[PATCH] os: Fix timer race conditions

[Nikhil Mahale]

On Monday, November 24, 2014 10:52:37 PM Julien Cristau wrote:
> 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?
> 

ok, here is updated patch.

> Cheers,
> Julien

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