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=-9.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, T_DKIMWL_WL_HIGH,USER_AGENT_GIT autolearn=ham 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 4AAEBC004C9 for ; Tue, 7 May 2019 05:51:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1C67E20675 for ; Tue, 7 May 2019 05:51:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1557208266; bh=NokzQTe48QPHBQvyu/mp0gTTSkMF3B3nNkgwopDX6Rs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=zI4dyHNNgTVzOMYd8FbzkJSDAQY7LiFiyvUww+p4NV20AMO7+tiMrqI1Mn2HLYGn2 NJ/5WA/6N6oYOJPy2jjny3hsnoayeEDV6smKrtHnhMWGJdH523cHaGn3J4wkkqyN+C mJPSjY8RtnjOwSr24R/0ZdwalnogAz59x1W5RYjE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729165AbfEGFvF (ORCPT ); Tue, 7 May 2019 01:51:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:59452 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728995AbfEGFj6 (ORCPT ); Tue, 7 May 2019 01:39:58 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9ACF0216F4; Tue, 7 May 2019 05:39:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1557207598; bh=NokzQTe48QPHBQvyu/mp0gTTSkMF3B3nNkgwopDX6Rs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZcA2Wmd2psZlcHLkUFyugE5AmFHIDHw0lC14TUe/LdMTo0a148NZuajvdVhbxtJgJ AycBnkM8VdGUFKmfkOxQqmNBs6p2xa3D4z+A47VM9TitdV2cZcUGbMytTW9bzAgdN1 Ug+AFgdsjPrG8oiVbIj99he8kHiT3KqlfjysWf78= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Miklos Szeredi , Sasha Levin , linux-fsdevel@vger.kernel.org Subject: [PATCH AUTOSEL 4.14 47/95] fuse: fix possibly missed wake-up after abort Date: Tue, 7 May 2019 01:37:36 -0400 Message-Id: <20190507053826.31622-47-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190507053826.31622-1-sashal@kernel.org> References: <20190507053826.31622-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Miklos Szeredi [ Upstream commit 2d84a2d19b6150c6dbac1e6ebad9c82e4c123772 ] In current fuse_drop_waiting() implementation it's possible that fuse_wait_aborted() will not be woken up in the unlikely case that fuse_abort_conn() + fuse_wait_aborted() runs in between checking fc->connected and calling atomic_dec(&fc->num_waiting). Do the atomic_dec_and_test() unconditionally, which also provides the necessary barrier against reordering with the fc->connected check. The explicit smp_mb() in fuse_wait_aborted() is not actually needed, since the spin_unlock() in fuse_abort_conn() provides the necessary RELEASE barrier after resetting fc->connected. However, this is not a performance sensitive path, and adding the explicit barrier makes it easier to document. Signed-off-by: Miklos Szeredi Fixes: b8f95e5d13f5 ("fuse: umount should wait for all requests") Cc: #v4.19 Signed-off-by: Sasha Levin --- fs/fuse/dev.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index 63fd33383413..af78ceead2dc 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -133,9 +133,13 @@ static bool fuse_block_alloc(struct fuse_conn *fc, bool for_background) static void fuse_drop_waiting(struct fuse_conn *fc) { - if (fc->connected) { - atomic_dec(&fc->num_waiting); - } else if (atomic_dec_and_test(&fc->num_waiting)) { + /* + * lockess check of fc->connected is okay, because atomic_dec_and_test() + * provides a memory barrier mached with the one in fuse_wait_aborted() + * to ensure no wake-up is missed. + */ + if (atomic_dec_and_test(&fc->num_waiting) && + !READ_ONCE(fc->connected)) { /* wake up aborters */ wake_up_all(&fc->blocked_waitq); } @@ -2170,6 +2174,8 @@ EXPORT_SYMBOL_GPL(fuse_abort_conn); void fuse_wait_aborted(struct fuse_conn *fc) { + /* matches implicit memory barrier in fuse_drop_waiting() */ + smp_mb(); wait_event(fc->blocked_waitq, atomic_read(&fc->num_waiting) == 0); } -- 2.20.1