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 X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 43732C35247 for ; Mon, 3 Feb 2020 20:59:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1DCC820CC7 for ; Mon, 3 Feb 2020 20:59:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727073AbgBCU7V (ORCPT ); Mon, 3 Feb 2020 15:59:21 -0500 Received: from mx2.suse.de ([195.135.220.15]:47744 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726272AbgBCU7V (ORCPT ); Mon, 3 Feb 2020 15:59:21 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 1DB3CACAC; Mon, 3 Feb 2020 20:59:19 +0000 (UTC) From: Roman Penyaev Cc: Roman Penyaev , Max Neunhoeffer , Jakub Kicinski , Christopher Kohlhoff , Davidlohr Bueso , Jason Baron , Andrew Morton , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/3] epoll: fix possible lost wakeup on epoll_ctl() path Date: Mon, 3 Feb 2020 21:59:05 +0100 Message-Id: <20200203205907.291929-1-rpenyaev@suse.de> X-Mailer: git-send-email 2.24.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit To: unlisted-recipients:; (no To-header on input) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org This fixes possible lost wakeup introduced by the a218cc491420. Originally modifications to ep->wq were serialized by ep->wq.lock, but in the a218cc491420 new rw lock was introduced in order to relax fd event path, i.e. callers of ep_poll_callback() function. After the change ep_modify and ep_insert (both are called on epoll_ctl() path) were switched to ep->lock, but ep_poll (epoll_wait) was using ep->wq.lock on wqueue list modification. The bug doesn't lead to any wqueue list corruptions, because wake up path and list modifications were serialized by ep->wq.lock internally, but actual waitqueue_active() check prior wake_up() call can be reordered with modification of ep ready list, thus wake up can be lost. Current patch replaces ep->wq.lock with the ep->lock for wqueue modifications, thus wake up path always observes activeness of the wqueue correcty. Fixes: a218cc491420 ("epoll: use rwlock in order to reduce ep_poll_callback() contention") References: https://bugzilla.kernel.org/show_bug.cgi?id=205933 Signed-off-by: Roman Penyaev Cc: Max Neunhoeffer Cc: Jakub Kicinski Cc: Christopher Kohlhoff Cc: Davidlohr Bueso Cc: Jason Baron Cc: Andrew Morton Cc: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org --- fs/eventpoll.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index b041b66002db..eee3c92a9ebf 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -1854,9 +1854,9 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, waiter = true; init_waitqueue_entry(&wait, current); - spin_lock_irq(&ep->wq.lock); + write_lock_irq(&ep->lock); __add_wait_queue_exclusive(&ep->wq, &wait); - spin_unlock_irq(&ep->wq.lock); + write_unlock_irq(&ep->lock); } for (;;) { @@ -1904,9 +1904,9 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, goto fetch_events; if (waiter) { - spin_lock_irq(&ep->wq.lock); + write_lock_irq(&ep->lock); __remove_wait_queue(&ep->wq, &wait); - spin_unlock_irq(&ep->wq.lock); + write_unlock_irq(&ep->lock); } return res; -- 2.24.1