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 D95FA280029; Mon, 5 May 2025 22:36:46 +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=1746484607; cv=none; b=QvpXJ/VmVlTlI3ucO01ndGJ9xlPBSMaU/g06TP2gI1juFnJb0yIsn5QCv9npinOWgd4XoHdsXxeFbcEHndRt9sHK5A4c8a27MSbkCnTMY/C4supsQe6g/3s90+8qqU/vt+SlWEj8op8+zOR1RYhWmLbJXt9u4z2FD/ePdKqHmhc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746484607; c=relaxed/simple; bh=OdCFYJiJsQG9/MRP4AevVrePuCpVDBT1BqNHbuSmPxw=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Wcq/07EPoLg66G4IdlXMbLM8GsbGq1rZz2ZgllvHTxDW2bBAIM0taMob56+Pix6FGSrc89pwoHIvP7xigytwzkoQpECLFpzVuh6FZDNvk+99+dwXnqiFo9gqwL2VTu0RtUmse3Ll+70AoeYqf8PhvK15B59Gf3ZxJX5ayKFe3Qg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jeODsUJv; 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="jeODsUJv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0D354C4CEF1; Mon, 5 May 2025 22:36:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746484606; bh=OdCFYJiJsQG9/MRP4AevVrePuCpVDBT1BqNHbuSmPxw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jeODsUJvLlE75+IYX5J4SlcPlIFfRhknzLyp7HTqO9W4Q5aEUi3ny5bXMXqbnJsDm WlPqnH8ceVg+L/AxZT94cNJjo2tLtYcXSWrLf3tcxO8K/EAae7qIk+15Zrsp8UzhhV i9ajLtEANSbyOvIjaXn8dB+9UbgxkGX0a2M9C//iaB/gXFDJfdHjrBc9guIZz5WZuF 02Yka5XuQQoGo8pCAhPvnvcPW/oyKNJOA+L3srn9W+t8BS9qd6gB/SkdeNI4mUql+l dKHIo++oCUIX4/3wBv0907p7SV8uL76YmyQiLQl759yHGNgLAJRV7mrBaJdrlW2z6U XqisTdCujf4AQ== 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 6.14 558/642] rcu: handle unstable rdp in rcu_read_unlock_strict() Date: Mon, 5 May 2025 18:12:54 -0400 Message-Id: <20250505221419.2672473-558-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250505221419.2672473-1-sashal@kernel.org> References: <20250505221419.2672473-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.14.5 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 bd69ddc102fbc..0844ab3288519 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -95,9 +95,9 @@ 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 4328ff3252a35..3c0bbbbb686fe 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -833,8 +833,17 @@ 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