Author: Oleg Nesterov <email@example.com>
AuthorDate: Mon Mar 15 10:10:10 2010 +0100
Committer: Ingo Molnar <firstname.lastname@example.org>
CommitDate: Fri Apr 2 20:12:01 2010 +0200
sched: move_task_off_dead_cpu(): Take rq->lock around select_fallback_rq()
move_task_off_dead_cpu()->select_fallback_rq() reads/updates ->cpus_allowed
lockless. We can race with set_cpus_allowed() running in parallel.
Change it to take rq->lock around select_fallback_rq(). Note that it is not
trivial to move this spin_lock() into select_fallback_rq(), we must recheck
the task was not migrated after we take the lock and other callers do not
need this lock.
To avoid the races with other callers of select_fallback_rq() which rely on
TASK_WAKING, we also check p->state != TASK_WAKING and do nothing otherwise.
The owner of TASK_WAKING must update ->cpus_allowed and choose the correct
CPU anyway, and the subsequent __migrate_task() is just meaningless because
p->se.on_rq must be false.
Alternatively, we could change select_task_rq() to take rq->lock right
after it calls sched_class->select_task_rq(), but this looks a bit ugly.
Also, change it to not assume irqs are disabled and absorb __migrate_task_irq().
Signed-off-by: Oleg Nesterov <email@example.com>
Signed-off-by: Peter Zijlstra <firstname.lastname@example.org>
Signed-off-by: Ingo Molnar <email@example.com>
kernel/sched.c | 30 +++++++++++++++---------------
1 files changed, 15 insertions(+), 15 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index c0b3ebc..27774b5 100644
@@ -5448,29 +5448,29 @@ static int migration_thread(void *data)