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 0DE06221FAA; Mon, 2 Jun 2025 14:17:50 +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=1748873870; cv=none; b=HW+kRZczoB3byYhw8E1CeVs8B606wPnC5IVL9v3bNvoqZoKZPUbxci27I3Wl3y81j0yFZ2aNIh9G5f2/RKT62nw4rkJcO63oUjHS/Njv/L9Jk0XeornaL1tOn7XV3QRiHny5Rz9pmSzlAD7DZOZZRw2C7Vhne1Tnl/Vy6HYAJDo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748873870; c=relaxed/simple; bh=qaVQJsmjZ+5UNhzk2W9a+pEKBfERneO2+ZtdIsIBAWw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=VU87iqvCf2ZVJIbvH/S40319G3VfjF30rcE1BWNafwy9JNJWHcT25iYGtpl9EWNFvQ5XeuQ15WLha1+zdudBVXuxy9b/NfcyNsh+/cRadh22EPvEa/ITcZRIKBcw3QsD9J4vSYQabZf+1yQsUPK3BTy0oY7VpPAAHYJ4pteVRuE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Aj1ZtdQ1; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Aj1ZtdQ1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 866D5C4CEF0; Mon, 2 Jun 2025 14:17:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1748873869; bh=qaVQJsmjZ+5UNhzk2W9a+pEKBfERneO2+ZtdIsIBAWw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Aj1ZtdQ1mO6Z2mDWBgLyU6KJ+dfJqL8Los0GZDLPUAelepytYQ/by7XnX2+NEjkuM WHW+3480hqce8EyIz2r0XZt1W16sFbfU/2k4cvrIMC0CfWNh8BuABrCTx6jsIU8jjX QHZYk6m0atll60WlksikXijnu+QP7I0uVF7OTsM4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Frederic Weisbecker , Ankur Arora , "Paul E. McKenney" , Boqun Feng , Sasha Levin Subject: [PATCH 6.6 281/444] rcu: handle unstable rdp in rcu_read_unlock_strict() Date: Mon, 2 Jun 2025 15:45:45 +0200 Message-ID: <20250602134352.359452478@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250602134340.906731340@linuxfoundation.org> References: <20250602134340.906731340@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ 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