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From: "Paul E. McKenney" <paulmck@kernel.org>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
	mingo@kernel.org, jiangshanlai@gmail.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
	Neeraj Upadhyay <neeraju@codeaurora.org>,
	"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH rcu 13/14] rcu: Fix existing exp request check in sync_sched_exp_online_cleanup()
Date: Wed, 15 Sep 2021 16:33:42 -0700	[thread overview]
Message-ID: <20210915233343.3906738-13-paulmck@kernel.org> (raw)
In-Reply-To: <20210915233305.GA3906641@paulmck-ThinkPad-P17-Gen-1>

From: Neeraj Upadhyay <neeraju@codeaurora.org>

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>
---
 kernel/rcu/tree_exp.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index d9e4f8eb9ae2..f3947c49eee7 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -759,7 +759,7 @@ 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;
 	}
-- 
2.31.1.189.g2e36527f23


  parent reply	other threads:[~2021-09-15 23:33 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-15 23:33 [PATCH rcu 0/14] Miscellaneous fixes for v5.16 Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 01/14] rcu: Mark accesses to rcu_state.n_force_qs Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 02/14] rcu-nocb: Fix a couple of tree_nocb code-style nits Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 03/14] rcu: Eliminate rcu_implicit_dynticks_qs() local variable rnhqp Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 04/14] rcu: Eliminate rcu_implicit_dynticks_qs() local variable ruqp Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 05/14] doc: Add another stall-warning root cause in stallwarn.rst Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 06/14] rcu: Fix undefined Kconfig macros Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 07/14] rcu: Comment rcu_gp_init() code waiting for CPU-hotplug operations Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 08/14] rcu: Move rcu_dynticks_eqs_online() to rcu_cpu_starting() Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 09/14] rcu: Simplify rcu_report_dead() call to rcu_report_exp_rdp() Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 10/14] rcu: Make rcutree_dying_cpu() use its "cpu" parameter Paul E. McKenney
2021-09-16  7:28   ` Peter Zijlstra
2021-09-15 23:33 ` [PATCH rcu 11/14] rcu: Make rcu_normal_after_boot writable again Paul E. McKenney
2021-09-16  7:30   ` Peter Zijlstra
2021-09-16 13:57     ` Paul E. McKenney
2021-09-16 14:27       ` Peter Zijlstra
2021-09-16 16:53         ` Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 12/14] rcu: Make rcu update module parameters world-readable Paul E. McKenney
2021-09-15 23:33 ` Paul E. McKenney [this message]
2021-09-15 23:33 ` [PATCH rcu 14/14] rcu: Avoid unneeded function call in rcu_read_unlock() Paul E. McKenney

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