linux-kernel - Re: dcache shrink list corruption?

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Date:	Sun, 4 May 2014 07:29:15 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	Dave Chinner <david@...morbit.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: dcache shrink list corruption?

On Sat, May 03, 2014 at 07:21:11PM +0100, Al Viro wrote:
> On Sat, May 03, 2014 at 05:26:04AM +0100, Al Viro wrote:
> 
> > See vfs.git#dentry_kill-3; warning - this is completely untested and I would
> > really like comments on spinning case there (i.e. the one where select_collect()
> > finds some stuff already on some other shrink list and nothing with zero
> > refcount that wouldn't be there).  In that case (and it's basically "somebody
> > else is evicting stuff in our subtree and they'd already picked everything
> > we want evicted") I just let the loop in check_submounts_and_drop() repeat
> > (we do have cond_resched() there).  Any better suggestions would be welcome...
> 
> Hmm...  As the matter of fact, the whole shrink_dcache_for_umount() could
> be made a lot saner.  What we need is to reuse shrink_dcache_parent()
> and follow it with d_walk() that would just go through whatever remains and
> complain about the leaves of that.  For anon roots we'll obviously need to
> wrap that into dget and d_drop/dput.
> 
> I'm testing that right now; everything seems to be working so far and if
> it survives, I'll push that sucker out.  Total since the beginning of
> the whole series:
>  fs/dcache.c            |  310 ++++++++++++++++++++++++++++++++---------------------------------------------------------
>  include/linux/dcache.h |    2 +
>  2 files changed, 112 insertions(+), 200 deletions(-)

No regressions compared to mainline; force-pushed into vfs#dentry_kill-3.
Review and testing would be very welcome...  Summary for that branch:
(it's *not* a pull request yet; the thing really needs review)
Shortlog:
Al Viro (8):
      fix races between __d_instantiate() and checks of dentry flags
      fold d_kill() and d_free()
      fold try_prune_one_dentry()
      new helper: dentry_free()
      expand the call of dentry_lru_del() in dentry_kill()
      dentry_kill(): don't try to remove from shrink list
      don't remove from shrink list in select_collect()
      more graceful recovery in umount_collect()

Miklos Szeredi (1):
      dcache: don't need rcu in shrink_dentry_list()

Diffstat:
 fs/dcache.c            |  318 +++++++++++++++++++++++++++++------------------------------------------------------------
 fs/namei.c             |    6 +-
 include/linux/dcache.h |    2 +
 3 files changed, 107 insertions(+), 219 deletions(-)

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