1 files changed, 17 insertions, 23 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index f91a20c652b5..145f27fe3a1f 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1141,37 +1141,31 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
          * they can do to advance the grace period.  It is therefore
          * safe for us to drop the lock in order to mark the grace
          * period as completed in all of the rcu_node structures.
-         *
-         * But if this CPU needs another grace period, it will take
-         * care of this while initializing the next grace period.
-         * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL
-         * because the callbacks have not yet been advanced: Those
-         * callbacks are waiting on the grace period that just now
-         * completed.
          */
-        rdp = this_cpu_ptr(rsp->rda);
-        if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) {
-                raw_spin_unlock_irq(&rnp->lock);
+        raw_spin_unlock_irq(&rnp->lock);
 
-                /*
-                 * Propagate new ->completed value to rcu_node
-                 * structures so that other CPUs don't have to
-                 * wait until the start of the next grace period
-                 * to process their callbacks.
-                 */
-                rcu_for_each_node_breadth_first(rsp, rnp) {
-                        raw_spin_lock_irq(&rnp->lock);
-                        rnp->completed = rsp->gpnum;
-                        raw_spin_unlock_irq(&rnp->lock);
-                        cond_resched();
-                }
-                rnp = rcu_get_root(rsp);
+        /*
+         * Propagate new ->completed value to rcu_node structures so
+         * that other CPUs don't have to wait until the start of the next
+         * grace period to process their callbacks.  This also avoids
+         * some nasty RCU grace-period initialization races by forcing
+         * the end of the current grace period to be completely recorded in
+         * all of the rcu_node structures before the beginning of the next
+         * grace period is recorded in any of the rcu_node structures.
+         */
+        rcu_for_each_node_breadth_first(rsp, rnp) {
                 raw_spin_lock_irq(&rnp->lock);
+                rnp->completed = rsp->gpnum;
+                raw_spin_unlock_irq(&rnp->lock);
+                cond_resched();
         }
+        rnp = rcu_get_root(rsp);
+        raw_spin_lock_irq(&rnp->lock);
 
         rsp->completed = rsp->gpnum; /* Declare grace period done. */
         trace_rcu_grace_period(rsp->name, rsp->completed, "end");
         rsp->fqs_state = RCU_GP_IDLE;
+        rdp = this_cpu_ptr(rsp->rda);
         if (cpu_needs_another_gp(rsp, rdp))
                 rsp->gp_flags = 1;
         raw_spin_unlock_irq(&rnp->lock);