On Tue, Nov 30, 2010 at 12:00:16PM +1100, Nick Piggin wrote:
> On Tue, Nov 30, 2010 at 6:32 AM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
> > On Mon, Nov 29, 2010 at 02:56:22PM +1100, Nick Piggin wrote:
> >> On Tue, Nov 16, 2010 at 5:45 PM, Nick Piggin <npiggin@xxxxxxxxx> wrote:
> >> > On Tue, Nov 16, 2010 at 4:48 AM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
> >> >> On Sat, Nov 13, 2010 at 10:53:12PM +1100, Nick Piggin wrote:
> >> >>> On Sat, Nov 13, 2010 at 5:43 AM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
> >> >
> >> >>> > Â Â Â Â- putfh: look up the filehandle. ÂThe only alias found for the
> >> >>> > Â Â Â Â Âinode will be DCACHE_UNHASHED alias referenced by the filp
> >> >>> > Â Â Â Â Âassociated with the nfsd open. Âd_obtain_alias() doesn't like
> >> >>> > Â Â Â Â Âthis, so it creates a new DCACHE_DISCONECTED dentry and
> >> >>> > Â Â Â Â Âreturns that instead.
> >> >>>
> >> >>> This seems to be where the thing goes wrong. It isn't a hashed dentry at
> >> >>> this point here, so d_obtain_alias should not be making one.
> >> >>
> >> >> Sounds sensible. Â(But can you think of any actual bugs that will result
> >> >> from trying to add a new hashed dentry in this case?)
> >> >
> >> > Well, this one? :)
> >> >
> >> >
> >> >>> I think the inode i_nlink games are much more appropriate on this side of
> >> >>> the equation, rather than the dput side (after all, d_obtain_alias is setting
> >> >>> up an alias for the inode).
> >> >>>
> >> >>> Can you even put the link check into __d_find_alias?
> >> >>>
> >> >>> - Â Â Â Â Â Â Â if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
> >> >>> + Â Â Â Â Â Â Â if (S_ISDIR(inode->i_mode) || !inode->i_nlink ||
> >> >>> !d_unhashed(alias)) {
> >> >>>
> >> >>> Something like that?
> >> >>
> >> >> The immediate result of that would be for the close rpc (or any rpc's
> >> >> sent after the file was unlinked) to fail with ESTALE.
> >> >
> >> > Why is that? Seems like it would be a bug, because a hashed dentry may
> >> > be unhashed at any time concurrently to nfsd operation, so it should be
> >> > able to tolerate that so long as it has a ref on the inode?
> >>
> >> Ping? Did you work out why nfs fails with ESTALE in that case? It seems
> >> to work in my testing (and do the right thing with freeing the inode).
> >
> > Bah, sorry, I read too quickly, got the sense of the test backwards, and
> > thought you were suggesting __d_find_alias() shouldn't return an alias
> > in the i_nlink == 0 case!
> >
> > Yes, agreed, that should solve my problem.
>
> OK, good.
>
> > But what's the reason for the d_unhashed() check now? ÂCould we get rid
> > of it entirely?
>
> Well when the inode still has links I think we actually do want any new
> references to go to hashed dentries. Definitely for d_splice_alias.
OK, makes sense. Should we stick a changelog on it and pass it along to
someone?
--b.
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