From: 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,
Frederic Weisbecker <frederic@kernel.org>,
Neeraj Upadhyay <neeraju@codeaurora.org>,
Boqun Feng <boqun.feng@gmail.com>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 03/12] rcu/nocb: Comment the reason behind BH disablement on batch processing
Date: Wed, 3 Mar 2021 16:23:02 -0800 [thread overview]
Message-ID: <20210304002311.23655-3-paulmck@kernel.org> (raw)
In-Reply-To: <20210304002225.GA23492@paulmck-ThinkPad-P72>
From: Frederic Weisbecker <frederic@kernel.org>
This commit explains why softirqs need to be disabled while invoking
callbacks, even when callback processing has been offloaded. After
all, invoking callbacks concurrently is one thing, but concurrently
invoking the same callback is quite another.
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>
Signed-off-by: Paul E. McKenney <paulmck@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 cd513ea..013142d 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);
+ /*
+ * Disable BH to provide the expected environment. Also, when
+ * transitioning to/from NOCB mode, a self-requeuing callback might
+ * be invoked from softirq. A short grace period could cause both
+ * instances of this callback would execute concurrently.
+ */
local_bh_disable();
rcu_do_batch(rdp);
local_bh_enable();
--
2.9.5
next prev parent reply other threads:[~2021-03-04 1:09 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-04 0:22 [PATCH tip/core/rcu 0/12] NOCB updates for v5.13 Paul E. McKenney
2021-03-04 0:23 ` [PATCH tip/core/rcu 01/12] rcu/nocb: Detect unsafe checks for offloaded rdp paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 02/12] timer: Report ignored local enqueue in nohz mode paulmck
2021-03-04 11:58 ` Rafael J. Wysocki
2021-03-04 20:06 ` Paul E. McKenney
2021-03-04 0:23 ` paulmck [this message]
2021-03-04 0:23 ` [PATCH tip/core/rcu 04/12] rcu/nocb: Forbid NOCB toggling on offline CPUs paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 05/12] rcu/nocb: Avoid confusing double write of rdp->nocb_cb_sleep paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 06/12] rcu/nocb: Only (re-)initialize segcblist when needed on CPU up paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 07/12] rcu/nocb: Rename nocb_gp_update_state to nocb_gp_update_state_deoffloading paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 08/12] rcu: Make nocb_nobypass_lim_per_jiffy static paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 09/12] rcu/nocb: Fix missed nocb_timer requeue paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 10/12] rcu/nocb: Disable bypass when CPU isn't completely offloaded paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 11/12] rcu/nocb: Remove stale comment above rcu_segcblist_offload() paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 12/12] rcu/nocb: Move trace_rcu_nocb_wake() calls outside nocb_lock when possible paulmck
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