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 E911B213245; Mon, 13 Jan 2025 18:36:00 +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=1736793361; cv=none; b=ETiGfQi5+OP2m1RuCP4gGjCuGZdXU5yJJTw3tBzg8ZapBXugF2FYI02Jy3ttrHDCnl5k5a0+he63FRihbFRfslRmkt240gNlXf2iOeXED2s/y33Z+nyMWuPwMQKih8OO7gzI80FkFifkbNyl9ImmMZGEOA/3s85R/S5QjL2oDrs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736793361; c=relaxed/simple; bh=n0Pf6qpGoYAXXTCIUxq4k5sAvt6d3JS46oA5bUdbivA=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=KX5AReH/HNTI8Bu3ZAtPgM34oIF1ZzF2FOUYyC+kFUViHZVCjKSNYC6WmME3OKXccwQ7CgkC9CUZxCBzM65J4Mw5JrmIvZbwcjKxYyvkcUs5Ev5jKPO9PJ1WjKYgzZa20yaf7MYDMM0A6W8Jb88hXLgET93S51+IvjujmB4N+dk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Ex7SuAyt; 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="Ex7SuAyt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8AC56C4CEE1; Mon, 13 Jan 2025 18:35:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1736793360; bh=n0Pf6qpGoYAXXTCIUxq4k5sAvt6d3JS46oA5bUdbivA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Ex7SuAytyuBdp1Lg84jGqZ00SCUHg0VG6WefvNVqCjaS4a93lYnmjXZy/xjR0IesG lklkJfdUNlHLiWVrY+e4XdC+8RbeBmSNZ7t1LoNDuD8ru9llKPRm4bDumhElULN4wl 4M4cEZau1DYljkaJiInFiOXNDALht8Blj+ERHfH/HLtny+WvbEJX6MypUjuz+I/w6G kbcEFZhHNPHVPD5UQeW4kQZ+ALcE8Iy8NjryCRKcY79/ZiI7L//qaWVqf7iwBz5Vj/ HbHWmzTqVgLoCDiLgM58Txgg4VzJh5aiBhOQnLgwSBp/wVq169FxJlqiOMYs/kh+gV N16Q+hGnx51zw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Oleg Nesterov , Christian Brauner , Sasha Levin , arnd@arndb.de, ak@linux.intel.com, kees@kernel.org Subject: [PATCH AUTOSEL 6.1 10/10] poll_wait: add mb() to fix theoretical race between waitqueue_active() and .poll() Date: Mon, 13 Jan 2025 13:35:36 -0500 Message-Id: <20250113183537.1784136-10-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250113183537.1784136-1-sashal@kernel.org> References: <20250113183537.1784136-1-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 6.1.124 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