sched: Make wakeup side and atomic variants of completion API irq safe

Alan Stern noticed that all the wakeup side (and atomic) variants of the
completion APIs should be irq safe, but the newly introduced
completion_done() and try_wait_for_completion() aren't. The use of the
irq unsafe variants in IRQ contexts can cause crashes/hangs.

Fix the problem by making them use spin_lock_irqsave() and
spin_lock_irqrestore().

Reported-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: pm list <linux-pm@lists.linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: David Chinner <david@fromorbit.com>
Cc: Lachlan McIlroy <lachlan@sgi.com>
LKML-Reference: <200912130007.30541.rjw@sisk.pl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched.c b/kernel/sched.c
index ff39cadf621e91834dcdc9116d123f8912eab225..8b3532f262d70bc7a5a306f41efa3e3ba95f253e 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5908,14 +5908,15 @@ EXPORT_SYMBOL(wait_for_completion_killable);
  */
 bool try_wait_for_completion(struct completion *x)
 {
+       unsigned long flags;
        int ret = 1;
 
-       spin_lock_irq(&x->wait.lock);
+       spin_lock_irqsave(&x->wait.lock, flags);
        if (!x->done)
                ret = 0;
        else
                x->done--;
-       spin_unlock_irq(&x->wait.lock);
+       spin_unlock_irqrestore(&x->wait.lock, flags);
        return ret;
 }
 EXPORT_SYMBOL(try_wait_for_completion);
@@ -5930,12 +5931,13 @@ EXPORT_SYMBOL(try_wait_for_completion);
  */
 bool completion_done(struct completion *x)
 {
+       unsigned long flags;
        int ret = 1;
 
-       spin_lock_irq(&x->wait.lock);
+       spin_lock_irqsave(&x->wait.lock, flags);
        if (!x->done)
                ret = 0;
-       spin_unlock_irq(&x->wait.lock);
+       spin_unlock_irqrestore(&x->wait.lock, flags);
        return ret;
 }
 EXPORT_SYMBOL(completion_done);