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 51E5322489D; Mon, 13 Jan 2025 18:36:33 +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=1736793393; cv=none; b=NkOFxiWPxj3rniNm3dQUZHz8HENbRU4QFam9KDyTPpnobvptFru4JVd2B14X379n4ZSzIFxy1/6Ko2jFdtR59HKcAbt5uZjO+UigXMTw6dO8IDwqv3bgz/JdACrIuPnGq9nf6rQb2M36G83UD1iAL/dIpyUqf6AAxnU3FbRA9ak= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736793393; c=relaxed/simple; bh=HbtvBeIcZy2P32mTLCcMuGA1L+t+DPjp5Ry6smyZ6KQ=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=iu2y8RWCqInYUwlOrN+46ntmTgfogbPkh/1dQUcYyk0wtePAyQwDKvMZB6OXkh4p7c9g0u6YwPNFssvREV34PtIPoas+A8Jg30EmKyEf0rBDp1JP1obyNw87NS6HO1jFZ0Bx9oYPXaIatVVDPBqImfsM8AqJs8MscTTVVmlxMPE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fdV2axPr; 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="fdV2axPr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 34DBAC4CED6; Mon, 13 Jan 2025 18:36:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1736793393; bh=HbtvBeIcZy2P32mTLCcMuGA1L+t+DPjp5Ry6smyZ6KQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fdV2axPrlTMzZlwNXgJjfDTwMnp1wrpT2ykuPgY3jIKymkjj30V/HChrtvgIH8cPl UjQjKy/xbMt9XE1y9I/jwFaEYeJpSIdhYGpsKjoSOaEoAmzhyi457U4oPR0WJ7GkNe ftoXRkrtia1ZwTOxy6LqqtkM8C+qSGjnR0FU+N2+5bIC9fR+fSW/dr3xo0pIIb85UO zBnseMAPcpqJhUb78+Jp5dpUj2QXN6TrxueYobHaEabGerywgc2EEk5tuxr48YKbZH txhuxU+lvdnQqKwhK0dtfH4QA4qrCoMXfw7mpk80CAI0mF0/68+YlHvWaJ9vR+8Ek2 J9QqMPpfELu3Q== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Oleg Nesterov , Christian Brauner , Sasha Levin , jack@suse.cz, ak@linux.intel.com, kees@kernel.org, arnd@arndb.de Subject: [PATCH AUTOSEL 5.10 5/5] poll_wait: add mb() to fix theoretical race between waitqueue_active() and .poll() Date: Mon, 13 Jan 2025 13:36:19 -0500 Message-Id: <20250113183619.1784510-5-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250113183619.1784510-1-sashal@kernel.org> References: <20250113183619.1784510-1-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 5.10.233 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 7e0fdcf905d2..a4af5e14dffe 100644 --- a/include/linux/poll.h +++ b/include/linux/poll.h @@ -43,8 +43,16 @@ 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