Return-Path: Received: from ipmail06.adl2.internode.on.net ([150.101.137.129]:24199 "EHLO ipmail06.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750903Ab0LMFTu (ORCPT ); Mon, 13 Dec 2010 00:19:50 -0500 Date: Mon, 13 Dec 2010 16:19:44 +1100 From: Nick Piggin To: "J. Bruce Fields" Cc: Alexander Viro , Nick Piggin , linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] nfsd4: allow __d_obtain_alias() to return unhashed dentries Message-ID: <20101213051944.GA8688@amd> References: <20101112184353.GA32745@fieldses.org> <20101115174837.GB10044@fieldses.org> <20101129193248.GA9897@fieldses.org> <20101203223326.GB28763@fieldses.org> Content-Type: text/plain; charset=iso-8859-1 In-Reply-To: <20101203223326.GB28763@fieldses.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 On Fri, Dec 03, 2010 at 05:33:27PM -0500, J. Bruce Fields wrote: > From: J. Bruce Fields > > Without this patch > > ? ? ? ?client$ mount -tnfs4 server:/export/ /mnt/ > ? ? ? ?client$ tail -f /mnt/FOO > ? ? ? ?... > ? ? ? ?server$ df -i /export > ? ? ? ?server$ rm /export/FOO > ? ? ? ?(^C the tail -f) > ? ? ? ?server$ df -i /export > ? ? ? ?server$ echo 2 >/proc/sys/vm/drop_caches > ? ? ? ?server$ 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. ?On-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: > > ? ? ? ?- putfh: look up the filehandle. ?The only alias found for the > ? ? ? ? ?inode will be DCACHE_UNHASHED alias referenced by the filp > ? ? ? ? ?associated with the nfsd open. ?d_obtain_alias() doesn't like > ? ? ? ? ?this, so it creates a new DCACHE_DISCONECTED dentry and > ? ? ? ? ?returns 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 > Signed-off-by: J. Bruce Fields > --- > 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 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 wrote: > > >> > On Tue, Nov 16, 2010 at 4:48 AM, J. Bruce Fields 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? > > >> >>> > > >> >>> - ? ? ? ? ? ? ? if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) { > > >> >>> + ? ? ? ? ? ? ? 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? ?Could 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? Not sure where Al's hiding... But I would like to update the comments, and perhaps even a new add a new function here (or new flag to __d_find_alias). AFAIKS, the callers are OK, however I suppose d_splice_alias and d_materialise_unique should not have unlinked inodes at this point, so at least a BUG_ON for them might be a good idea? > > --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;