From patchwork Tue Mar 19 00:33:24 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 10858663 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E00501575 for ; Tue, 19 Mar 2019 00:33:34 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C01A32941A for ; Tue, 19 Mar 2019 00:33:34 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B4A7F29558; Tue, 19 Mar 2019 00:33:34 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 4E6C9294BF for ; Tue, 19 Mar 2019 00:33:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726639AbfCSAdd (ORCPT ); Mon, 18 Mar 2019 20:33:33 -0400 Received: from mx2.suse.de ([195.135.220.15]:37208 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726575AbfCSAdd (ORCPT ); Mon, 18 Mar 2019 20:33:33 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 3A8E9ADD4; Tue, 19 Mar 2019 00:33:32 +0000 (UTC) From: NeilBrown To: Trond Myklebust , Anna Schumaker Date: Tue, 19 Mar 2019 11:33:24 +1100 Cc: Chuck Lever , linux-nfs@vger.kernel.org Subject: [PATCH] NFS: fix mount/umount race in nlmclnt. Message-ID: <877ecv8zzf.fsf@notabene.neil.brown.name> MIME-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP If the last NFSv3 unmount from a given host races with a mount from the same host, we can destroy an nlm_host that is still in use. Specifically nlmclnt_lookup_host() can increment h_count on an nlm_host that nlmclnt_release_host() has just successfully called refcount_dec_and_test() on. Once nlmclnt_lookup_host() drops the mutex, nlm_destroy_host_lock() will be called to destroy the nlmclnt which is now in use again. The cause of the problem is that the dec_and_test happens outside the locked region. This is easily fixed by using refcount_dec_and_mutex_lock(). Fixes: 8ea6ecc8b075 ("lockd: Create client-side nlm_host cache") Cc: stable@vger.kernel.org (v2.6.38+) Signed-off-by: NeilBrown --- fs/lockd/host.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/fs/lockd/host.c b/fs/lockd/host.c index 93fb7cf0b92b..f0b5c987d6ae 100644 --- a/fs/lockd/host.c +++ b/fs/lockd/host.c @@ -290,12 +290,11 @@ void nlmclnt_release_host(struct nlm_host *host) WARN_ON_ONCE(host->h_server); - if (refcount_dec_and_test(&host->h_count)) { + if (refcount_dec_and_mutex_lock(&host->h_count, &nlm_host_mutex)) { WARN_ON_ONCE(!list_empty(&host->h_lockowners)); WARN_ON_ONCE(!list_empty(&host->h_granted)); WARN_ON_ONCE(!list_empty(&host->h_reclaim)); - mutex_lock(&nlm_host_mutex); nlm_destroy_host_locked(host); mutex_unlock(&nlm_host_mutex); }