[PATCH] os: Fix timer race conditions

[Julien Cristau]

On Fri, Nov 14, 2014 at 23:52:55 +0530, Nikhil Mahale wrote:


> From 40f5100cb73aad8f90ba2c926dd08c4e15789de0 Mon Sep 17 00:00:00 2001
> From: Nikhil Mahale <nmahale at nvidia.com>
> Date: Tue, 11 Nov 2014 17:44:28 +0530
> Subject: [PATCH] os: Fix timer race conditions
> 
> Fixing following kind of race-conditions -
> 
>     WaitForSomething()
>     |
>     ---->  // timers -> timer-1 -> timer-2 -> null
>            while (timers && (int) (timers->expires - now) <= 0)
>                // prototype - DoTimer(OsTimerPtr timer, CARD32 now, OsTimerPtr *prev)
>                DoTimer(timers, now, &timers)
>                |
>                |
>                ----> OsBlockSignals();  .... OS Signal comes just before blocking it,
>                                         .... timer-1 handler gets called.
>                                              // timer-1 gets served and scheduled again;
>                                              // timers -> timer-2 -> timer-1 -> null
>                                         ....
>                      *prev = timer->next;
>                       timer->next = NULL;   // timers -> null
>                       // timers list gets corrupted here and timer-2 gets removed from list.
> 
> https://bugs.freedesktop.org/show_bug.cgi?id=86288
> Signed-off-by: Nikhil Mahale <nmahale at nvidia.com>
> ---
>  os/WaitFor.c | 31 +++++++++++++++++++++----------
>  1 file changed, 21 insertions(+), 10 deletions(-)
> 
As far as I can tell after this change DoTimer is always called with
signals disabled, so it doesn't need to disable them itself?

Cheers,
Julien