From: Oleg Nesterov Date: Mon, 15 Mar 2010 09:10:10 +0000 (+0100) Subject: sched: move_task_off_dead_cpu(): Take rq->lock around select_fallback_rq() X-Git-Tag: v2.6.35-rc1~521^2~27 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1445c08d06c5594895b4fae952ef8a457e89c390;p=pandora-kernel.git sched: move_task_off_dead_cpu(): Take rq->lock around select_fallback_rq() move_task_off_dead_cpu()->select_fallback_rq() reads/updates ->cpus_allowed lockless. We can race with set_cpus_allowed() running in parallel. Change it to take rq->lock around select_fallback_rq(). Note that it is not trivial to move this spin_lock() into select_fallback_rq(), we must recheck the task was not migrated after we take the lock and other callers do not need this lock. To avoid the races with other callers of select_fallback_rq() which rely on TASK_WAKING, we also check p->state != TASK_WAKING and do nothing otherwise. The owner of TASK_WAKING must update ->cpus_allowed and choose the correct CPU anyway, and the subsequent __migrate_task() is just meaningless because p->se.on_rq must be false. Alternatively, we could change select_task_rq() to take rq->lock right after it calls sched_class->select_task_rq(), but this looks a bit ugly. Also, change it to not assume irqs are disabled and absorb __migrate_task_irq(). Signed-off-by: Oleg Nesterov Signed-off-by: Peter Zijlstra LKML-Reference: <20100315091010.GA9131@redhat.com> Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed