linux-kernel - [PATCH] rcu: Add rnp->cbovldmask check in rcutree_migrate

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Date:   Thu,  5 May 2022 23:52:36 +0800
From:   Zqiang <qiang1.zhang@...el.com>
To:     paulmck@...nel.org, frederic@...nel.org
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] rcu: Add rnp->cbovldmask check in rcutree_migrate_callbacks()

Currently, the rnp's cbovlmask is set in call_rcu(). when CPU going
offline, the outgoing CPU's callbacks is migrated to target CPU, the
number of callbacks on the my_rdp may be overloaded, if overload and
there is no call_rcu() call on target CPU for a long time, the rnp's
cbovldmask is not set in time. in order to fix this situation, add
check_cb_ovld_locked() in rcutree_migrate_callbacks() to help CPU more
quickly reach quiescent states.

Signed-off-by: Zqiang <qiang1.zhang@...el.com>
---
 kernel/rcu/tree.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 9dc4c4e82db6..bcc5876c9753 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4577,6 +4577,7 @@ void rcutree_migrate_callbacks(int cpu)
 	needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp);
 	rcu_segcblist_disable(&rdp->cblist);
 	WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist));
+	check_cb_ovld_locked(my_rdp, my_rnp);
 	if (rcu_rdp_is_offloaded(my_rdp)) {
 		raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */
 		__call_rcu_nocb_wake(my_rdp, true, flags);
-- 
2.25.1