From: Frederic Weisbecker <frederic@kernel.org>
To: "Paul E . McKenney" <paulmck@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
Boqun Feng <boqun.feng@gmail.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Neeraj Upadhyay <neeraju@codeaurora.org>,
Josh Triplett <josh@joshtriplett.org>,
Stable <stable@vger.kernel.org>,
Joel Fernandes <joel@joelfernandes.org>
Subject: [PATCH 02/16] rcu/nocb: Comment the reason behind BH disablement on batch processing
Date: Thu, 28 Jan 2021 18:12:08 +0100 [thread overview]
Message-ID: <20210128171222.131380-3-frederic@kernel.org> (raw)
In-Reply-To: <20210128171222.131380-1-frederic@kernel.org>
Explain why we need to disable softirqs while processing callbacks in
an offline fashion. The subtle reason doesn't want to be forgotten.
Reported-by: Boqun Feng <boqun.feng@gmail.com>
Reported-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
kernel/rcu/tree_plugin.h | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index a44f80d7661b..dcfae03eb9e9 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2235,6 +2235,12 @@ static void nocb_cb_wait(struct rcu_data *rdp)
local_irq_save(flags);
rcu_momentary_dyntick_idle();
local_irq_restore(flags);
+ /*
+ * While transitioning to/from NOCB mode, a CPU might execute the same
+ * callback concurrently if it requeues itself and the softirq interrupts
+ * the offloaded callback processing. Make sure we disable BH to prevent
+ * from that.
+ */
local_bh_disable();
rcu_do_batch(rdp);
local_bh_enable();
--
2.25.1
next prev parent reply other threads:[~2021-01-28 17:16 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-28 17:12 [PATCH 00/16] rcu/nocb updates Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 01/16] rcu/nocb: Fix potential missed nocb_timer rearm Frederic Weisbecker
[not found] ` <20210128184834.GP2743@paulmck-ThinkPad-P72>
2021-01-28 21:23 ` Frederic Weisbecker
2021-01-28 17:12 ` Frederic Weisbecker [this message]
2021-01-28 17:12 ` [PATCH 03/16] rcu/nocb: Forbid NOCB toggling on offline CPUs Frederic Weisbecker
2021-01-28 19:52 ` Paul E. McKenney
2021-01-28 17:12 ` [PATCH 04/16] rcu/nocb: Only (re-)initialize segcblist when needed on CPU up Frederic Weisbecker
[not found] ` <20210128191228.GQ2743@paulmck-ThinkPad-P72>
2021-01-28 21:34 ` Frederic Weisbecker
2021-01-28 21:45 ` Paul E. McKenney
2021-01-29 0:26 ` Paul E. McKenney
2021-01-28 17:12 ` [PATCH 05/16] rcu/nocb: Disable bypass when CPU isn't completely offloaded Frederic Weisbecker
2021-01-28 21:31 ` Paul E. McKenney
2021-01-28 22:25 ` Frederic Weisbecker
2021-01-29 0:19 ` Paul E. McKenney
2021-01-28 17:12 ` [PATCH 06/16] rcu/nocb: Avoid confusing double write of rdp->nocb_cb_sleep Frederic Weisbecker
2021-01-28 21:42 ` Paul E. McKenney
2021-01-28 17:12 ` [PATCH 07/16] rcu/nocb: Rename nocb_gp_update_state to nocb_gp_update_state_deoffloading Frederic Weisbecker
2021-01-29 0:49 ` Paul E. McKenney
2021-01-28 17:12 ` [PATCH 08/16] rcu/nocb: Move trace_rcu_nocb_wake() calls outside nocb_lock when possible Frederic Weisbecker
2021-01-29 0:51 ` Paul E. McKenney
2021-01-28 17:12 ` [PATCH 09/16] rcu/nocb: Merge nocb_timer to the rdp leader Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 10/16] rcu/nocb: Directly call __wake_nocb_gp() from bypass timer Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 11/16] rcu/nocb: Allow de-offloading rdp leader Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 12/16] rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 13/16] rcu/nocb: Delete bypass_timer " Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 14/16] rcu/nocb: Only cancel nocb timer if not polling Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 15/16] rcu/nocb: Prepare for finegrained deferred wakeup Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 16/16] rcu/nocb: Unify timers Frederic Weisbecker
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