3.9-stable review patch. If anyone has any objections, please let me know.
------------------ From: Imre Deak <[email protected]> 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 <[email protected]> Acked-by: Daniel Vetter <[email protected]> Acked-by: David Howells <[email protected]> Acked-by: Jens Axboe <[email protected]> Cc: "Paul E. McKenney" <[email protected]> Cc: Dave Jones <[email protected]> Cc: Lukas Czerner <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- include/linux/wait.h | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) --- 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) \ ({ \ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
