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: Ingo Molnar <mingo@kernel.org>

2 files changed, 12 insertions, 12 deletions

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 71e64c718f75..6a86eb7bac45 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -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. */
 
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 00dc411e9676..a7997e272564 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -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. */