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Commit fda67514 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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

kernel/sched/core.c

+22 −0
Original line number Diff line number Diff line
@@ -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;