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authorOleg Nesterov <oleg@redhat.com>2013-08-12 18:14:00 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-01-09 12:24:23 -0800
commit57f74b6ecebf59991677dd2da0f0433e8be6c945 (patch)
tree4e3b332c34f41796e61bf7bcfb3e6bb06386e0b3 /kernel
parenta29ccdd1b5a61fad7d4883b3ef63da3a313f1e44 (diff)
downloadlinaro-lsk-57f74b6ecebf59991677dd2da0f0433e8be6c945.tar.gz
sched: fix the theoretical signal_wake_up() vs schedule() race
commit e0acd0a68ec7dbf6b7a81a87a867ebd7ac9b76c4 upstream. This is only theoretical, but after try_to_wake_up(p) was changed to check p->state under p->pi_lock the code like __set_current_state(TASK_INTERRUPTIBLE); schedule(); can miss a signal. This is the special case of wait-for-condition, it relies on try_to_wake_up/schedule interaction and thus it does not need mb() between __set_current_state() and if(signal_pending). However, this __set_current_state() can move into the critical section protected by rq->lock, now that try_to_wake_up() takes another lock we need to ensure that it can't be reordered with "if (signal_pending(current))" check inside that section. The patch is actually one-liner, it simply adds smp_wmb() before spin_lock_irq(rq->lock). This is what try_to_wake_up() already does by the same reason. We turn this wmb() into the new helper, smp_mb__before_spinlock(), for better documentation and to allow the architectures to change the default implementation. While at it, kill smp_mb__after_lock(), it has no callers. Perhaps we can also add smp_mb__before/after_spinunlock() for prepare_to_wait(). Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/core.c14
1 files changed, 13 insertions, 1 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e8b335016c5..f9e35b1e771 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1487,7 +1487,13 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
unsigned long flags;
int cpu, success = 0;
- smp_wmb();
+ /*
+ * If we are going to wake up a thread waiting for CONDITION we
+ * need to ensure that CONDITION=1 done by the caller can not be
+ * reordered with p->state check below. This pairs with mb() in
+ * set_current_state() the waiting thread does.
+ */
+ smp_mb__before_spinlock();
raw_spin_lock_irqsave(&p->pi_lock, flags);
if (!(p->state & state))
goto out;
@@ -2966,6 +2972,12 @@ need_resched:
if (sched_feat(HRTICK))
hrtick_clear(rq);
+ /*
+ * Make sure that signal_pending_state()->signal_pending() below
+ * can't be reordered with __set_current_state(TASK_INTERRUPTIBLE)
+ * done by the caller to avoid the race with signal_wake_up().
+ */
+ smp_mb__before_spinlock();
raw_spin_lock_irq(&rq->lock);
switch_count = &prev->nivcsw;