Return-Path: Received: from fieldses.org ([174.143.236.118]:47111 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753580Ab0LCWd3 (ORCPT ); Fri, 3 Dec 2010 17:33:29 -0500 Date: Fri, 3 Dec 2010 17:33:27 -0500 From: "J. Bruce Fields" To: Alexander Viro Cc: Nick Piggin , linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH] nfsd4: allow __d_obtain_alias() to return unhashed dentries Message-ID: <20101203223326.GB28763@fieldses.org> References: <20101112184353.GA32745@fieldses.org> <20101115174837.GB10044@fieldses.org> <20101129193248.GA9897@fieldses.org> Content-Type: text/plain; charset=utf-8 In-Reply-To: Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 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? --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