Commit 651bc1a4 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

Merge branch 'rcu/urgent' of... 

Merge branch 'rcu/urgent' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

 into core/urgent

Pull an RCU fix from Paul E. McKenney:

 "This series contains a single commit fixing an initialization bug
  reported by Amit Shah and fixed by Pranith Kumar (and tested by Amit).
  This bug results in a boot-time hang in callback-offloaded configurations
  where callbacks were posted before the offloading ('rcuo') kthreads
  were created."

Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parents 69e273c0 11ed7f93

kernel/rcu/tree.h

+1 −1
Original line number Diff line number Diff line
@@ -358,7 +358,7 @@ struct rcu_data { 
	struct rcu_head **nocb_gp_tail;

	long nocb_gp_count;

	long nocb_gp_count_lazy;

	bool nocb_leader_wake;		/* Is the nocb leader thread awake? */

	bool nocb_leader_sleep;		/* Is the nocb leader thread asleep? */

	struct rcu_data *nocb_next_follower;

					/* Next follower in wakeup chain. */

kernel/rcu/tree_plugin.h

+11 −11
Original line number Diff line number Diff line
@@ -2074,9 +2074,9 @@ static void wake_nocb_leader(struct rcu_data *rdp, bool force) 


	if (!ACCESS_ONCE(rdp_leader->nocb_kthread))

		return;

	if (!ACCESS_ONCE(rdp_leader->nocb_leader_wake) || force) {

	if (ACCESS_ONCE(rdp_leader->nocb_leader_sleep) || force) {

		/* Prior xchg orders against prior callback enqueue. */

		ACCESS_ONCE(rdp_leader->nocb_leader_wake) = true;

		ACCESS_ONCE(rdp_leader->nocb_leader_sleep) = false;

		wake_up(&rdp_leader->nocb_wq);

	}

}
@@ -2253,7 +2253,7 @@ wait_again: 
	if (!rcu_nocb_poll) {

		trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep");

		wait_event_interruptible(my_rdp->nocb_wq,

					 ACCESS_ONCE(my_rdp->nocb_leader_wake));

				!ACCESS_ONCE(my_rdp->nocb_leader_sleep));

		/* Memory barrier handled by smp_mb() calls below and repoll. */

	} else if (firsttime) {

		firsttime = false; /* Don't drown trace log with "Poll"! */
@@ -2292,12 +2292,12 @@ wait_again: 
		schedule_timeout_interruptible(1);



		/* Rescan in case we were a victim of memory ordering. */

		my_rdp->nocb_leader_wake = false;

		smp_mb();  /* Ensure _wake false before scan. */

		my_rdp->nocb_leader_sleep = true;

		smp_mb();  /* Ensure _sleep true before scan. */

		for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower)

			if (ACCESS_ONCE(rdp->nocb_head)) {

				/* Found CB, so short-circuit next wait. */

				my_rdp->nocb_leader_wake = true;

				my_rdp->nocb_leader_sleep = false;

				break;

			}

		goto wait_again;
@@ -2307,17 +2307,17 @@ wait_again: 
	rcu_nocb_wait_gp(my_rdp);



	/*

	 * We left ->nocb_leader_wake set to reduce cache thrashing.

	 * We clear it now, but recheck for new callbacks while

	 * We left ->nocb_leader_sleep unset to reduce cache thrashing.

	 * We set it now, but recheck for new callbacks while

	 * traversing our follower list.

	 */

	my_rdp->nocb_leader_wake = false;

	smp_mb(); /* Ensure _wake false before scan of ->nocb_head. */

	my_rdp->nocb_leader_sleep = true;

	smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */



	/* Each pass through the following loop wakes a follower, if needed. */

	for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {

		if (ACCESS_ONCE(rdp->nocb_head))

			my_rdp->nocb_leader_wake = true; /* No need to wait. */

			my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/

		if (!rdp->nocb_gp_head)

			continue; /* No CBs, so no need to wake follower. */

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