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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,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 5294AC47253 for ; Fri, 1 May 2020 13:27:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2A10D2173E for ; Fri, 1 May 2020 13:27:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588339640; bh=baC/hUKXrxs/tjNcbhgr2gs9AikJqaDGQ8pWgO2QMMI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=jpqPiBvJ18+2RgUjqrcCp30ai8nI/p++Hhk4P62LRBJzryHJnWp8TZN+ugYndLbvN wBW5E9TYpQ4bXZJEL/cso3JyFHqJNjURXHyIWKDfVhGg4Na8//Trt+RzMiIEdz/Iay HJ9HfcUfrXKRlK/T5aWnf2KxYTKQHLvvL2AJR4gs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729445AbgEAN1S (ORCPT ); Fri, 1 May 2020 09:27:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:49366 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729425AbgEAN1N (ORCPT ); Fri, 1 May 2020 09:27:13 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 73442208D6; Fri, 1 May 2020 13:27:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588339632; bh=baC/hUKXrxs/tjNcbhgr2gs9AikJqaDGQ8pWgO2QMMI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iQbyZSMG6HqgvUIFrz/tGFufjuY5fNxaMAjjKJ/udNpgUJcccRb54QWmZAm4Qg8L7 ks95qPcVzv5x3R9qVYDCL4zWxnlv4IdB4mm1TZASR7KYPddQweuA+z5s1Iw8oiuhxi +c7ZocvGu9569sxp1oE/MsiJgdppNY4mf0x3L+rU= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Miklos Szeredi , Guenter Roeck Subject: [PATCH 4.4 56/70] fuse: fix possibly missed wake-up after abort Date: Fri, 1 May 2020 15:21:44 +0200 Message-Id: <20200501131530.296926543@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200501131513.302599262@linuxfoundation.org> References: <20200501131513.302599262@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Miklos Szeredi commit 2d84a2d19b6150c6dbac1e6ebad9c82e4c123772 upstream. 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 Cc: Guenter Roeck Signed-off-by: Greg Kroah-Hartman --- fs/fuse/dev.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -145,9 +145,13 @@ static bool fuse_block_alloc(struct fuse 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); } @@ -2222,6 +2226,8 @@ 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); }