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>

1 files changed, 6 insertions, 4 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index ff39cadf621e..8b3532f262d7 100644
--- 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);