This is a note to let you know that I've just added the patch titled
rcu: Fix existing exp request check in sync_sched_exp_online_cleanup()
to the 5.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
rcu-fix-existing-exp-request-check-in-sync_sched_exp.patch
and it can be found in the queue-5.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 0a2a2ee7661be8b6151d6b617deb41624fd5789a
Author: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
Date: Wed Aug 18 13:34:00 2021 +0530
rcu: Fix existing exp request check in sync_sched_exp_online_cleanup()
[ Upstream commit f0b2b2df5423fb369ac762c77900bc7765496d58 ]
The sync_sched_exp_online_cleanup() checks to see if RCU needs
an expedited quiescent state from the incoming CPU, sending it
an IPI if so. Before sending IPI, it checks whether expedited
qs need has been already requested for the incoming CPU, by
checking rcu_data.cpu_no_qs.b.exp for the current cpu, on which
sync_sched_exp_online_cleanup() is running. This works for the
case where incoming CPU is same as self. However, for the case
where incoming CPU is different from self, expedited request
won't get marked, which can potentially delay reporting of
expedited quiescent state for the incoming CPU.
Fixes: e015a3411220 ("rcu: Avoid self-IPI in sync_sched_exp_online_cleanup()")
Signed-off-by: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 2796084ef85a5..454b516ea566e 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -760,7 +760,7 @@ static void sync_sched_exp_online_cleanup(int cpu)
my_cpu = get_cpu();
/* Quiescent state either not needed or already requested, leave. */
if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
- __this_cpu_read(rcu_data.cpu_no_qs.b.exp)) {
+ rdp->cpu_no_qs.b.exp) {
put_cpu();
return;
}
