From c6fc81afa2d7ef2f775e48672693d8a0a8a7325d Mon Sep 17 00:00:00 2001 From: John Wright Date: Tue, 13 Apr 2010 16:55:37 -0600 Subject: [PATCH] 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: John Wright Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Greg Kroah-Hartman --- kernel/sched.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 2591562eae13..3261c1986b5b 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2116,12 +2116,10 @@ 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 - * it is sufficient to simply update the task's cpu field. + * the next wake-up will properly place the task. */ - if (!p->se.on_rq && !task_running(rq, p)) { - set_task_cpu(p, dest_cpu); + if (!p->se.on_rq && !task_running(rq, p)) return 0; - } init_completion(&req->done); req->task = p; @@ -7167,6 +7165,9 @@ 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