From: Kirill Tkhai Date: Tue, 20 May 2014 09:33:42 +0000 (+0400) Subject: sched/dl: Fix race in dl_task_timer() X-Git-Tag: omap-for-v3.16/fixes-against-rc1~98^2~1 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0f397f2c90ce68821ee864c2c53baafe78de765d;p=pandora-kernel.git 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 Signed-off-by: Peter Zijlstra Cc: # v3.14+ Cc: Linus Torvalds Link: http://lkml.kernel.org/r/3056991400578422@web14g.yandex.ru Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed