The following commit has been merged into the locking/core branch of tip:
Commit-ID: 9321f8152d9a764208c3f0dad49e0c55f293b7ab
Gitweb: https://git.kernel.org/tip/9321f8152d9a764208c3f0dad49e0c55f293b7ab
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Tue, 28 Sep 2021 17:00:06 +02:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Fri, 01 Oct 2021 13:57:52 +02:00
rtmutex: Wake up the waiters lockless while dropping the read lock.
The rw_semaphore and rwlock_t implementation both wake the waiter while
holding the rt_mutex_base::wait_lock acquired.
This can be optimized by waking the waiter lockless outside of the
locked section to avoid a needless contention on the
rt_mutex_base::wait_lock lock.
Extend rt_mutex_wake_q_add() to also accept task and state and use it in
__rwbase_read_unlock().
Suggested-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20210928150006.597310-3-bigeasy@xxxxxxxxxxxxx
---
kernel/locking/rtmutex.c | 19 +++++++++++++------
kernel/locking/rwbase_rt.c | 6 +++++-
2 files changed, 18 insertions(+), 7 deletions(-)
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index cafc259..0c6a48d 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -446,19 +446,26 @@ static __always_inline void rt_mutex_adjust_prio(struct task_struct *p)
}
/* RT mutex specific wake_q wrappers */
-static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh,
- struct rt_mutex_waiter *w)
+static __always_inline void rt_mutex_wake_q_add_task(struct rt_wake_q_head *wqh,
+ struct task_struct *task,
+ unsigned int wake_state)
{
- if (IS_ENABLED(CONFIG_PREEMPT_RT) && w->wake_state == TASK_RTLOCK_WAIT) {
+ if (IS_ENABLED(CONFIG_PREEMPT_RT) && wake_state == TASK_RTLOCK_WAIT) {
if (IS_ENABLED(CONFIG_PROVE_LOCKING))
WARN_ON_ONCE(wqh->rtlock_task);
- get_task_struct(w->task);
- wqh->rtlock_task = w->task;
+ get_task_struct(task);
+ wqh->rtlock_task = task;
} else {
- wake_q_add(&wqh->head, w->task);
+ wake_q_add(&wqh->head, task);
}
}
+static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh,
+ struct rt_mutex_waiter *w)
+{
+ rt_mutex_wake_q_add_task(wqh, w->task, w->wake_state);
+}
+
static __always_inline void rt_mutex_wake_up_q(struct rt_wake_q_head *wqh)
{
if (IS_ENABLED(CONFIG_PREEMPT_RT) && wqh->rtlock_task) {
diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c
index 4ba1508..6b143fb 100644
--- a/kernel/locking/rwbase_rt.c
+++ b/kernel/locking/rwbase_rt.c
@@ -141,6 +141,7 @@ static void __sched __rwbase_read_unlock(struct rwbase_rt *rwb,
{
struct rt_mutex_base *rtm = &rwb->rtmutex;
struct task_struct *owner;
+ DEFINE_RT_WAKE_Q(wqh);
raw_spin_lock_irq(&rtm->wait_lock);
/*
@@ -151,9 +152,12 @@ static void __sched __rwbase_read_unlock(struct rwbase_rt *rwb,
*/
owner = rt_mutex_owner(rtm);
if (owner)
- wake_up_state(owner, state);
+ rt_mutex_wake_q_add_task(&wqh, owner, state);
+ /* Pairs with the preempt_enable in rt_mutex_wake_up_q() */
+ preempt_disable();
raw_spin_unlock_irq(&rtm->wait_lock);
+ rt_mutex_wake_up_q(&wqh);
}
static __always_inline void rwbase_read_unlock(struct rwbase_rt *rwb,
|