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author | Peter Zijlstra <peterz@infradead.org> | 2014-02-14 12:25:08 +0100 |
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committer | Ingo Molnar <mingo@kernel.org> | 2014-02-27 12:41:02 +0100 |
commit | 37e117c07b89194aae7062bc63bde1104c03db02 (patch) | |
tree | 770312bf789e367b8f2102e9f8de743f05efeeac /kernel/sched/rt.c | |
parent | 06d50c65b1043b166d102accc081093f79d8f7e5 (diff) | |
download | linux-37e117c07b89194aae7062bc63bde1104c03db02.tar.gz |
sched: Guarantee task priority in pick_next_task()
Michael spotted that the idle_balance() push down created a task priority problem. Previously, when we called idle_balance() before pick_next_task() it wasn't a problem when -- because of the rq->lock droppage -- an rt/dl task slipped in. Similarly for pre_schedule(), rt pre-schedule could have a dl task slip in. But by pulling it into the pick_next_task() loop, we'll not try a higher task priority again. Cure this by creating a re-start condition in pick_next_task(); and triggering this from pick_next_task_{rt,fair}(). It also fixes a live-lock where we get stuck in pick_next_task_fair() due to idle_balance() seeing !0 nr_running but there not actually being any fair tasks about. Reported-by: Michael Wang <wangyun@linux.vnet.ibm.com> Fixes: 38033c37faab ("sched: Push down pre_schedule() and idle_balance()") Tested-by: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Juri Lelli <juri.lelli@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Link: http://lkml.kernel.org/r/20140224121218.GR15586@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched/rt.c')
-rw-r--r-- | kernel/sched/rt.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 4d4b386598aa..398b3f990823 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1360,8 +1360,16 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev) struct task_struct *p; struct rt_rq *rt_rq = &rq->rt; - if (need_pull_rt_task(rq, prev)) + if (need_pull_rt_task(rq, prev)) { pull_rt_task(rq); + /* + * pull_rt_task() can drop (and re-acquire) rq->lock; this + * means a dl task can slip in, in which case we need to + * re-start task selection. + */ + if (unlikely(rq->dl.dl_nr_running)) + return RETRY_TASK; + } if (!rt_rq->rt_nr_running) return NULL; |