From patchwork Thu Jan 16 20:02:33 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 13942183 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 D33D81DE894; Thu, 16 Jan 2025 20:02:41 +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=1737057761; cv=none; b=oB3SkmEEm+q1fx3b4WyTMBLizy0NyKO9VBDkoE8Y8rbXKSaKZ5RLWJfFu+K1OCi1+/Tas2AxQCc4s/tWVs3C5yWczBNL9bX99yRd+h70cisRmrg1dT2Q0lafWfLBMOkoGJod3Cosul+UfMveFbjOhcrhWqLTU5yk8zNdjUnNJDQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737057761; c=relaxed/simple; bh=lafpHyVaSYlRTcQ8LIw7WT/QIW65DigJmxVxCRz15TA=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=T/b12YEZFTmpb2TW06jRn+uQSwk1SPgSrD7iSTleabqlmJZyZ7KE8tSkKHDKyHbTUUk8ua4gyJIR+J26fpxuHyu4SYNAX+zm1HseJcBIJhcVIl0Fggq0GZIK+HNKb7YA5H+BAv8rzN5mW0f6nkfNZcsB3SKAOhum+UFqx0iW7c0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GC8028aJ; 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="GC8028aJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 726CFC4CED6; Thu, 16 Jan 2025 20:02:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1737057761; bh=lafpHyVaSYlRTcQ8LIw7WT/QIW65DigJmxVxCRz15TA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GC8028aJN+2xagjw79rkzXVZmwPzhF0F8aF7sEPSO1IamPMXS5BEvFn3NmjUTU+YR rwZUlFxuDaS6fVUwoazh9ft1l0NtrIdl5+CjZsyV4W5pZNGLy+IaMNFxqm15WohSH3 svgJnOwaRFqIWrvPN0IN1CD1c/xreBBhSv7x3lTXWYOaL2Yuu53y515TJdnRqGgwqB UuIkPk9h3KPVUGncu/vgwoEjt9JtjKMoUah4rxQY8kPKTdlj2YexH50lYphRDZRXu8 Nqn4a61iacwkwtYFGufPeljqski1b3ObA1OSTDJ2eheyL6U/lF3b9Ky8A1MHoiS4xR acmjXhyLJZfHQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 298B9CE0EDF; Thu, 16 Jan 2025 12:02:41 -0800 (PST) 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 rcu 1/7] doc: Add broken-timing possibility to stallwarn.rst Date: Thu, 16 Jan 2025 12:02:33 -0800 Message-Id: <20250116200239.3782374-1-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Currently, stallwarn.rst does not mention the fact that timer bugs can result in false-positive RCU CPU stall warnings. This commit therefore adds this to the list. Signed-off-by: Paul E. McKenney --- Documentation/RCU/stallwarn.rst | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst index 30080ff6f4062..d1ccd6039a8c3 100644 --- a/Documentation/RCU/stallwarn.rst +++ b/Documentation/RCU/stallwarn.rst @@ -96,6 +96,13 @@ warnings: the ``rcu_.*timer wakeup didn't happen for`` console-log message, which will include additional debugging information. +- A timer issue causes time to appear to jump forward, so that RCU + believes that the RCU CPU stall-warning timeout has been exceeded + when in fact much less time has passed. This could be due to + timer hardware bugs, timer driver bugs, or even corruption of + the "jiffies" global variable. These sorts of timer hardware + and driver bugs are not uncommon when testing new hardware. + - A low-level kernel issue that either fails to invoke one of the variants of rcu_eqs_enter(true), rcu_eqs_exit(true), ct_idle_enter(), ct_idle_exit(), ct_irq_enter(), or ct_irq_exit() on the one