From mboxrd@z Thu Jan 1 00:00:00 1970 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 7469E22DA0E; Mon, 5 May 2025 23:05:31 +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=1746486332; cv=none; b=kUbRYf9RbVhog4yheNZVo0UM5M8KKG02cX0K4Fc0XM3vNn+iJqqInJ16h8XLTxtCkBcjfNzy67E9zwPxDF60wIM8iQRr9BnkzKBJ8tW2Dr9zb7dxvh/W6uU3rXadXkf31DLxca4zVc2WCsydEm5vkp7fwIzaxLk2p76FmLTecvo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746486332; c=relaxed/simple; bh=bnAqG9BCRn/8cTflVlED5Sms4sEVJMtDnAj0tO6NpOA=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=cIUriJ6vFXTWMo1ElaqmF4s8xDY90ZhsE0c1O6/Om0reVDgMtTIxQcSaA2EoM/ZtsmJI3hpRJVUaIYyNK1bmxEqFOne1CikcXb9oozShXu3jNJG/55c24p9X178ngCpxHQXJu3OwtYKmomOInePZtFcZRdwSugPagdq6XurvMC0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=aT1mSqki; 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="aT1mSqki" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9AB9BC4CEED; Mon, 5 May 2025 23:05:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746486330; bh=bnAqG9BCRn/8cTflVlED5Sms4sEVJMtDnAj0tO6NpOA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=aT1mSqkiF+bh/WBUaYWwTWVMPWM0MvTVNw9IGNRaWa32OfUPIq/l6EqUo8bcQBd4d 0GKioZ7UxF/B+7Ti3IMkEs6+RIHqCMN5ucOO/fca6sZHRg1xg46+dO1BYx7E59esFR CmoY/lW5UmaZtpgvbcED0tBdXSs1IefK/bwgZDLA8pOq95MMwFM9g26tu9uc5Heur0 uZpQ/5GHwT27wPBEmJaUJqfqJfrVVpwbuKNXmRjH1scNQIgjnFsRzfK8DVBXP1rPPl EYmHwFOYseh5vbr+/YLfiIRbjmu8thwR4Hhf1Qp4xc+Rx/EBJO7Lye60h1hB+XOU5s ZvGFVI4CXYltQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Ankur Arora , Frederic Weisbecker , "Paul E . McKenney" , Boqun Feng , Sasha Levin , neeraj.upadhyay@kernel.org, joel@joelfernandes.org, josh@joshtriplett.org, urezki@gmail.com, rcu@vger.kernel.org Subject: [PATCH AUTOSEL 6.6 263/294] rcu: handle unstable rdp in rcu_read_unlock_strict() Date: Mon, 5 May 2025 18:56:03 -0400 Message-Id: <20250505225634.2688578-263-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250505225634.2688578-1-sashal@kernel.org> References: <20250505225634.2688578-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.6.89 Content-Transfer-Encoding: 8bit From: Ankur Arora [ Upstream commit fcf0e25ad4c8d14d2faab4d9a17040f31efce205 ] rcu_read_unlock_strict() can be called with preemption enabled which can make for an unstable rdp and a racy norm value. Fix this by dropping the preempt-count in __rcu_read_unlock() after the call to rcu_read_unlock_strict(), adjusting the preempt-count check appropriately. Suggested-by: Frederic Weisbecker Signed-off-by: Ankur Arora Reviewed-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney Signed-off-by: Boqun Feng Signed-off-by: Sasha Levin --- include/linux/rcupdate.h | 2 +- kernel/rcu/tree_plugin.h | 11 ++++++++++- 2 files changed, 11 insertions(+), 2 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 72da69cc5764f..27531a0b3a6e7 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -97,9 +97,9 @@ static inline void __rcu_read_lock(void) static inline void __rcu_read_unlock(void) { - preempt_enable(); if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) rcu_read_unlock_strict(); + preempt_enable(); } static inline int rcu_preempt_depth(void) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index dccfc46496393..94b715139f52d 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -821,8 +821,17 @@ void rcu_read_unlock_strict(void) { struct rcu_data *rdp; - if (irqs_disabled() || preempt_count() || !rcu_state.gp_kthread) + if (irqs_disabled() || in_atomic_preempt_off() || !rcu_state.gp_kthread) return; + + /* + * rcu_report_qs_rdp() can only be invoked with a stable rdp and + * from the local CPU. + * + * The in_atomic_preempt_off() check ensures that we come here holding + * the last preempt_count (which will get dropped once we return to + * __rcu_read_unlock(). + */ rdp = this_cpu_ptr(&rcu_data); rdp->cpu_no_qs.b.norm = false; rcu_report_qs_rdp(rdp); -- 2.39.5