Messages in this thread Patch in this message | | | Subject | Re: [PATCH] sched: fix rt_nr_migratory corruption raised in push_rt_task() | From | Mike Galbraith <> | Date | Tue, 31 May 2011 09:36:37 +0200 |
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On Mon, 2011-05-30 at 21:39 +0800, Hillf Danton wrote: > When pushing, if a pushable task could not be pushed, it is dequeued with no > updating the rt_nr_migratory element of RT run-queue, then rt_nr_migratory is > corrupted, which is fixed by removing the dequeue operation.
Hm. I think you're right that this dequeue_pushable_task() call can be removed, at least I didn't see it's reason for existing. I'd word it a bit differently though, and not return 1 unless we really did push.
From: Hillf Danton <dhillf@gmail.com>
sched, rt: fix rq->rt.pushable_tasks bug in push_rt_task()
Do not call dequeue_pushable_task() when failing to push an eligible task, as it remains pushable, merely not at this particular moment.
Signed-off-by: Hillf Danton <dhillf@gmail.com> --- kernel/sched_rt.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-)
Index: linux-2.6.40.git/kernel/sched_rt.c =================================================================== --- linux-2.6.40.git.orig/kernel/sched_rt.c +++ linux-2.6.40.git/kernel/sched_rt.c @@ -1378,6 +1378,7 @@ static int push_rt_task(struct rq *rq) { struct task_struct *next_task; struct rq *lowest_rq; + int ret = 0; if (!rq->rt.overloaded) return 0; @@ -1410,7 +1411,7 @@ retry: if (!lowest_rq) { struct task_struct *task; /* - * find lock_lowest_rq releases rq->lock + * find_lock_lowest_rq releases rq->lock * so it is possible that next_task has migrated. * * We need to make sure that the task is still on the same @@ -1420,12 +1421,11 @@ retry: task = pick_next_pushable_task(rq); if (task_cpu(next_task) == rq->cpu && task == next_task) { /* - * If we get here, the task hasn't moved at all, but - * it has failed to push. We will not try again, - * since the other cpus will pull from us when they - * are ready. + * The task hasn't migrated, and is still the next + * eligible task, but we failed to find a run-queue + * to push it to. Do not retry in this case, since + * other cpus will pull from us when ready. */ - dequeue_pushable_task(rq, next_task); goto out; } @@ -1444,6 +1444,7 @@ retry: deactivate_task(rq, next_task, 0); set_task_cpu(next_task, lowest_rq->cpu); activate_task(lowest_rq, next_task, 0); + ret = 1; resched_task(lowest_rq->curr); @@ -1452,7 +1453,7 @@ retry: out: put_task_struct(next_task); - return 1; + return ret; } static void push_rt_tasks(struct rq *rq)
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