Return-Path: Received: from ipmail06.adl2.internode.on.net ([150.101.137.129]:60555 "EHLO ipmail06.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756907Ab0LRCBZ (ORCPT ); Fri, 17 Dec 2010 21:01:25 -0500 Date: Sat, 18 Dec 2010 13:01:18 +1100 From: Nick Piggin To: "J. Bruce Fields" Cc: Nick Piggin , Alexander Viro , Nick Piggin , linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 2/2] fs/dcache: allow __d_obtain_alias() to return unhashed dentries Message-ID: <20101218020118.GA3179@amd> References: <20101115174837.GB10044@fieldses.org> <20101129193248.GA9897@fieldses.org> <20101203223326.GB28763@fieldses.org> <20101213051944.GA8688@amd> <20101214220102.GM24828@fieldses.org> <20101217180022.GB11515@fieldses.org> Content-Type: text/plain; charset=iso-8859-1 In-Reply-To: <20101217180022.GB11515@fieldses.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 On Fri, Dec 17, 2010 at 01:00:23PM -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. > > Leave __d_find_alias() alone to avoid changing behavior of other > callers. > > Also nfsd doesn't need all the checks of __d_find_alias(); any dentry, > hashed or unhashed, disconnected or not, should work. > > Signed-off-by: J. Bruce Fields > --- > fs/dcache.c | 26 ++++++++++++++++++++++++-- > 1 files changed, 24 insertions(+), 2 deletions(-) > > On Tue, Dec 14, 2010 at 05:01:02PM -0500, J. Bruce Fields wrote: > > On Mon, Dec 13, 2010 at 04:19:44PM +1100, Nick Piggin wrote: > > > 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? > > > > That does sound safer. I'm pretty confused by the various > > __di_splice_alias callers. I'll go search through them and see if I can > > understand better.... > > I think a new __d_find_alias flag would just make it more confusing. > And it looks like all d_obtain_alias needs is something much simpler. > This works for me. Well I don't really know if this is clearer. By convention, __ prefix version should be same as non prefix version but just take fewer locks. Why do you have the new d_find_any_alias()? > > --b. > > diff --git a/fs/dcache.c b/fs/dcache.c > index 5ed93cd..d5f9da4 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -1135,6 +1135,28 @@ static inline struct hlist_head *d_hash(struct dentry *parent, > return dentry_hashtable + (hash & D_HASHMASK); > } > > +static struct dentry * __d_find_any_alias(struct inode *inode) > +{ > + struct dentry *alias; > + > + if (list_empty(&inode->i_dentry)) > + return NULL; > + alias = list_first_entry(&inode->i_dentry, struct dentry, d_alias); > + __dget_locked(alias); > + return alias; > +} > + > +static struct dentry * d_find_any_alias(struct inode *inode) > +{ > + struct dentry *de; > + > + spin_lock(&dcache_lock); > + de = __d_find_alias(inode, 0); > + spin_unlock(&dcache_lock); > + return de; > +} > + > + > /** > * d_obtain_alias - find or allocate a dentry for a given inode > * @inode: inode to allocate the dentry for > @@ -1164,7 +1186,7 @@ struct dentry *d_obtain_alias(struct inode *inode) > if (IS_ERR(inode)) > return ERR_CAST(inode); > > - res = d_find_alias(inode); > + res = d_find_any_alias(inode); > if (res) > goto out_iput; > > @@ -1176,7 +1198,7 @@ struct dentry *d_obtain_alias(struct inode *inode) > tmp->d_parent = tmp; /* make sure dput doesn't croak */ > > spin_lock(&dcache_lock); > - res = __d_find_alias(inode, 0); > + res = __d_find_any_alias(inode); > if (res) { > spin_unlock(&dcache_lock); > dput(tmp); > -- > 1.7.1