On Tue, May 20, 2014 at 01:33:42PM +0400, Kirill Tkhai wrote: > [PATCH] sched/dl: Fix race in dl_task_timer() > > Throttled task is still on rq, and it may be moved to other cpu > if user is playing with sched_setaffinity(). Therefore, unlocked > task_rq() access makes the race. > > Juri Lelli reports he got this race when dl_bandwidth_enabled() > was not set. > > Other thing, pointed by Peter Zijlstra: > > "Now I suppose the problem can still actually happen when > you change the root domain and trigger a effective affinity > change that way". > > To fix that we do the same as made in __task_rq_lock(). We do not > use __task_rq_lock() itself, because it has a useful lockdep check, > which is not correct in case of dl_task_timer(). We do not need > pi_lock locked here. This case is an exception (PeterZ): > > "The only reason we don't strictly need ->pi_lock now is because > we're guaranteed to have p->state == TASK_RUNNING here and are > thus free of ttwu races". > > Signed-off-by: Kirill Tkhai <tkhai@xxxxxxxxx> > CC: Juri Lelli <juri.lelli@xxxxxxxxx> > CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > CC: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> # v3.14 > --- thanks Kirill!
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