Patchwork [3.8.y.z,extended,stable] Patch "wait: fix false timeouts when using wait_event_timeout()" has been added to staging queue

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Submitter Kamal Mostafa
Date May 30, 2013, 8:34 p.m.
Message ID <1369946095-12843-1-git-send-email-kamal@canonical.com>
Download mbox | patch
Permalink /patch/247913/
State New
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Comments

Kamal Mostafa - May 30, 2013, 8:34 p.m.
This is a note to let you know that I have just added a patch titled

    wait: fix false timeouts when using wait_event_timeout()

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

From a870c27bde09d40caf2890b9aa5cc508c7a3d0ad Mon Sep 17 00:00:00 2001
From: Imre Deak <imre.deak@intel.com>
Date: Fri, 24 May 2013 15:55:09 -0700
Subject: wait: fix false timeouts when using wait_event_timeout()

commit 4c663cfc523a88d97a8309b04a089c27dc57fd7e upstream.

Many callers of the wait_event_timeout() and
wait_event_interruptible_timeout() expect that the return value will be
positive if the specified condition becomes true before the timeout
elapses.  However, at the moment this isn't guaranteed.  If the wake-up
handler is delayed enough, the time remaining until timeout will be
calculated as 0 - and passed back as a return value - even if the
condition became true before the timeout has passed.

Fix this by returning at least 1 if the condition becomes true.  This
semantic is in line with what wait_for_condition_timeout() does; see
commit bb10ed09 ("sched: fix wait_for_completion_timeout() spurious
failure under heavy load").

Daniel said "We have 3 instances of this bug in drm/i915.  One case even
where we switch between the interruptible and not interruptible
wait_event_timeout variants, foolishly presuming they have the same
semantics.  I very much like this."

One such bug is reported at
  https://bugs.freedesktop.org/show_bug.cgi?id=64133

Signed-off-by: Imre Deak <imre.deak@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: David Howells <dhowells@redhat.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Cc: "Paul E.  McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 include/linux/wait.h | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

--
1.8.1.2

Patch

diff --git a/include/linux/wait.h b/include/linux/wait.h
index 7cb64d4..30194a6 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -217,6 +217,8 @@  do {									\
 		if (!ret)						\
 			break;						\
 	}								\
+	if (!ret && (condition))					\
+		ret = 1;						\
 	finish_wait(&wq, &__wait);					\
 } while (0)

@@ -233,8 +235,9 @@  do {									\
  * wake_up() has to be called after changing any variable that could
  * change the result of the wait condition.
  *
- * The function returns 0 if the @timeout elapsed, and the remaining
- * jiffies if the condition evaluated to true before the timeout elapsed.
+ * The function returns 0 if the @timeout elapsed, or the remaining
+ * jiffies (at least 1) if the @condition evaluated to %true before
+ * the @timeout elapsed.
  */
 #define wait_event_timeout(wq, condition, timeout)			\
 ({									\
@@ -302,6 +305,8 @@  do {									\
 		ret = -ERESTARTSYS;					\
 		break;							\
 	}								\
+	if (!ret && (condition))					\
+		ret = 1;						\
 	finish_wait(&wq, &__wait);					\
 } while (0)

@@ -318,9 +323,10 @@  do {									\
  * wake_up() has to be called after changing any variable that could
  * change the result of the wait condition.
  *
- * The function returns 0 if the @timeout elapsed, -ERESTARTSYS if it
- * was interrupted by a signal, and the remaining jiffies otherwise
- * if the condition evaluated to true before the timeout elapsed.
+ * Returns:
+ * 0 if the @timeout elapsed, -%ERESTARTSYS if it was interrupted by
+ * a signal, or the remaining jiffies (at least 1) if the @condition
+ * evaluated to %true before the @timeout elapsed.
  */
 #define wait_event_interruptible_timeout(wq, condition, timeout)	\
 ({									\