LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Al Viro <viro@ZenIV.linux.org.uk>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: John Ogness <john.ogness@linutronix.de>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Christoph Hellwig <hch@lst.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] fs: Teach path_connected to handle nfs filesystems with multiple roots.
Date: Thu, 15 Mar 2018 22:34:45 +0000	[thread overview]
Message-ID: <20180315223444.GA30522@ZenIV.linux.org.uk> (raw)
In-Reply-To: <87muzai6rm.fsf_-_@xmission.com>

On Wed, Mar 14, 2018 at 06:20:29PM -0500, Eric W. Biederman wrote:
> 
> On nfsv2 and nfsv3 the nfs server can export subsets of the same
> filesystem and report the same filesystem identifier, so that the nfs
> client can know they are the same filesystem.  The subsets can be from
> disjoint directory trees.  The nfsv2 and nfsv3 filesystems provides no
> way to find the common root of all directory trees exported form the
> server with the same filesystem identifier.
> 
> The practical result is that in struct super s_root for nfs s_root is
> not necessarily the root of the filesystem.  The nfs mount code sets
> s_root to the root of the first subset of the nfs filesystem that the
> kernel mounts.
> 
> This effects the dcache invalidation code in generic_shutdown_super
> currently called shrunk_dcache_for_umount and that code for years
> has gone through an additional list of dentries that might be dentry
> trees that need to be freed to accomodate nfs.
> 
> When I wrote path_connected I did not realize nfs was so special, and
> it's hueristic for avoiding calling is_subdir can fail.
> 
> The practical case where this fails is when there is a move of a
> directory from the subtree exposed by one nfs mount to the subtree
> exposed by another nfs mount.  This move can happen either locally or
> remotely.  With the remote case requiring that the move directory be cached
> before the move and that after the move someone walks the path
> to where the move directory now exists and in so doing causes the
> already cached directory to be moved in the dcache through the magic
> of d_splice_alias.
> 
> If someone whose working directory is in the move directory or a
> subdirectory and now starts calling .. from the initial mount of nfs
> (where s_root == mnt_root), then path_connected as a heuristic will
> not bother with the is_subdir check.  As s_root really is not the root
> of the nfs filesystem this heuristic is wrong, and the path may
> actually not be connected and path_connected can fail.
> 
> The is_subdir function might be cheap enough that we can call it
> unconditionally.  Verifying that will take some benchmarking and
> the result may not be the same on all kernels this fix needs
> to be backported to.  So I am avoiding that for now.
> 
> Filesystems with snapshots such as nilfs and btrfs do something
> similar.  But as the directory tree of the snapshots are disjoint
> from one another and from the main directory tree rename won't move
> things between them and this problem will not occur.
> 
> Cc: stable@vger.kernel.org
> Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
> Fixes: 397d425dc26d ("vfs: Test for and handle paths that are unreachable from their mnt_root")
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
> 
> Al do you want to push this one to Linus or shall I?

Applied; I think there might be a helper lurking in there, but for now
that'll do.

  reply	other threads:[~2018-03-15 22:34 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-22 23:50 [PATCH v2 0/6] fs/dcache: avoid trylock loops John Ogness
2018-02-22 23:50 ` [PATCH v2 1/6] fs/dcache: Remove stale comment from dentry_kill() John Ogness
2018-02-22 23:50 ` [PATCH v2 2/6] fs/dcache: Move dentry_kill() below lock_parent() John Ogness
2018-02-22 23:50 ` [PATCH v2 3/6] fs/dcache: Avoid the try_lock loop in d_delete() John Ogness
2018-02-23  2:08   ` Al Viro
2018-02-22 23:50 ` [PATCH v2 4/6] fs/dcache: Avoid the try_lock loops in dentry_kill() John Ogness
2018-02-23  2:22   ` Al Viro
2018-02-23  3:12     ` Al Viro
2018-02-23  3:16       ` Al Viro
2018-02-23  5:46       ` Al Viro
2018-02-22 23:50 ` [PATCH v2 5/6] fs/dcache: Avoid a try_lock loop in shrink_dentry_list() John Ogness
2018-02-23  3:48   ` Al Viro
2018-02-22 23:50 ` [PATCH v2 6/6] fs/dcache: Avoid remaining " John Ogness
2018-02-23  3:58   ` Al Viro
2018-02-23  4:08     ` Al Viro
2018-02-23 13:57       ` John Ogness
2018-02-23 15:09         ` Al Viro
2018-02-23 17:42           ` Al Viro
2018-02-23 20:13             ` [BUG] lock_parent() breakage when used from shrink_dentry_list() (was Re: [PATCH v2 6/6] fs/dcache: Avoid remaining try_lock loop in shrink_dentry_list()) Al Viro
2018-02-23 21:35               ` Linus Torvalds
2018-02-24  0:22                 ` Al Viro
2018-02-25  7:40                   ` Al Viro
2018-02-27  5:16                     ` dcache: remove trylock loops (was Re: [BUG] lock_parent() breakage when used from shrink_dentry_list()) John Ogness
2018-03-12 19:13                       ` Al Viro
2018-03-12 20:05                         ` Al Viro
2018-03-12 20:33                           ` Al Viro
2018-03-13  1:12                           ` NeilBrown
2018-04-28  0:10                             ` Al Viro
2018-03-12 20:23                         ` Eric W. Biederman
2018-03-12 20:39                           ` Al Viro
2018-03-12 23:28                             ` Eric W. Biederman
2018-03-12 23:52                               ` Eric W. Biederman
2018-03-13  0:37                                 ` Al Viro
2018-03-13  0:50                                   ` Al Viro
2018-03-13  4:02                                     ` Eric W. Biederman
2018-03-14 23:20                                     ` [PATCH] fs: Teach path_connected to handle nfs filesystems with multiple roots Eric W. Biederman
2018-03-15 22:34                                       ` Al Viro [this message]
2018-03-13  0:36                               ` dcache: remove trylock loops (was Re: [BUG] lock_parent() breakage when used from shrink_dentry_list()) Al Viro
2018-03-12 22:14                         ` Thomas Gleixner
2018-03-13 20:46                         ` John Ogness
2018-03-13 21:05                           ` John Ogness
2018-03-13 23:59                             ` Al Viro
2018-03-14  2:58                               ` Matthew Wilcox
2018-03-14  8:18                               ` John Ogness
2018-03-02  9:04                     ` [BUG] lock_parent() breakage when used from shrink_dentry_list() (was Re: [PATCH v2 6/6] fs/dcache: Avoid remaining try_lock loop in shrink_dentry_list()) Sebastian Andrzej Siewior
2018-02-23  0:59 ` [PATCH v2 0/6] fs/dcache: avoid trylock loops Linus Torvalds

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180315223444.GA30522@ZenIV.linux.org.uk \
    --to=viro@zeniv.linux.org.uk \
    --cc=bigeasy@linutronix.de \
    --cc=ebiederm@xmission.com \
    --cc=hch@lst.de \
    --cc=john.ogness@linutronix.de \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    --cc=torvalds@linux-foundation.org \
    --subject='Re: [PATCH] fs: Teach path_connected to handle nfs filesystems with multiple roots.' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).