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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2011-09-13 15:09:40 +0200
committerClark Williams <williams@redhat.com>2012-02-15 10:33:02 -0600
commit3893956d052410c6da459c1cdddd92a673d349c9 (patch)
tree208ab16bb5879a685aa6a19080f9ec37d0683d21
parent32aea8bf12ebc86c28091b0353d597ac144b47a1 (diff)
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(); Cc: Manfred Spraul <manfred@colorfullife.com> Suggested-by: Thomas Gleixner <tglx@linutronix.de> Reported-by: Mike Galbraith <efault@gmx.de> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Manfred Spraul <manfred@colorfullife.com> Link: http://lkml.kernel.org/r/1315994224.5040.1.camel@twins Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
-rw-r--r--ipc/sem.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/ipc/sem.c b/ipc/sem.c
index 5215a81420df..5eaf6846d8cd 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -461,6 +461,13 @@ undo:
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
@@ -472,6 +479,7 @@ static void wake_up_sem_queue_prepare(struct list_head *pt,
q->pid = error;
list_add_tail(&q->simple_list, pt);
+#endif
}
/**
@@ -485,6 +493,7 @@ static void wake_up_sem_queue_prepare(struct list_head *pt,
*/
static void wake_up_sem_queue_do(struct list_head *pt)
{
+#ifndef CONFIG_PREEMPT_RT_BASE
struct sem_queue *q, *t;
int did_something;
@@ -497,6 +506,7 @@ static void wake_up_sem_queue_do(struct list_head *pt)
}
if (did_something)
preempt_enable();
+#endif
}
static void unlink_queue(struct sem_array *sma, struct sem_queue *q)