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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,
	"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH rcu 07/14] rcu: Comment rcu_gp_init() code waiting for CPU-hotplug operations
Date: Wed, 15 Sep 2021 16:33:36 -0700	[thread overview]
Message-ID: <20210915233343.3906738-7-paulmck@kernel.org> (raw)
In-Reply-To: <20210915233305.GA3906641@paulmck-ThinkPad-P17-Gen-1>

Near the beginning of rcu_gp_init() is a per-rcu_node loop that waits
for CPU-hotplug operations that might have started before the new
grace period did.  This commit adds a comment explaining that this
wait does not exclude CPU-hotplug operations.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 0bfebec94277..e6e1b9281530 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1775,6 +1775,8 @@ static noinline_for_stack bool rcu_gp_init(void)
 	 */
 	WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF);
 	rcu_for_each_leaf_node(rnp) {
+		// Wait for CPU-hotplug operations that might have
+		// started before this grace period did.
 		smp_mb(); // Pair with barriers used when updating ->ofl_seq to odd values.
 		firstseq = READ_ONCE(rnp->ofl_seq);
 		if (firstseq & 0x1)
-- 
2.31.1.189.g2e36527f23


  parent reply	other threads:[~2021-09-15 23:34 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 ` Paul E. McKenney [this message]
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 ` [PATCH rcu 13/14] rcu: Fix existing exp request check in sync_sched_exp_online_cleanup() Paul E. McKenney
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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