On Thu, Nov 29, 2012 at 08:06:12PM +0000, Al Viro wrote:
> On Tue, Sep 25, 2012 at 04:29:58AM -0700, Eric W. Biederman wrote:
> > Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx> writes:
> >
> > >> Could you try the following patch? This should report what directories
> > >> cannot be renamed because one of them is a mount point and it gives some
> > >> real insight into what is going on.
> > >
> > > ls /
> > > __d_unalias: /dev -> /dev
> > > __d_unalias: /proc -> /proc
> > > __d_unalias: /sys -> /sys
> >
> > Ok. That is what I thought was going on. For some reason nfs is
> > attempting to recreate an existing dentry.
> >
> > Does this fix the nfs problem for you?
> >
> > Eric
> >
> > diff --git a/fs/dcache.c b/fs/dcache.c
> > index 8086636..6390f0f 100644
> > --- a/fs/dcache.c
> > +++ b/fs/dcache.c
> > @@ -2404,6 +2404,9 @@ out_unalias:
> > if (likely(!d_mountpoint(alias))) {
> > __d_move(alias, dentry);
> > ret = alias;
> > + } else if ((alias->d_parent == dentry->d_parent) &&
> > + !dentry_cmp(alias, dentry->d_name.name, dentry->d_name.len))
> > + ret = alias;
> > }
>
> The interesting question is why the hell had it decided that preexisting
> dentry was not good enough for it? Note that we have arrived to nfs_lookup()
> after we'd decided *not* to use the damn alias. The trace posted upthread
> went __lookup_hash() -> lookup_real(). It means that lookup_dcache()
> has not produced this one. And no, even if ->d_revalidate() decided it
> was no good, the logics in d_invalidate() would've said "busy" and we'd
> gone with that dentry anyway. So it means that d_lookup() has not
> found it at all.
>
> IOW, something out there is blindly unhashing mountpoint dentries; that's
> where the real root of the problem seems to be. Could you slap
> WARN_ON(d_mountpoint(dentry)) in __d_drop() and see what it catches?
Ho-hum... nfs_prime_dcache() seems to be the likely suspect. What happens
if we get nfs_same_file() failing for some reason for a mountpoint there?
Or for a busy directory, for that matter...
Guys, could somebody with reproducer see if we step into the else side of
if (nfs_same_file(dentry, entry)) {
nfs_refresh_inode(dentry->d_inode, entry->fattr);
goto out;
} else {
d_drop(dentry);
dput(dentry);
}
in nfs_prime_dcache() with dentry being a mountpoint? If nothing else,
I would suggest replacing that d_drop(dentry) with
if (d_invalidate(dentry) != 0)
goto out;
in there.
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