From nobody Tue Oct 7 03:50:40 2025 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A1D0D4315C; Wed, 16 Jul 2025 00:45:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752626740; cv=none; b=WMfmnsAn0wXL4YxoX0BlLwi+/zzRVLwX7RtVH03vHz8idaN2vypH4NAuIUSLbjs7LxfEIhTZYQRHcCBXZ/gpt4gQCz3oMCVU1U6UgYbPdgvAQoBKDvReI8uhCY/bEgY7Ldb1TpKJVWpdgj2bFV6ATEBWqOJlia+6jATGuerEkAE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752626740; c=relaxed/simple; bh=4hZa1H+8tV2PdJc9DZTrt0zGwOLM6dKOexYzKnOiVxU=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=bG6TbNaxNyqwjjqnZ8j+hCkcskzQpMJ5jAppNizloUS4ghi2vUERWOOBa0uqkGYoWfVevRjSKxnmYyxYIcG5cftfZGRJmNW3ZszHtT+8HzDW2SOyAWUu+0NsiS6O038Zh5sIRyxtYJoyCpV8aSJ4EY6gdxYqyy1Fagqyh7WoisY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=g7S+46ac; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="g7S+46ac" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 49EE5C4CEE3; Wed, 16 Jul 2025 00:45:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1752626740; bh=4hZa1H+8tV2PdJc9DZTrt0zGwOLM6dKOexYzKnOiVxU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=g7S+46accG5J4oZExQ55dMY46B24ULY6v98TbaecdtWMFS7S2pSv3+JGc6f8LghWL JyRcQBuoW1qqXyNE4dcK8IE4MaRj6m2WmuXzgIpn41zKh9HmGMlWLID/tWu6XIfaUQ HquXw0WVa2F+vsQERQSHAYlVP0iA3BoTCyBIvmqK494jR8JqDOIZobDVtrTM8qD0kp e3xC4MKyuH70C7zLd323JjyxCUoVytAb75nAgC2gp91ouLY9BTlCKQ6sACXgVvo7cs nhmCDzhcsin7FZGG3bX0CGZvm/IcNidDQOi9nfoHL7uGkyxIdYzJLqjf73tL+Uy0VX +Gg2PRwBGHPiw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id F37FBCE0ADE; Tue, 15 Jul 2025 17:45:39 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, "Paul E. McKenney" Subject: [PATCH RFC 2/2] doc: Add RCU guards to checklist.rst Date: Tue, 15 Jul 2025 17:45:38 -0700 Message-Id: <20250716004538.2720239-2-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <70015517-57ab-4d07-9792-3ab1beced9e4@paulmck-laptop> References: <70015517-57ab-4d07-9792-3ab1beced9e4@paulmck-laptop> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Also note that RCU guards can be easier to use. Signed-off-by: Paul E. McKenney --- 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. =20 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 ar= e 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. =20 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 a= re always welcome! real-time workloads than is synchronize_rcu_expedited(). =20 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. =20 Note that rcu_assign_pointer() relates to SRCU just as it does to other forms of RCU, but instead of rcu_dereference() you should --=20 2.40.1