From nobody Tue Nov 26 04:46:03 2024 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 61BEC1C4609; Mon, 21 Oct 2024 22:13:06 +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=1729548786; cv=none; b=hFp0IbaG0dKI91gM+N1/dmU2ki05U7mAQ5XheQ5AQAo/yw+GYpZpkDxMBjDT6H0SgtHhQ7IKv1oAPjVjYPW2kATy4/eIkGVplxMi9vt7Iz+qkmcDSxVmjkMllLl5nAeh7GJvdWEX83yOmTvqv+30AX5s3J2QAuXZwo81TUJ2KF4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729548786; c=relaxed/simple; bh=M5yWAF/R0QTARoO4jvZtiId1CKtuH6rgLGc/G5eCqss=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition; b=UiGjo/VqaK+39o48HXn8TCp5A+n8SuSarz/D+O8NeH7cgrckmEAj2nG8g42ASjiN51F693+/tFSXne0K53riNgRHqQf2sN0av1QVBhXTQGzBRnsKjhuMJ/cBieqa0RZRxEnXthmsJel0GHQ3wgzqp720VzWHK4059Pig8YA0kiU= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FYLLQSY8; 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="FYLLQSY8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D6DCCC4CEC3; Mon, 21 Oct 2024 22:13:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1729548785; bh=M5yWAF/R0QTARoO4jvZtiId1CKtuH6rgLGc/G5eCqss=; h=Date:From:To:Cc:Subject:Reply-To:From; b=FYLLQSY8+hiNT27tq1xtyrBqatmAUSWCNIWcwsInBotQo7eCmN8NCQXAtoXNHbmaS 13OuEUpib00MVT+3hTZk6KkcnqYLOZCFIREjZ4uV9MqAMZzkBySSZtNcEqaDf73v8j IYFu6f0fahr7+kLPMQXgW+kjBw3vQTGYNPHIkIz6Bz7FgwGjl+Vp76NIFuqTifj9f/ aQXogLCrhlSHvMA5QbaIVXkzt3cgSI5B9mH/kMnizQEabmPaiJRRUyLFLZSslssQDD ymM3QECz+MwYnEjeIgGbnadXaEWQo2kYuzlipUavoVdO5vHSiG6ibqTHxwalJnQa9c pW3unPS9DnLIQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 74B77CE09F6; Mon, 21 Oct 2024 15:13:05 -0700 (PDT) Date: Mon, 21 Oct 2024 15:13:05 -0700 From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, peterz@infradead.org, andrii@kernel.org Subject: [PATCH rcu] srcu: Guarantee non-negative return value from srcu_read_lock() Message-ID: <97594073-e296-4876-9d6a-1e4a4f33d857@paulmck-laptop> Reply-To: paulmck@kernel.org Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" For almost 20 years, the int return value from srcu_read_lock() has been always either zero or one. This commit therefore documents the fact that it will be non-negative. Signed-off-by: Paul E. McKenney Cc: Peter Zijlstra Cc: Andrii Nakryiko Acked-by: Peter Zijlstra (Intel) --- a/include/linux/srcu.h +++ b/include/linux/srcu.h @@ -238,13 +238,14 @@ void srcu_check_read_flavor(struct srcu_struct *ssp, = int read_flavor); * a mutex that is held elsewhere while calling synchronize_srcu() or * synchronize_srcu_expedited(). * - * The return value from srcu_read_lock() must be passed unaltered - * to the matching srcu_read_unlock(). Note that srcu_read_lock() and - * the matching srcu_read_unlock() must occur in the same context, for - * example, it is illegal to invoke srcu_read_unlock() in an irq handler - * if the matching srcu_read_lock() was invoked in process context. Or, - * for that matter to invoke srcu_read_unlock() from one task and the - * matching srcu_read_lock() from another. + * The return value from srcu_read_lock() is guaranteed to be + * non-negative. This value must be passed unaltered to the matching + * srcu_read_unlock(). Note that srcu_read_lock() and the matching + * srcu_read_unlock() must occur in the same context, for example, it is + * illegal to invoke srcu_read_unlock() in an irq handler if the matching + * srcu_read_lock() was invoked in process context. Or, for that matter to + * invoke srcu_read_unlock() from one task and the matching srcu_read_lock= () + * from another. */ static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp) {