linux-kernel - Re: dcache shrink list corruption?

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Date:	Sat, 3 May 2014 19:21:11 +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 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(-)

Anyway, I'm off to finish with acct.c races, then it's time for Eric's
lazy umount on unlink series; this work is getting unpleasantly close
to the areas he's touching, so I'd better get it on top of this stuff
and into -next...
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