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Message-Id: <20250716004538.2720239-2-paulmck@kernel.org> Date: Tue, 15 Jul 2025 17:45:38 -0700 From: "Paul E. McKenney" <paulmck@...nel.org> To: rcu@...r.kernel.org Cc: linux-kernel@...r.kernel.org, kernel-team@...a.com, rostedt@...dmis.org, "Paul E. McKenney" <paulmck@...nel.org> Subject: [PATCH RFC 2/2] doc: Add RCU guards to checklist.rst Also note that RCU guards can be easier to use. Signed-off-by: Paul E. McKenney <paulmck@...nel.org> --- Documentation/RCU/checklist.rst | 27 +++++++++++++++++++-------- 1 file changed, 19 insertions(+), 8 deletions(-) diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst index 7de3e308f330f..c9bfb2b218e52 100644 --- a/Documentation/RCU/checklist.rst +++ b/Documentation/RCU/checklist.rst @@ -69,7 +69,13 @@ over a rather long period of time, but improvements are always welcome! 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. Acquiring a - spinlock also enters an RCU read-side critical section. + raw spinlock also enters an RCU read-side critical section. + + The guard(rcu)() and scoped_guard(rcu) primitives designate + the remainder of the current scope or the next statement, + respectively, as the RCU read-side critical section. Use of + these guards can be less error-prone than rcu_read_lock(), + rcu_read_unlock(), and friends. Please note that you *cannot* rely on code known to be built only in non-preemptible kernels. Such code can and will break, @@ -405,9 +411,11 @@ over a rather long period of time, but improvements are always welcome! 13. Unlike most flavors of RCU, it *is* permissible to block in an SRCU read-side critical section (demarked by srcu_read_lock() and srcu_read_unlock()), hence the "SRCU": "sleepable RCU". - Please note that if you don't need to sleep in read-side critical - sections, you should be using RCU rather than SRCU, because RCU - is almost always faster and easier to use than is SRCU. + As with RCU, guard(srcu)() and scoped_guard(srcu) forms are + available, and often provide greater ease of use. Please note + that if you don't need to sleep in read-side critical sections, + you should be using RCU rather than SRCU, because RCU is almost + always faster and easier to use than is SRCU. Also unlike other forms of RCU, explicit initialization and cleanup is required either at build time via DEFINE_SRCU() @@ -443,10 +451,13 @@ 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 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. + 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. As with RCU and SRCU, guard(rcu_tasks_trace)() and + scoped_guard(rcu_tasks_trace) are available, and often provide + greater ease of use. Note that rcu_assign_pointer() relates to SRCU just as it does to other forms of RCU, but instead of rcu_dereference() you should -- 2.40.1
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