ipc/sem: revert ipc/sem: Rework semaphore wakeups
Revert Peterz's -rt wakeup scheme to prepare for replacement with a new
completion scheme by Manfred Spraul.
<original changelog>
ipc/sem: Rework semaphore wakeups
Current sysv sems have a weird ass wakeup scheme that involves keeping
preemption disabled over a potential O(n^2) loop and busy waiting on
that on other CPUs.
Kill this and simply wake the task directly from under the sem_lock.
This was discovered by a migrate_disable() debug feature that
disallows:
spin_lock();
preempt_disable();
spin_unlock()
preempt_enable();
</original changelog>
Signed-off-by: Mike Galbraith <bitbucket@xxxxxxxxx>
---
ipc/sem.c | 24 +++++++-----------------
1 file changed, 7 insertions(+), 17 deletions(-)
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -155,7 +155,7 @@ static int sysvipc_sem_proc_show(struct
* sem_array.sem_pending{,last},
* sem_array.sem_undo: sem_lock() for read/write
* sem_undo.proc_next: only "current" is allowed to read/write that field.
- *
+ *
*/
#define sc_semmsl sem_ctls[0]
@@ -518,7 +518,7 @@ static int try_atomic_semop (struct sem_
curr = sma->sem_base + sop->sem_num;
sem_op = sop->sem_op;
result = curr->semval;
-
+
if (!sem_op && result)
goto would_block;
@@ -545,7 +545,7 @@ static int try_atomic_semop (struct sem_
un->semadj[sop->sem_num] -= sop->sem_op;
sop--;
}
-
+
return 0;
out_of_range:
@@ -577,13 +577,6 @@ static int try_atomic_semop (struct sem_
static void wake_up_sem_queue_prepare(struct list_head *pt,
struct sem_queue *q, int error)
{
-#ifdef CONFIG_PREEMPT_RT_BASE
- struct task_struct *p = q->sleeper;
- get_task_struct(p);
- q->status = error;
- wake_up_process(p);
- put_task_struct(p);
-#else
if (list_empty(pt)) {
/*
* Hold preempt off so that we don't get preempted and have the
@@ -595,7 +588,6 @@ static void wake_up_sem_queue_prepare(st
q->pid = error;
list_add_tail(&q->list, pt);
-#endif
}
/**
@@ -609,7 +601,6 @@ static void wake_up_sem_queue_prepare(st
*/
static void wake_up_sem_queue_do(struct list_head *pt)
{
-#ifndef CONFIG_PREEMPT_RT_BASE
struct sem_queue *q, *t;
int did_something;
@@ -622,7 +613,6 @@ static void wake_up_sem_queue_do(struct
}
if (did_something)
preempt_enable();
-#endif
}
static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
@@ -977,7 +967,7 @@ static int semctl_nolock(struct ipc_name
err = security_sem_semctl(NULL, cmd);
if (err)
return err;
-
+
memset(&seminfo,0,sizeof(seminfo));
seminfo.semmni = ns->sc_semmni;
seminfo.semmns = ns->sc_semmns;
@@ -997,7 +987,7 @@ static int semctl_nolock(struct ipc_name
}
max_id = ipc_get_maxid(&sem_ids(ns));
up_read(&sem_ids(ns).rw_mutex);
- if (copy_to_user(p, &seminfo, sizeof(struct seminfo)))
+ if (copy_to_user(p, &seminfo, sizeof(struct seminfo)))
return -EFAULT;
return (max_id < 0) ? 0: max_id;
}
@@ -1672,7 +1662,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid,
/* We need to sleep on this operation, so we put the current
* task into the pending queue and go to sleep.
*/
-
+
queue.sops = sops;
queue.nsops = nsops;
queue.undo = un;
@@ -1795,7 +1785,7 @@ int copy_semundo(unsigned long clone_fla
return error;
atomic_inc(&undo_list->refcnt);
tsk->sysvsem.undo_list = undo_list;
- } else
+ } else
tsk->sysvsem.undo_list = NULL;
return 0;
--
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