller retry */
+ return curval != uval ? -EAGAIN : 0;
+}
+
+/**
+ * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
+ * @uaddr: the pi futex user address
+ * @hb: the pi futex hash bucket
+ * @key: the futex key associated with uaddr and hb
+ * @ps: the pi_state pointer where we store the result of the
+ * lookup
+ * @task: the task to perform the atomic lock work for. This will
+ * be "current" except in the case of requeue pi.
+ * @exiting: Pointer to store the task pointer of the owner task
+ * which is in the middle of exiting
+ * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
+ *
+ * Return:
+ * - 0 - ready to wait;
+ * - 1 - acquired the lock;
+ * - <0 - error
+ *
+ * The hb->lock must be held by the caller.
+ *
+ * @exiting is only set when the return value is -EBUSY. If so, this holds
+ * a refcount on the exiting task on return and the caller needs to drop it
+ * after waiting for the exit to complete.
+ */
+int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
+ union futex_key *key,
+ struct futex_pi_state **ps,
+ struct task_struct *task,
+ struct task_struct **exiting,
+ int set_waiters)
+{
+ u32 uval, newval, vpid = task_pid_vnr(task);
+ struct futex_q *top_waiter;
+ int ret;
+
+ /*
+ * Read the user space value first so we can validate a few
+ * things before proceeding further.
+ */
+ if (futex_get_value_locked(&uval, uaddr))
+ return -EFAULT;
+
+ if (unlikely(should_fail_futex(true)))
+ return -EFAULT;
+
+ /*
+ * Detect deadlocks.
+ */
+ if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
+ return -EDEADLK;
+
+ if ((unlikely(should_fail_futex(true))))
+ return -EDEADLK;
+
+ /*
+ * Lookup existing state first. If it exists, try to attach to
+ * its pi_state.
+ */
+ top_waiter = futex_top_waiter(hb, key);
+ if (top_waiter)
+ return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
+
+ /*
+ * No waiter and user TID is 0. We are here because the
+ * waiters or the owner died bit is set or called from
+ * requeue_cmp_pi or for whatever reason something took the
+ * syscall.
+ */
+ if (!(uval & FUTEX_TID_MASK)) {
+ /*
+ * We take over the futex. No other waiters and the user space
+ * TID is 0. We preserve the owner died bit.
+ */
+ newval = uval & FUTEX_OWNER_DIED;
+ newval |= vpid;
+
+ /* The futex requeue_pi code can enforce the waiters bit */
+ if (set_waiters)
+ newval |= FUTEX_WAITERS;
+
+ ret = lock_pi_update_atomic(uaddr, uval, newval);
+ if (ret)
+ return ret;
+
+ /*
+ * If the waiter bit was requested the caller also needs PI
+ * state attached to the new owner of the user space futex.
+ *
+ * @task is guaranteed to be alive and it cannot be exiting
+ * because it is either sleeping or waiting in
+ * futex_requeue_pi_wakeup_sync().
+ *
+ * No need to do the full attach_to_pi_owner() exercise
+ * because @task is known and valid.
+ */
+ if (set_waiters) {
+ raw_spin_lock_irq(&task->pi_lock);
+ __attach_to_pi_owner(task, key, ps);
+ raw_spin_unlock_irq(&task->pi_lock);
+ }
+ return 1;
+ }
+
+ /*
+ * First waiter. Set the waiters bit before attaching ourself to
+ * the owner. If owner tries to unlock, it will be forced into
+ * the kernel and blocked on hb->lock.
+ */
+ newval = uval | FUTEX_WAITERS;
+ ret = lock_pi_update_atomic(uaddr, uval, newval);
+ if (ret)
+ return ret;
+ /*
+ * If the update of the user space value succeeded, we try to
+ * attach to the owner. If that fails, no harm done, we only
+ * set the FUTEX_WAITERS bit in the user space variable.
+ */
+ return attach_to_pi_owner(uaddr, newval, key, ps, exiting);
+}
+
+/*
+ * Caller must hold a reference on @pi_state.
+ */
+static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
+{
+ struct rt_mutex_waiter *top_waiter;
+ struct task_struct *new_owner;
+ bool postunlock = false;
+ DEFINE_RT_WAKE_Q(wqh);
+ u32 curval, newval;
+ int ret = 0;
+
+ top_waiter = rt_mutex_top_waiter(&pi_state->pi_mutex);
+ if (WARN_ON_ONCE(!top_waiter)) {
+ /*
+ * As per the comment in futex_unlock_pi() this should not happen.
+ *
+ * When this happens, give up our locks and try again, giving
+ * the futex_lock_pi() instance time to complete, either by
+ * waiting on the rtmutex or removing itself from the futex
+ * queue.
+ */
+ ret = -EAGAIN;
+ goto out_unlock;
+ }
+
+ new_owner = top_waiter->task;
+
+ /*
+ * We pass it to the next owner. The WAITERS bit is always kept
+ * enabled while there is PI state around. We cleanup the owner
+ * died bit, because we are the owner.
+ */
+ newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
+
+ if (unlikely(should_fail_futex(true))) {
+ ret = -EFAULT;
+ goto out_unlock;
+ }
+
+ ret = futex_cmpxchg_value_locked(&curval, uaddr, uval, newval);
+ if (!ret && (curval != uval)) {
+ /*
+ * If a unconditional UNLOCK_PI operation (user space did not
+ * try the TID->0 transition) raced with a waiter setting the
+ * FUTEX_WAITERS flag between get_user() and locking the hash
+ * bucket lock, retry the operation.
+ */
+ if ((FUTEX_TID_MASK & curval) == uval)
+ ret = -EAGAIN;
+ else
+ ret = -EINVAL;
+ }
+
+ if (!ret) {
+ /*
+ * This is a point of no return; once we modified the uval
+ * there is no going back and subsequent operations must
+ * not fail.
+ */
+ pi_state_update_owner(pi_state, new_owner);
+ postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wqh);
+ }
+
+out_unlock:
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+
+ if (postunlock)
+ rt_mutex_postunlock(&wqh);
+
+ return ret;
+}
+
+static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
+ struct task_struct *argowner)
+{
+ struct futex_pi_state *pi_state = q->pi_state;
+ struct task_struct *oldowner, *newowner;
+ u32 uval, curval, newval, newtid;
+ int err = 0;
+
+ oldowner = pi_state->owner;
+
+ /*
+ * We are here because either:
+ *
+ * - we stole the lock and pi_state->owner needs updating to reflect
+ * that (@argowner == current),
+ *
+ * or:
+ *
+ * - someone stole our lock and we need to fix things to point to the
+ * new owner (@argowner == NULL).
+ *
+ * Either way, we have to replace the TID in the user space variable.
+ * This must be atomic as we have to preserve the owner died bit here.
+ *
+ * Note: We write the user space value _before_ changing the pi_state
+ * because we can fault here. Imagine swapped out pages or a fork
+ * that marked all the anonymous memory readonly for cow.
+ *
+ * Modifying pi_state _before_ the user space value would leave the
+ * pi_state in an inconsistent state when we fault here, because we
+ * need to drop the locks to handle the fault. This might be observed
+ * in the PID checks when attaching to PI state .
+ */
+retry:
+ if (!argowner) {
+ if (oldowner != current) {
+ /*
+ * We raced against a concurrent self; things are
+ * already fixed up. Nothing to do.
+ */
+ return 0;
+ }
+
+ if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
+ /* We got the lock. pi_state is correct. Tell caller. */
+ return 1;
+ }
+
+ /*
+ * The trylock just failed, so either there is an owner or
+ * there is a higher priority waiter than this one.
+ */
+ newowner = rt_mutex_owner(&pi_state->pi_mutex);
+ /*
+ * If the higher priority waiter has not yet taken over the
+ * rtmutex then newowner is NULL. We can't return here with
+ * that state because it's inconsistent vs. the user space
+ * state. So drop the locks and try again. It's a valid
+ * situation and not any different from the other retry
+ * conditions.
+ */
+ if (unlikely(!newowner)) {
+ err = -EAGAIN;
+ goto handle_err;
+ }
+ } else {
+ WARN_ON_ONCE(argowner != current);
+ if (oldowner == current) {
+ /*
+ * We raced against a concurrent self; things are
+ * already fixed up. Nothing to do.
+ */
+ return 1;
+ }
+ newowner = argowner;
+ }
+
+ newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
+ /* Owner died? */
+ if (!pi_state->owner)
+ newtid |= FUTEX_OWNER_DIED;
+
+ err = futex_get_value_locked(&uval, uaddr);
+ if (err)
+ goto handle_err;
+
+ for (;;) {
+ newval = (uval & FUTEX_OWNER_DIED) | newtid;
+
+ err = futex_cmpxchg_value_locked(&curval, uaddr, uval, newval);
+ if (err)
+ goto handle_err;
+
+ if (curval == uval)
+ break;
+ uval = curval;
+ }
+
+ /*
+ * We fixed up user space. Now we need to fix the pi_state
+ * itself.
+ */
+ pi_state_update_owner(pi_state, newowner);
+
+ return argowner == current;
+
+ /*
+ * In order to reschedule or handle a page fault, we need to drop the
+ * locks here. In the case of a fault, this gives the other task
+ * (either the highest priority waiter itself or the task which stole
+ * the rtmutex) the chance to try the fixup of the pi_state. So once we
+ * are back from handling the fault we need to check the pi_state after
+ * reacquiring the locks and before trying to do another fixup. When
+ * the fixup has been done already we simply return.
+ *
+ * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
+ * drop hb->lock since the caller owns the hb -> futex_q relation.
+ * Dropping the pi_mutex->wait_lock requires the state revalidate.
+ */
+handle_err:
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+ spin_unlock(q->lock_ptr);
+
+ switch (err) {
+ case -EFAULT:
+ err = fault_in_user_writeable(uaddr);
+ break;
+
+ case -EAGAIN:
+ cond_resched();
+ err = 0;
+ break;
+
+ default:
+ WARN_ON_ONCE(1);
+ break;
+ }
+
+ spin_lock(q->lock_ptr);
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+
+ /*
+ * Check if someone else fixed it for us:
+ */
+ if (pi_state->owner != oldowner)
+ return argowner == current;
+
+ /* Retry if err was -EAGAIN or the fault in succeeded */
+ if (!err)
+ goto retry;
+
+ /*
+ * fault_in_user_writeable() failed so user state is immutable. At
+ * best we can make the kernel state consistent but user state will
+ * be most likely hosed and any subsequent unlock operation will be
+ * rejected due to PI futex rule [10].
+ *
+ * Ensure that the rtmutex owner is also the pi_state owner despite
+ * the user space value claiming something different. There is no
+ * point in unlocking the rtmutex if current is the owner as it
+ * would need to wait until the next waiter has taken the rtmutex
+ * to guarantee consistent state. Keep it simple. Userspace asked
+ * for this wreckaged state.
+ *
+ * The rtmutex has an owner - either current or some other
+ * task. See the EAGAIN loop above.
+ */
+ pi_state_update_owner(pi_state, rt_mutex_owner(&pi_state->pi_mutex));
+
+ return err;
+}
+
+static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
+ struct task_struct *argowner)
+{
+ struct futex_pi_state *pi_state = q->pi_state;
+ int ret;
+
+ lockdep_assert_held(q->lock_ptr);
+
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+ ret = __fixup_pi_state_owner(uaddr, q, argowner);
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+ return ret;
+}
+
+/**
+ * fixup_pi_owner() - Post lock pi_state and corner case management
+ * @uaddr: user address of the futex
+ * @q: futex_q (contains pi_state and access to the rt_mutex)
+ * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
+ *
+ * After attempting to lock an rt_mutex, this function is called to cleanup
+ * the pi_state owner as well as handle race conditions that may allow us to
+ * acquire the lock. Must be called with the hb lock held.
+ *
+ * Return:
+ * - 1 - success, lock taken;
+ * - 0 - success, lock not taken;
+ * - <0 - on error (-EFAULT)
+ */
+int fixup_pi_owner(u32 __user *uaddr, struct futex_q *q, int locked)
+{
+ if (locked) {
+ /*
+ * Got the lock. We might not be the anticipated owner if we
+ * did a lock-steal - fix up the PI-state in that case:
+ *
+ * Speculative pi_state->owner read (we don't hold wait_lock);
+ * since we own the lock pi_state->owner == current is the
+ * stable state, anything else needs more attention.
+ */
+ if (q->pi_state->owner != current)
+ return fixup_pi_state_owner(uaddr, q, current);
+ return 1;
+ }
+
+ /*
+ * If we didn't get the lock; check if anybody stole it from us. In
+ * that case, we need to fix up the uval to point to them instead of
+ * us, otherwise bad things happen. [10]
+ *
+ * Another speculative read; pi_state->owner == current is unstable
+ * but needs our attention.
+ */
+ if (q->pi_state->owner == current)
+ return fixup_pi_state_owner(uaddr, q, NULL);
+
+ /*
+ * Paranoia check. If we did not take the lock, then we should not be
+ * the owner of the rt_mutex. Warn and establish consistent state.
+ */
+ if (WARN_ON_ONCE(rt_mutex_owner(&q->pi_state->pi_mutex) == current))
+ return fixup_pi_state_owner(uaddr, q, current);
+
+ return 0;
+}
+
+/*
+ * Userspace tried a 0 -> TID atomic transition of the futex value
+ * and failed. The kernel side here does the whole locking operation:
+ * if there are waiters then it will block as a consequence of relying
+ * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
+ * a 0 value of the futex too.).
+ *
+ * Also serves as futex trylock_pi()'ing, and due semantics.
+ */
+int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int trylock)
+{
+ struct hrtimer_sleeper timeout, *to;
+ struct task_struct *exiting = NULL;
+ struct rt_mutex_waiter rt_waiter;
+ struct futex_hash_bucket *hb;
+ struct futex_q q = futex_q_init;
+ int res, ret;
+
+ if (!IS_ENABLED(CONFIG_FUTEX_PI))
+ return -ENOSYS;
+
+ if (refill_pi_state_cache())
+ return -ENOMEM;
+
+ to = futex_setup_timer(time, &timeout, flags, 0);
+
+retry:
+ ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE);
+ if (unlikely(ret != 0))
+ goto out;
+
+retry_private:
+ hb = futex_q_lock(&q);
+
+ ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current,
+ &exiting, 0);
+ if (unlikely(ret)) {
+ /*
+ * Atomic work succeeded and we got the lock,
+ * or failed. Either way, we do _not_ block.
+ */
+ switch (ret) {
+ case 1:
+ /* We got the lock. */
+ ret = 0;
+ goto out_unlock_put_key;
+ case -EFAULT:
+ goto uaddr_faulted;
+ case -EBUSY:
+ case -EAGAIN:
+ /*
+ * Two reasons for this:
+ * - EBUSY: Task is exiting and we just wait for the
+ * exit to complete.
+ * - EAGAIN: The user space value changed.
+ */
+ futex_q_unlock(hb);
+ /*
+ * Handle the case where the owner is in the middle of
+ * exiting. Wait for the exit to complete otherwise
+ * this task might loop forever, aka. live lock.
+ */
+ wait_for_owner_exiting(ret, exiting);
+ cond_resched();
+ goto retry;
+ default:
+ goto out_unlock_put_key;
+ }
+ }
+
+ WARN_ON(!q.pi_state);
+
+ /*
+ * Only actually queue now that the atomic ops are done:
+ */
+ __futex_queue(&q, hb);
+
+ if (trylock) {
+ ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
+ /* Fixup the trylock return value: */
+ ret = ret ? 0 : -EWOULDBLOCK;
+ goto no_block;
+ }
+
+ rt_mutex_init_waiter(&rt_waiter);
+
+ /*
+ * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
+ * hold it while doing rt_mutex_start_proxy(), because then it will
+ * include hb->lock in the blocking chain, even through we'll not in
+ * fact hold it while blocking. This will lead it to report -EDEADLK
+ * and BUG when futex_unlock_pi() interleaves with this.
+ *
+ * Therefore acquire wait_lock while holding hb->lock, but drop the
+ * latter before calling __rt_mutex_start_proxy_lock(). This
+ * interleaves with futex_unlock_pi() -- which does a similar lock
+ * handoff -- such that the latter can observe the futex_q::pi_state
+ * before __rt_mutex_start_proxy_lock() is done.
+ */
+ raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
+ spin_unlock(q.lock_ptr);
+ /*
+ * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
+ * such that futex_unlock_pi() is guaranteed to observe the waiter when
+ * it sees the futex_q::pi_state.
+ */
+ ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
+ raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
+
+ if (ret) {
+ if (ret == 1)
+ ret = 0;
+ goto cleanup;
+ }
+
+ if (unlikely(to))
+ hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS);
+
+ ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
+
+cleanup:
+ spin_lock(q.lock_ptr);
+ /*
+ * If we failed to acquire the lock (deadlock/signal/timeout), we must
+ * first acquire the hb->lock before removing the lock from the
+ * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
+ * lists consistent.
+ *
+ * In particular; it is important that futex_unlock_pi() can not
+ * observe this inconsistency.
+ */
+ if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
+ ret = 0;
+
+no_block:
+ /*
+ * Fixup the pi_state owner and possibly acquire the lock if we
+ * haven't already.
+ */
+ res = fixup_pi_owner(uaddr, &q, !ret);
+ /*
+ * If fixup_pi_owner() returned an error, propagate that. If it acquired
+ * the lock, clear our -ETIMEDOUT or -EINTR.
+ */
+ if (res)
+ ret = (res < 0) ? res : 0;
+
+ futex_unqueue_pi(&q);
+ spin_unlock(q.lock_ptr);
+ goto out;
+
+out_unlock_put_key:
+ futex_q_unlock(hb);
+
+out:
+ if (to) {
+ hrtimer_cancel(&to->timer);
+ destroy_hrtimer_on_stack(&to->timer);
+ }
+ return ret != -EINTR ? ret : -ERESTARTNOINTR;
+
+uaddr_faulted:
+ futex_q_unlock(hb);
+
+ ret = fault_in_user_writeable(uaddr);
+ if (ret)
+ goto out;
+
+ if (!(flags & FLAGS_SHARED))
+ goto retry_private;
+
+ goto retry;
+}
+
+/*
+ * Userspace attempted a TID -> 0 atomic transition, and failed.
+ * This is the in-kernel slowpath: we look up the PI state (if any),
+ * and do the rt-mutex unlock.
+ */
+int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
+{
+ u32 curval, uval, vpid = task_pid_vnr(current);
+ union futex_key key = FUTEX_KEY_INIT;
+ struct futex_hash_bucket *hb;
+ struct futex_q *top_waiter;
+ int ret;
+
+ if (!IS_ENABLED(CONFIG_FUTEX_PI))
+ return -ENOSYS;
+
+retry:
+ if (get_user(uval, uaddr))
+ return -EFAULT;
+ /*
+ * We release only a lock we actually own:
+ */
+ if ((uval & FUTEX_TID_MASK) != vpid)
+ return -EPERM;
+
+ ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE);
+ if (ret)
+ return ret;
+
+ hb = futex_hash(&key);
+ spin_lock(&hb->lock);
+
+ /*
+ * Check waiters first. We do not trust user space values at
+ * all and we at least want to know if user space fiddled
+ * with the futex value instead of blindly unlocking.
+ */
+ top_waiter = futex_top_waiter(hb, &key);
+ if (top_waiter) {
+ struct futex_pi_state *pi_state = top_waiter->pi_state;
+
+ ret = -EINVAL;
+ if (!pi_state)
+ goto out_unlock;
+
+ /*
+ * If current does not own the pi_state then the futex is
+ * inconsistent and user space fiddled with the futex value.
+ */
+ if (pi_state->owner != current)
+ goto out_unlock;
+
+ get_pi_state(pi_state);
+ /*
+ * By taking wait_lock while still holding hb->lock, we ensure
+ * there is no point where we hold neither; and therefore
+ * wake_futex_p() must observe a state consistent with what we
+ * observed.
+ *
+ * In particular; this forces __rt_mutex_start_proxy() to
+ * complete such that we're guaranteed to observe the
+ * rt_waiter. Also see the WARN in wake_futex_pi().
+ */
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+ spin_unlock(&hb->lock);
+
+ /* drops pi_state->pi_mutex.wait_lock */
+ ret = wake_futex_pi(uaddr, uval, pi_state);
+
+ put_pi_state(pi_state);
+
+ /*
+ * Success, we're done! No tricky corner cases.
+ */
+ if (!ret)
+ return ret;
+ /*
+ * The atomic access to the futex value generated a
+ * pagefault, so retry the user-access and the wakeup:
+ */
+ if (ret == -EFAULT)
+ goto pi_faulted;
+ /*
+ * A unconditional UNLOCK_PI op raced against a waiter
+ * setting the FUTEX_WAITERS bit. Try again.
+ */
+ if (ret == -EAGAIN)
+ goto pi_retry;
+ /*
+ * wake_futex_pi has detected invalid state. Tell user
+ * space.
+ */
+ return ret;
+ }
+
+ /*
+ * We have no kernel internal state, i.e. no waiters in the
+ * kernel. Waiters which are about to queue themselves are stuck
+ * on hb->lock. So we can safely ignore them. We do neither
+ * preserve the WAITERS bit not the OWNER_DIED one. We are the
+ * owner.
+ */
+ if ((ret = futex_cmpxchg_value_locked(&curval, uaddr, uval, 0))) {
+ spin_unlock(&hb->lock);
+ switch (ret) {
+ case -EFAULT:
+ goto pi_faulted;
+
+ case -EAGAIN:
+ goto pi_retry;
+
+ default:
+ WARN_ON_ONCE(1);
+ return ret;
+ }
+ }
+
+ /*
+ * If uval has changed, let user space handle it.
+ */
+ ret = (curval == uval) ? 0 : -EAGAIN;
+
+out_unlock:
+ spin_unlock(&hb->lock);
+ return ret;
+
+pi_retry:
+ cond_resched();
+ goto retry;
+
+pi_faulted:
+
+ ret = fault_in_user_writeable(uaddr);
+ if (!ret)
+ goto retry;
+
+ return ret;
+}
+
|