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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 5248EC4360D for ; Wed, 25 Sep 2019 14:34:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 27AD32146E for ; Wed, 25 Sep 2019 14:34:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726124AbfIYOeR (ORCPT ); Wed, 25 Sep 2019 10:34:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50582 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2407656AbfIYOeR (ORCPT ); Wed, 25 Sep 2019 10:34:17 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1CF3218C8937; Wed, 25 Sep 2019 14:34:17 +0000 (UTC) Received: from bfoster (dhcp-41-2.bos.redhat.com [10.18.41.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4EB5F608C2; Wed, 25 Sep 2019 14:34:16 +0000 (UTC) Date: Wed, 25 Sep 2019 10:34:14 -0400 From: Brian Foster To: Ian Kent Cc: linux-xfs , David Howells , Dave Chinner , Al Viro , Eric Sandeen Subject: Re: [REPOST PATCH v3 09/16] xfs: mount-api - add xfs_get_tree() Message-ID: <20190925143414.GE21991@bfoster> References: <156933112949.20933.12761540130806431294.stgit@fedora-28> <156933136908.20933.15050470634891698659.stgit@fedora-28> <20190924143823.GD17688@bfoster> <3eb80542b3a247173dcef4ddf5494daa3c90e72c.camel@themaw.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.70]); Wed, 25 Sep 2019 14:34:17 +0000 (UTC) Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Wed, Sep 25, 2019 at 04:07:08PM +0800, Ian Kent wrote: > On Wed, 2019-09-25 at 15:42 +0800, Ian Kent wrote: > > On Tue, 2019-09-24 at 10:38 -0400, Brian Foster wrote: > > > On Tue, Sep 24, 2019 at 09:22:49PM +0800, Ian Kent wrote: > > > > Add the fs_context_operations method .get_tree that validates > > > > mount options and fills the super block as previously done > > > > by the file_system_type .mount method. > > > > > > > > Signed-off-by: Ian Kent > > > > --- > > > > fs/xfs/xfs_super.c | 50 > > > > ++++++++++++++++++++++++++++++++++++++++++++++++++ > > > > 1 file changed, 50 insertions(+) > > > > > > > > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c > > > > index ea3640ffd8f5..6f9fe92b4e21 100644 > > > > --- a/fs/xfs/xfs_super.c > > > > +++ b/fs/xfs/xfs_super.c > > > > @@ -1933,6 +1933,51 @@ xfs_fs_fill_super( > > > > return error; > > > > } > > > > > > > > +STATIC int > > > > +xfs_fill_super( > > > > + struct super_block *sb, > > > > + struct fs_context *fc) > > > > +{ > > > > + struct xfs_fs_context *ctx = fc->fs_private; > > > > + struct xfs_mount *mp = sb->s_fs_info; > > > > + int silent = fc->sb_flags & SB_SILENT; > > > > + int error = -ENOMEM; > > > > + > > > > + mp->m_super = sb; > > > > + > > > > + /* > > > > + * set up the mount name first so all the errors will refer to > > > > the > > > > + * correct device. > > > > + */ > > > > + mp->m_fsname = kstrndup(sb->s_id, MAXNAMELEN, GFP_KERNEL); > > > > + if (!mp->m_fsname) > > > > + return -ENOMEM; > > > > + mp->m_fsname_len = strlen(mp->m_fsname) + 1; > > > > + > > > > + error = xfs_validate_params(mp, ctx, false); > > > > + if (error) > > > > + goto out_free_fsname; > > > > + > > > > + error = __xfs_fs_fill_super(mp, silent); > > > > + if (error) > > > > + goto out_free_fsname; > > > > + > > > > + return 0; > > > > + > > > > + out_free_fsname: > > > > + sb->s_fs_info = NULL; > > > > + xfs_free_fsname(mp); > > > > + > > > > > > I'm still not following the (intended) lifecycle of mp here. > > > Looking > > > ahead in the series, we allocate mp in xfs_init_fs_context() and > > > set > > > some state. It looks like at some point we grow an xfs_fc_free() > > > callback that frees mp, but that doesn't exist as of yet. So is > > > that > > > a > > > memory leak as of this patch? > > > > > > We also call xfs_free_fsname() here (which doesn't reset pointers > > > to > > > NULL) and open-code kfree()'s of a couple of the same fields in > > > xfs_fc_free(). Those look like double frees to me. > > > > > > Hmm.. I guess I'm kind of wondering why we lift the mp alloc out of > > > the > > > fill super call in the first place. At a glance, it doesn't look > > > like > > > we > > > do anything in that xfs_init_fs_context() call that we couldn't do > > > a > > > bit > > > later.. > > > > Umm ... yes ... > > > > I think I've got the active code path right ... > > > > At this point .mount == xfs_fs_mount() which will calls > > xfs_fs_fill_super() to fill the super block. > > > > xfs_fs_fill_super() allocates the super block info struct and sets > > it in the super block private info field, then calls xfs_parseargs() > > which still allocates mp->m_fsname at this point, to accomodate a > > similar free pattern in xfs_test_remount_options(). > > > > It then calls __xfs_fs_fill_super() which doesn't touch those fsname > > fields or mp to fit in with what will be done later. > > > > If an error occurs both the fsname fields (xfs_free_fsname()) and mp > > are freed by the main caller, xfs_fs_fill_super(). > > > > I think that process is ok. > > > > The mount api process that isn't active yet is a bit different. > > > > The context (ctx), a temporary working space, is allocated then saved > > in the mount context (fc) and the super block info is also allocated > > and saved in the mount context in it's field of the same name as the > > private super block info field, s_fs_info. > > > > The function xfs_fill_super() is called as a result of the > > .get_tree() > > mount context operation to fill the super block. > > > > During this process, when the VFS successfully allocates the super > > block s_fs_info is set in the super block and the mount context > > field set to NULL. From this point freeing the private super block > > info becomes part of usual freeing of the super block with the super > > operation .kill_sb(). > > > > But if the super block allocation fails then the mount context > > s_fs_info field remains set and is the responsibility of the > > mount context operations .fc_free() method to clean up. > > > > Now the VFS calls to xfs_fill_super() after this. > > > > I should have been able to leave xfs_fill_super() it as it > > was with: > > sb->s_fs_info = NULL; > > xfs_free_fsname(mp); > > kfree(mp); > > and that should have been ok but it wasn't, there was some sort of > > allocation problem, possibly a double free, causing a crash. > > > > Strictly speaking this cleanup process should be carried out by > > either the mount context .fc_free() or super operation .kill_sb() > > and that's what I want to do. > > Umm ... but I can't actually do that ... > > Looking back at xfs I realize that the filling of the super > block is meant to leave nothing allocated and set > sb->s_fs_info = NULL on error so that ->put_super() won't try > and cleanup a whole bunch of stuff that hasn't been done. > > Which brings me back to what I originally had above ... which > we believe doesn't work ? > It looks like perhaps the assignment of sb->s_fs_info was lost as well? Skipping to the end, I see xfs_init_fs_context() alloc mp and assign fc->s_fs_info. xfs_get_tree() leads to xfs_fill_super(), which somehow gets mp from sb->s_fs_info (not fc->...), but then resets sb->s_fs_info on error and frees the names, leaving fs->s_fs_info so presumably xfs_fc_free() can free mp along with a couple of the names (again). I can't really make heads or tails of what this is even attempting to do. That aside, it's not clear to me why the new code can't follow a similar pattern as the old code with regard to allocation. Allocate mp in xfs_fill_super() and set up sb/fc pointers, reset pointers and free mp on error return. Otherwise, xfs_fc_free() checks for fc->s_fs_info != NULL and frees mp from there. Is there some reason we can't continue to do that? Brian > > > > So I'm not sure the allocation time and the place this is done > > can (or should) be done differently. > > > > And that freeing on error exit from xfs_fill_super() is definitely > > wrong now! Ha, and I didn't see any crashes myself when I tested > > it ... maybe I need a reproducer ... > > > > Ian > > > > > Brian > > > > > > > + return error; > > > > +} > > > > + > > > > +STATIC int > > > > +xfs_get_tree( > > > > + struct fs_context *fc) > > > > +{ > > > > + return vfs_get_block_super(fc, xfs_fill_super); > > > > +} > > > > + > > > > STATIC void > > > > xfs_fs_put_super( > > > > struct super_block *sb) > > > > @@ -2003,6 +2048,11 @@ static const struct super_operations > > > > xfs_super_operations = { > > > > .free_cached_objects = xfs_fs_free_cached_objects, > > > > }; > > > > > > > > +static const struct fs_context_operations xfs_context_ops = { > > > > + .parse_param = xfs_parse_param, > > > > + .get_tree = xfs_get_tree, > > > > +}; > > > > + > > > > static struct file_system_type xfs_fs_type = { > > > > .owner = THIS_MODULE, > > > > .name = "xfs", > > > > >