From: Julien Desfossez Date: Fri, 16 Sep 2016 16:16:36 +0000 (-0400) Subject: sched/fair: check_preempt_wakeup: Fix assumption on the default policy X-Git-Url: http://git.efficios.com/?p=deliverable%2Flinux.git;a=commitdiff_plain;h=f14bf141e6378d6176bc23e2509f2535e8a0aae7 sched/fair: check_preempt_wakeup: Fix assumption on the default policy Tasks with RT or deadline scheduling class may inherit from a task with a "fair" scheduling class. This priority inheritance changes the scheduling class, but not the task "policy" field. Therefore, the fair scheduler should not assume that policy != SCHED_NORMAL is the same as (policy == SCHED_BATCH || policy == SCHED_IDLE), because the policy could also be SCHED_RR, SCHED_FIFO, or SCHED_DEADLINE. The incorrect comparison in check_preempt_wakeup makes RR, FIFO and DEADLINE tasks which inherit from a fair task behave as if they were IDLE or BATCH tasks, thus awaiting the following tick before preempting the current task. Cc: Peter Zijlstra Cc: Steven Rostedt (Red Hat) Cc: Thomas Gleixner Cc: Ingo Molnar Signed-off-by: Mathieu Desnoyers Signed-off-by: Julien Desfossez --- diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 07aaa7f08597..f3aef2108368 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5669,7 +5669,8 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_ * Batch and idle tasks do not preempt non-idle tasks (their preemption * is driven by the tick): */ - if (unlikely(p->policy != SCHED_NORMAL) || !sched_feat(WAKEUP_PREEMPTION)) + if (unlikely(p->policy == SCHED_BATCH || p->policy == SCHED_IDLE) || + !sched_feat(WAKEUP_PREEMPTION)) return; find_matching_se(&se, &pse);