Messages in this thread Patch in this message | | | Date | Sat, 18 Sep 2010 11:57:34 -0700 | From | Greg KH <> | Subject | [010/123] sched: revert stable c6fc81a sched: Fix a race between ttwu() and migrate_task() |
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From: Mike Galbraith <efault@gmx.de>
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 <efault@gmx.de> Cc: Ingo Molnar <mingo@elte.hu> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- kernel/sched.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)
--- a/kernel/sched.c +++ b/kernel/sched.c @@ -2123,10 +2123,12 @@ migrate_task(struct task_struct *p, int /* * 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_st /* 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;
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