From: J. Bruce Fields <bfields@xxxxxxxxxx>
Without this patch
   Âclient$ mount -tnfs4 server:/export/ /mnt/
   Âclient$ tail -f /mnt/FOO
   Â...
   Âserver$ df -i /export
   Âserver$ rm /export/FOO
   Â(^C the tail -f)
   Âserver$ df -i /export
   Âserver$ echo 2 >/proc/sys/vm/drop_caches
   Âserver$ df -i /export
the df's will show that the inode is not freed on the filesystem until
the last step, when it could have been freed after killing the client's
tail -f. ÂOn-disk data won't be deallocated either, leading to possible
spurious ENOSPC.
This occurs because when the client does the close, it arrives in a
compound with a putfh and a close, processed like:
   Â- putfh: look up the filehandle. ÂThe only alias found for the
    Âinode will be DCACHE_UNHASHED alias referenced by the filp
    Âassociated with the nfsd open. Âd_obtain_alias() doesn't like
    Âthis, so it creates a new DCACHE_DISCONECTED dentry and
    Âreturns that instead.
Nick Piggin suggested fixing this by allowing d_obtain_alias to return
the unhashed dentry that is referenced by the filp, instead of making it
create a new dentry.
Cc: Nick Piggin <npiggin@xxxxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
---
fs/dcache.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
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:
> >> >>> 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.
So here's a version with a changelog; objections?
--b.
diff --git a/fs/dcache.c b/fs/dcache.c
index 23702a9..afa8a0d 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -368,7 +368,7 @@ static struct dentry * __d_find_alias(struct inode *inode, int want_discon)
next = tmp->next;
prefetch(next);
alias = list_entry(tmp, struct dentry, d_alias);
- if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
+ if (S_ISDIR(inode->i_mode) || !inode->i_nlink || !d_unhashed(alias)) {
if (IS_ROOT(alias) &&
(alias->d_flags & DCACHE_DISCONNECTED))
discon_alias = alias;
--
1.7.1
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