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 99D821FA8C6; Mon, 13 Jan 2025 18:35:11 +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=1736793311; cv=none; b=U6PYwVY5wuIdJcH5I9ijOVgH6yCi9hiq//CvM6a2ty/wNPdJKmuqpc4M+E63diKl1zneeGJrX+lNg2KtWwXmqQqPnxsiAySYuY9BcxoGVUeIddkuiZWbgKTrAMKJLS8+kaavSNJd0/wWtEnW9wPSIzWtNTiknx5TrmkXHVloEKk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736793311; c=relaxed/simple; bh=n0Pf6qpGoYAXXTCIUxq4k5sAvt6d3JS46oA5bUdbivA=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=faY3dMs2Ht50hZvuilkpx79TNllpUYoXT3EQPqVDmLXzuylJ4/tghnoX1tLmj30skHIB+TRgJ1dKvBWKKpMAt5Efgk3ZgzOaJ5xBgEQYUa89L8/ToznjEuZNsUgC9OgEO2CRWZEfgbhur75oZJHjwba5kvfM34wo9jp6URvkJTs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=msPTIKoE; 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="msPTIKoE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 41536C4CEE2; Mon, 13 Jan 2025 18:35:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1736793311; bh=n0Pf6qpGoYAXXTCIUxq4k5sAvt6d3JS46oA5bUdbivA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=msPTIKoE/Njjr8HTPGv3mFs9NyrADg/SMUvz0urDTVb2l2ijyzCMGOckEyTdeAdPm 3+jIpGlS2hxqku++Pzdv2cUjHk1mfxVyaZWg/bplh7R4LldLEV6AoK5Bw9mPe1KJ4Q juh3A4XnXjADiLYo1sePmxpwH9AbdOjv6jx1XpHz4g4Fo1MevArVd3tPhUIgxclLTZ /hvpVDVAWPv//JToB0BNN9T66MXOEb0Yestzuf7e+sWRwzoaMYchP2Gh5dY2oT8edR XfY2RWaeLerEmCoqM89Pp344mWCLOfvqQbvjhqIjSzVoA0uOJ+vfJOEtszeh3ssb4v NoPchxvzfuQBw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Oleg Nesterov , Christian Brauner , Sasha Levin , arnd@arndb.de, kees@kernel.org, ak@linux.intel.com Subject: [PATCH AUTOSEL 6.12 20/20] poll_wait: add mb() to fix theoretical race between waitqueue_active() and .poll() Date: Mon, 13 Jan 2025 13:34:25 -0500 Message-Id: <20250113183425.1783715-20-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250113183425.1783715-1-sashal@kernel.org> References: <20250113183425.1783715-1-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 6.12.9 Content-Transfer-Encoding: 8bit From: Oleg Nesterov [ Upstream commit cacd9ae4bf801ff4125d8961bb9a3ba955e51680 ] As the comment above waitqueue_active() explains, it can only be used if both waker and waiter have mb()'s that pair with each other. However __pollwait() is broken in this respect. This is not pipe-specific, but let's look at pipe_poll() for example: poll_wait(...); // -> __pollwait() -> add_wait_queue() LOAD(pipe->head); LOAD(pipe->head); In theory these LOAD()'s can leak into the critical section inside add_wait_queue() and can happen before list_add(entry, wq_head), in this case pipe_poll() can race with wakeup_pipe_readers/writers which do smp_mb(); if (waitqueue_active(wq_head)) wake_up_interruptible(wq_head); There are more __pollwait()-like functions (grep init_poll_funcptr), and it seems that at least ep_ptable_queue_proc() has the same problem, so the patch adds smp_mb() into poll_wait(). Link: https://lore.kernel.org/all/20250102163320.GA17691@redhat.com/ Signed-off-by: Oleg Nesterov Link: https://lore.kernel.org/r/20250107162717.GA18922@redhat.com Signed-off-by: Christian Brauner Signed-off-by: Sasha Levin --- include/linux/poll.h | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/include/linux/poll.h b/include/linux/poll.h index d1ea4f3714a8..fc641b50f129 100644 --- a/include/linux/poll.h +++ b/include/linux/poll.h @@ -41,8 +41,16 @@ typedef struct poll_table_struct { static inline void poll_wait(struct file * filp, wait_queue_head_t * wait_address, poll_table *p) { - if (p && p->_qproc && wait_address) + if (p && p->_qproc && wait_address) { p->_qproc(filp, wait_address, p); + /* + * This memory barrier is paired in the wq_has_sleeper(). + * See the comment above prepare_to_wait(), we need to + * ensure that subsequent tests in this thread can't be + * reordered with __add_wait_queue() in _qproc() paths. + */ + smp_mb(); + } } /* -- 2.39.5