Commit fda67514 authored by Linus Torvalds's avatar Linus Torvalds

Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fix from Ingo Molnar:
 "A try_to_wake_up() memory ordering race fix causing a busy-loop in
  ttwu()"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/core: Fix a race between try_to_wake_up() and a woken up task
parents ee319d58 135e8c92
......@@ -2016,6 +2016,28 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
success = 1; /* we're going to change ->state */
cpu = task_cpu(p);
/*
* Ensure we load p->on_rq _after_ p->state, otherwise it would
* be possible to, falsely, observe p->on_rq == 0 and get stuck
* in smp_cond_load_acquire() below.
*
* sched_ttwu_pending() try_to_wake_up()
* [S] p->on_rq = 1; [L] P->state
* UNLOCK rq->lock -----.
* \
* +--- RMB
* schedule() /
* LOCK rq->lock -----'
* UNLOCK rq->lock
*
* [task p]
* [S] p->state = UNINTERRUPTIBLE [L] p->on_rq
*
* Pairs with the UNLOCK+LOCK on rq->lock from the
* last wakeup of our task and the schedule that got our task
* current.
*/
smp_rmb();
if (p->on_rq && ttwu_remote(p, wake_flags))
goto stat;
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment