From 8c5217d732d576bcdacf7cd515165f246e6a4912 Mon Sep 17 00:00:00 2001 From: Mike Galbraith Date: Thu, 26 Aug 2010 05:29:16 +0200 Subject: [PATCH] sched: revert stable c6fc81a sched: Fix a race between ttwu() and migrate_task() This commit does not appear to have been meant for 32-stable, and causes ltp's cpusets testcases to fail, revert it. Original commit text: sched: Fix a race between ttwu() and migrate_task() Based on commit e2912009fb7b715728311b0d8fe327a1432b3f79 upstream, but done differently as this issue is not present in .33 or .34 kernels due to rework in this area. If a task is in the TASK_WAITING state, then try_to_wake_up() is working on it, and it will place it on the correct cpu. This commit ensures that neither migrate_task() nor __migrate_task() calls set_task_cpu(p) while p is in the TASK_WAKING state. Otherwise, there could be two concurrent calls to set_task_cpu(p), resulting in the task's cfs_rq being inconsistent with its cpu. Signed-off-by: Mike Galbraith Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Greg Kroah-Hartman --- kernel/sched.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index ba2d610f4529..48f8dc07648d 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2123,10 +2123,12 @@ migrate_task(struct task_struct *p, int dest_cpu, struct migration_req *req) /* * If the task is not on a runqueue (and not running), then - * the next wake-up will properly place the task. + * it is sufficient to simply update the task's cpu field. */ - if (!p->se.on_rq && !task_running(rq, p)) + if (!p->se.on_rq && !task_running(rq, p)) { + set_task_cpu(p, dest_cpu); return 0; + } init_completion(&req->done); req->task = p; @@ -7217,9 +7219,6 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu) /* Already moved. */ if (task_cpu(p) != src_cpu) goto done; - /* Waking up, don't get in the way of try_to_wake_up(). */ - if (p->state == TASK_WAKING) - goto fail; /* Affinity changed (again). */ if (!cpumask_test_cpu(dest_cpu, &p->cpus_allowed)) goto fail; -- 2.39.5