Commit-ID: 8ba9153b2c3ab733d64e22adb57820ccb6afc496
Gitweb: http://git.kernel.org/tip/8ba9153b2c3ab733d64e22adb57820ccb6afc496
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Tue, 29 Sep 2015 07:55:41 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Fri, 4 Dec 2015 12:27:30 -0800
rcu: Remove lock-acquisition loop from rcu_read_unlock_special()
Several releases have come and gone without the warning triggering,
so remove the lock-acquisition loop. Retain the WARN_ON_ONCE()
out of sheer paranoia.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/rcu/tree_plugin.h | 18 ++++++------------
1 file changed, 6 insertions(+), 12 deletions(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 57ba873..ae4ce2b 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -449,19 +449,13 @@ void rcu_read_unlock_special(struct task_struct *t)
/*
* Remove this task from the list it blocked on. The task
- * now remains queued on the rcu_node corresponding to
- * the CPU it first blocked on, so the first attempt to
- * acquire the task's rcu_node's ->lock will succeed.
- * Keep the loop and add a WARN_ON() out of sheer paranoia.
+ * now remains queued on the rcu_node corresponding to the
+ * CPU it first blocked on, so there is no longer any need
+ * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
*/
- for (;;) {
- rnp = t->rcu_blocked_node;
- raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
- if (rnp == t->rcu_blocked_node)
- break;
- WARN_ON_ONCE(1);
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
- }
+ rnp = t->rcu_blocked_node;
+ raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
+ WARN_ON_ONCE(rnp != t->rcu_blocked_node);
empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
empty_exp = sync_rcu_preempt_exp_done(rnp);
smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
--
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