Return-Path: Received: from fieldses.org ([174.143.236.118]:45157 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756300Ab0LRQQN (ORCPT ); Sat, 18 Dec 2010 11:16:13 -0500 Date: Sat, 18 Dec 2010 11:16:09 -0500 From: "J. Bruce Fields" To: Nick Piggin Cc: 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: <20101218161609.GA22150@fieldses.org> References: <20101115174837.GB10044@fieldses.org> <20101129193248.GA9897@fieldses.org> <20101203223326.GB28763@fieldses.org> <20101213051944.GA8688@amd> <20101214220102.GM24828@fieldses.org> <20101217180022.GB11515@fieldses.org> <20101218020118.GA3179@amd> Content-Type: text/plain; charset=utf-8 In-Reply-To: <20101218020118.GA3179@amd> Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 On Sat, Dec 18, 2010 at 01:01:18PM +1100, Nick Piggin wrote: > 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()? Argh, apologies; with typo fixed. --b. commit 5a911af645aae9992d465d57c397237fb35d1f93 Author: J. Bruce Fields Date: Fri Dec 17 09:05:04 2010 -0500 fs/dcache: allow __d_obtain_alias() to return unhashed dentries 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 diff --git a/fs/dcache.c b/fs/dcache.c index 5ed93cd..5c014a5 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_any_alias(inode); + 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);