Re: [PATCH] Busy inodes after unmount, be more verbose in generic_shutdown_super

[Kirill Korotaev <dev@sw.ru>]

> > On Tue, Jan 17, Kirill Korotaev wrote:
> >
> >
> > > Olaf, can you please check if my patch for busy inodes from -mm tree 
> > > helps you?
> > > Patch name is fix-of-dcache-race-leading-to-busy-inodes-on-umount.patch
> > > http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.15/2.6.15-mm4/broken-out/fix-of-dcache-race-leading-to-busy-inodes-on-umount.patch
> >
> > This patch is just wrong. It is hiding bugs in file systems. The problem is
> > that somewhere the reference counting on the vfsmount objects is wrong. The
> > file system is unmounted before the last dentry is dereferenced. Either you
> > didn't hold a reference to the proper vfsmount objects at all or you
> > dereference it too early. See Al Viros patch series (search for "namei fixes")
> > on how to fix this issues.
>
>
> The only reason I've been carrying that patch is as a reminder that there's
> a bug that we need to fix.  It'd be good news if that bug had been fixed by
> other means.
>
> Kirill, do you know whether the bug is still present in 2.6.16-rc1?

it exists in 2.6.15 and I see no changes in 2.6.16-rc1 except for 
cosmetics :(
checked the git tree, dput() etc. the bug is definetely still here - 
nothing changed in this area.

Sorry for bad news.

The patch can be probably remade via introducing "notlocked_refs" 
counter on dentry. if shrinker()/umount() see such a dentry() with 
non-zero refcnt it can sleep as it is done in current patch. It would be 
a little bit cleaner/simpler. What do you think?
If someone suggest any brilliant/helpfull idea I would be happy to 
improve it.

Kirill

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