From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C200DC4332F for ; Thu, 27 Jan 2022 18:10:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238332AbiA0SKx (ORCPT ); Thu, 27 Jan 2022 13:10:53 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45214 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245166AbiA0SKH (ORCPT ); Thu, 27 Jan 2022 13:10:07 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 922D9C061714; Thu, 27 Jan 2022 10:09:45 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 522CEB818E1; Thu, 27 Jan 2022 18:09:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 911CAC340E4; Thu, 27 Jan 2022 18:09:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1643306983; bh=hnC+WHQSB5Y9GOv0QCFpDjFeMVtgDx2Tl+exIvMj6zU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=XzcAQlxZCLoq1MSbmtAx3Y+uT6yCoEs9ND8/nRokwi5HFKFiY/SPQCukkeHChXk8K e0lLyx3E8pXCiAzLxjJz/zMLeAlfYeHGZkcmz/ogn4dDpgG5N3PeINSp4PaTZleEAJ sKpHo2n2TFZ72v2RMcQemJGwc8orSqeV8xnYmO1c= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Linus Torvalds , Jan Kara Subject: [PATCH 5.4 11/11] select: Fix indefinitely sleeping task in poll_schedule_timeout() Date: Thu, 27 Jan 2022 19:09:12 +0100 Message-Id: <20220127180258.742791870@linuxfoundation.org> X-Mailer: git-send-email 2.35.0 In-Reply-To: <20220127180258.362000607@linuxfoundation.org> References: <20220127180258.362000607@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jan Kara commit 68514dacf2715d11b91ca50d88de047c086fea9c upstream. A task can end up indefinitely sleeping in do_select() -> poll_schedule_timeout() when the following race happens: TASK1 (thread1) TASK2 TASK1 (thread2) do_select() setup poll_wqueues table with 'fd' write data to 'fd' pollwake() table->triggered = 1 closes 'fd' thread1 is waiting for poll_schedule_timeout() - sees table->triggered table->triggered = 0 return -EINTR loop back in do_select() But at this point when TASK1 loops back, the fdget() in the setup of poll_wqueues fails. So now so we never find 'fd' is ready for reading and sleep in poll_schedule_timeout() indefinitely. Treat an fd that got closed as a fd on which some event happened. This makes sure cannot block indefinitely in do_select(). Another option would be to return -EBADF in this case but that has a potential of subtly breaking applications that excercise this behavior and it happens to work for them. So returning fd as active seems like a safer choice. Suggested-by: Linus Torvalds CC: stable@vger.kernel.org Signed-off-by: Jan Kara Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- fs/select.c | 63 +++++++++++++++++++++++++++++++----------------------------- 1 file changed, 33 insertions(+), 30 deletions(-) --- a/fs/select.c +++ b/fs/select.c @@ -458,9 +458,11 @@ get_max: return max; } -#define POLLIN_SET (EPOLLRDNORM | EPOLLRDBAND | EPOLLIN | EPOLLHUP | EPOLLERR) -#define POLLOUT_SET (EPOLLWRBAND | EPOLLWRNORM | EPOLLOUT | EPOLLERR) -#define POLLEX_SET (EPOLLPRI) +#define POLLIN_SET (EPOLLRDNORM | EPOLLRDBAND | EPOLLIN | EPOLLHUP | EPOLLERR |\ + EPOLLNVAL) +#define POLLOUT_SET (EPOLLWRBAND | EPOLLWRNORM | EPOLLOUT | EPOLLERR |\ + EPOLLNVAL) +#define POLLEX_SET (EPOLLPRI | EPOLLNVAL) static inline void wait_key_set(poll_table *wait, unsigned long in, unsigned long out, unsigned long bit, @@ -527,6 +529,7 @@ static int do_select(int n, fd_set_bits break; if (!(bit & all_bits)) continue; + mask = EPOLLNVAL; f = fdget(i); if (f.file) { wait_key_set(wait, in, out, bit, @@ -534,34 +537,34 @@ static int do_select(int n, fd_set_bits mask = vfs_poll(f.file, wait); fdput(f); - if ((mask & POLLIN_SET) && (in & bit)) { - res_in |= bit; - retval++; - wait->_qproc = NULL; - } - if ((mask & POLLOUT_SET) && (out & bit)) { - res_out |= bit; - retval++; - wait->_qproc = NULL; - } - if ((mask & POLLEX_SET) && (ex & bit)) { - res_ex |= bit; - retval++; - wait->_qproc = NULL; - } - /* got something, stop busy polling */ - if (retval) { - can_busy_loop = false; - busy_flag = 0; - - /* - * only remember a returned - * POLL_BUSY_LOOP if we asked for it - */ - } else if (busy_flag & mask) - can_busy_loop = true; - } + if ((mask & POLLIN_SET) && (in & bit)) { + res_in |= bit; + retval++; + wait->_qproc = NULL; + } + if ((mask & POLLOUT_SET) && (out & bit)) { + res_out |= bit; + retval++; + wait->_qproc = NULL; + } + if ((mask & POLLEX_SET) && (ex & bit)) { + res_ex |= bit; + retval++; + wait->_qproc = NULL; + } + /* got something, stop busy polling */ + if (retval) { + can_busy_loop = false; + busy_flag = 0; + + /* + * only remember a returned + * POLL_BUSY_LOOP if we asked for it + */ + } else if (busy_flag & mask) + can_busy_loop = true; + } if (res_in) *rinp = res_in;