From patchwork Thu May 16 01:20:06 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Bruce Fields X-Patchwork-Id: 10945437 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 0B897912 for ; Thu, 16 May 2019 01:46:35 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id ECDD72874A for ; Thu, 16 May 2019 01:46:34 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id DFB51288AD; Thu, 16 May 2019 01:46:34 +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 D2F302874A for ; Thu, 16 May 2019 01:46:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727322AbfEPBq0 (ORCPT ); Wed, 15 May 2019 21:46:26 -0400 Received: from fieldses.org ([173.255.197.46]:33068 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726996AbfEPBUX (ORCPT ); Wed, 15 May 2019 21:20:23 -0400 Received: by fieldses.org (Postfix, from userid 2815) id 4BAF88BF; Wed, 15 May 2019 21:20:23 -0400 (EDT) From: "J. Bruce Fields" To: linux-nfs@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, "J. Bruce Fields" Subject: [PATCH 1/2] nfsd: allow fh_want_write to be called twice Date: Wed, 15 May 2019 21:20:06 -0400 Message-Id: <1557969619-17157-2-git-send-email-bfields@redhat.com> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <1557969619-17157-1-git-send-email-bfields@redhat.com> References: <1557969619-17157-1-git-send-email-bfields@redhat.com> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: "J. Bruce Fields" A fuzzer recently triggered lockdep warnings about potential sb_writers deadlocks caused by fh_want_write(). Looks like we aren't careful to pair each fh_want_write() with an fh_drop_write(). It's not normally a problem since fh_put() will call fh_drop_write() for us. And was OK for NFSv3 where we'd do one operation that might call fh_want_write(), and then put the filehandle. But an NFSv4 protocol fuzzer can do weird things like call unlink twice in a compound, and then we get into trouble. I'm a little worried about this approach of just leaving everything to fh_put(). But I think there are probably a lot of fh_want_write()/fh_drop_write() imbalances so for now I think we need it to be more forgiving. Signed-off-by: J. Bruce Fields --- fs/nfsd/vfs.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h index a7e107309f76..db351247892d 100644 --- a/fs/nfsd/vfs.h +++ b/fs/nfsd/vfs.h @@ -120,8 +120,11 @@ void nfsd_put_raparams(struct file *file, struct raparms *ra); static inline int fh_want_write(struct svc_fh *fh) { - int ret = mnt_want_write(fh->fh_export->ex_path.mnt); + int ret; + if (fh->fh_want_write) + return 0; + ret = mnt_want_write(fh->fh_export->ex_path.mnt); if (!ret) fh->fh_want_write = true; return ret;