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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_MUTT 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 E6B65C04AAF for ; Sat, 18 May 2019 20:04:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C03BC20833 for ; Sat, 18 May 2019 20:04:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727620AbfERUEL (ORCPT ); Sat, 18 May 2019 16:04:11 -0400 Received: from fieldses.org ([173.255.197.46]:55060 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725950AbfERUEL (ORCPT ); Sat, 18 May 2019 16:04:11 -0400 Received: by fieldses.org (Postfix, from userid 2815) id 535441C81; Sat, 18 May 2019 16:04:11 -0400 (EDT) Date: Sat, 18 May 2019 16:04:11 -0400 To: "J. Bruce Fields" Cc: linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 1/2] nfsd: allow fh_want_write to be called twice Message-ID: <20190518200411.GB32684@fieldses.org> References: <1557969619-17157-1-git-send-email-bfields@redhat.com> <1557969619-17157-2-git-send-email-bfields@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1557969619-17157-2-git-send-email-bfields@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) From: bfields@fieldses.org (J. Bruce Fields) Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org Ugh, sorry, ignore the two old patches that got sent with the new series. --b. On Wed, May 15, 2019 at 09:20:06PM -0400, J. Bruce Fields wrote: > 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; > -- > 2.21.0