linux-kernel - [PATCH 3/8] doc: Make checklist.rst note that spinlocks are implied RCU readers

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Date: Thu, 25 Jan 2024 19:58:06 -0800
From: Boqun Feng <boqun.feng@...il.com>
To: linux-kernel@...r.kernel.org,
	rcu@...r.kernel.org,
	linux-doc@...r.kernel.org
Cc: Jonathan Corbet <corbet@....net>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.iitr10@...il.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>
Subject: [PATCH 3/8] doc: Make checklist.rst note that spinlocks are implied RCU readers

From: "Paul E. McKenney" <paulmck@...nel.org>

In kernels built with CONFIG_PREEMPT_RT=n, spinlock critical sections
are RCU readers because they disable preemption.  However, they are also
RCU readers in CONFIG_PREEMPT_RT=y because in that case the locking
primitives contain rcu_read_lock() and rcu_read_unlock().  Therefore,
upgrade checklist.rst to document this non-obvious case.

While in the area, fix a typo by changing "read-side critical" to
"read-side critical section".

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 Documentation/RCU/checklist.rst | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst
index 2d42998a89a6..98a622f77248 100644
--- a/Documentation/RCU/checklist.rst
+++ b/Documentation/RCU/checklist.rst
@@ -68,7 +68,8 @@ over a rather long period of time, but improvements are always welcome!
 	rcu_read_lock_sched(), or by the appropriate update-side lock.
 	Explicit disabling of preemption (preempt_disable(), for example)
 	can serve as rcu_read_lock_sched(), but is less readable and
-	prevents lockdep from detecting locking issues.
+	prevents lockdep from detecting locking issues.  Acquiring a
+	spinlock also enters an RCU read-side critical section.
 
 	Please note that you *cannot* rely on code known to be built
 	only in non-preemptible kernels.  Such code can and will break,
@@ -444,7 +445,7 @@ over a rather long period of time, but improvements are always welcome!
 	real-time workloads than is synchronize_rcu_expedited().
 
 	It is also permissible to sleep in RCU Tasks Trace read-side
-	critical, which are delimited by rcu_read_lock_trace() and
+	critical section, which are delimited by rcu_read_lock_trace() and
 	rcu_read_unlock_trace().  However, this is a specialized flavor
 	of RCU, and you should not use it without first checking with
 	its current users.  In most cases, you should instead use SRCU.
-- 
2.43.0