Re: dcache shrink list corruption?

From: Al Viro
Date: Sun May 04 2014 - 02:29:41 EST


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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