Commit-ID: 630c7ed9ca0608912fa7c8591d05dfc8742dc9e6
Gitweb: http://git.kernel.org/tip/630c7ed9ca0608912fa7c8591d05dfc8742dc9e6
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Thu, 15 Dec 2016 15:37:47 -0800
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Mon, 23 Jan 2017 11:37:13 -0800
rcu: Don't wake rcuc/X kthreads on NOCB CPUs
Chris Friesen notice that rcuc/X kthreads were consuming CPU even on
NOCB CPUs. This makes no sense because the only purpose or these
kthreads is to invoke normal (non-offloaded) callbacks, of which there
will never be any on NOCB CPUs. This problem was due to a bug in
cpu_has_callbacks_ready_to_invoke(), which should have been checking
->nxttail[RCU_NEXT_TAIL] for NULL, but which was instead (incorrectly)
checking ->nxttail[RCU_DONE_TAIL]. Because ->nxttail[RCU_DONE_TAIL] is
never NULL, the only effect is to cause the rcuc/X kthread to execute
when it should not do so.
This commit therefore checks ->nxttail[RCU_NEXT_TAIL], which is NULL
for NOCB CPUs.
Reported-by: Chris Friesen <chris.friesen@xxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
---
kernel/rcu/tree.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index d7b63b8..be23012 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -611,7 +611,7 @@ static int
cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
{
return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
- rdp->nxttail[RCU_DONE_TAIL] != NULL;
+ rdp->nxttail[RCU_NEXT_TAIL] != NULL;
}
/*
--
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