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 2F02A278E4C; Mon, 5 May 2025 22:55:07 +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=1746485708; cv=none; b=B1fk6U/k31VDP7IoW3HQDQ7DjDBX/1+ZpI1pHHp3FzTtDqh998LlpTyNFlaPlZDo+84VEtAXNktGNulLKw/MYvvCfkjylAMFKyxyNa0L6o4CkWoU28pN+yElYtEw5erMiS55iGFLlEInTPMle3Haw6VPJuEQPQM/Gtce97ydwgY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746485708; c=relaxed/simple; bh=D0PUAo9KDwCLT06OfXozEdjyc4p5w+SxoL0+1i9fV8U=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=mXCEV/komyKqIwkF4wJ/tFILcWQxkS0Bua9HLvDNpKACENtdXb3w/7guRwxA4Nlo/3pDZTPP6bTNzIhuUdZ9pM/FyiFJGjzpN6/bvOe1Zpsn0XhhpgqdD6qwLUeABkMz7E4L+3lOKSRKxK+wMQD9iXIbXmX4TA7k9JUIr49rqy4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DSN2Ml/w; 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="DSN2Ml/w" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C1428C4CEE4; Mon, 5 May 2025 22:55:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746485707; bh=D0PUAo9KDwCLT06OfXozEdjyc4p5w+SxoL0+1i9fV8U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DSN2Ml/wMQ0kyvqEU7hZln0KiuPEheHmGY8Fv1T4DAo0h4AKOWlJe64NpQJJn/FKX Z71Lr6NYlNgBeY4cG/eFRrhVlF4rRXwFopOfufowOBtUdW1l2VW7zkZ7KOqLjf2yyP gbdbRKRdaoWJb3NbxEalyVGP3Fxvoa9cnYzOpZD/v546ADzDL5CH0RgZg3v7QnlPS2 naG+2/OyxZ9RewzHMbHQpovKtsXDfr/v4G5l95kzABDO7Kaxu5ilH0Rs/yTNNLfETY KiRt7CEHGQb3BXK8sF/jl06D3dARaaeWAdQMqMlnczhFzwA5k8K6dOHsGQwhcUj8lS xzFky99r30sHA== 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 6.12 435/486] rcu: handle unstable rdp in rcu_read_unlock_strict() Date: Mon, 5 May 2025 18:38:31 -0400 Message-Id: <20250505223922.2682012-435-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250505223922.2682012-1-sashal@kernel.org> References: <20250505223922.2682012-1-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 6.12.26 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 75ba4d5788c0f..304e3405e6ec7 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -832,8 +832,17 @@ 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