rcu: Fix existing exp request check in sync_sched_exp_online_cleanup()

BugLink: https://bugs.launchpad.net/bugs/1953387
[ 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@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index df90d4d7ad2e249418e4b9189dc6351de2e2aaef..4c4d7683a4e5ba1f3a8e54590abbf0a863885b7c 100644 (file)
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -738,7 +738,7 @@ 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;
        }