Return-Path: Received: from fieldses.org ([174.143.236.118]:46084 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752168Ab1ARUpR (ORCPT ); Tue, 18 Jan 2011 15:45:17 -0500 Date: Tue, 18 Jan 2011 15:45:09 -0500 From: "J. Bruce Fields" To: Alexander Viro Cc: Nick Piggin , linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] fs/dcache: allow __d_obtain_alias() to return unhashed dentries Message-ID: <20110118204509.GA10903@fieldses.org> References: <20101129193248.GA9897@fieldses.org> <20101203223326.GB28763@fieldses.org> <20101213051944.GA8688@amd> <20101214220102.GM24828@fieldses.org> <20101217180022.GB11515@fieldses.org> <20101218020118.GA3179@amd> <20101218161609.GA22150@fieldses.org> <20101227234641.GA22248@fieldses.org> Content-Type: text/plain; charset=utf-8 In-Reply-To: <20101227234641.GA22248@fieldses.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 An updated version attempting to take into account the new locking. (Nick, did I get this right?) --b. From: J. Bruce Fields Date: Fri, 17 Dec 2010 09:05:04 -0500 Subject: [PATCH] fs/dcache: allow __d_obtain_alias() to return unhashed dentries Without this patch, inodes are not promptly freed on last close of an unlinked file by an nfs client:        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 this, so it creates a new DCACHE_DISCONECTED dentry and returns that instead. - close: closes the existing filp, which is destroyed immediately by dput() since it's DCACHE_UNHASHED. - end of the compound: release the reference to the current filehandle, and dput() the new DCACHE_DISCONECTED dentry, which gets put on the unused list instead of being destroyed immediately. 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(-) diff --git a/fs/dcache.c b/fs/dcache.c index 9f493ee..2849258 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1521,6 +1521,28 @@ struct dentry * d_alloc_root(struct inode * root_inode) } EXPORT_SYMBOL(d_alloc_root); +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(alias); + return alias; +} + +static struct dentry * d_find_any_alias(struct inode *inode) +{ + struct dentry *de; + + spin_lock(&inode->i_lock); + de = __d_find_any_alias(inode); + spin_unlock(&inode->i_lock); + return de; +} + + /** * d_obtain_alias - find or allocate a dentry for a given inode * @inode: inode to allocate the dentry for @@ -1550,7 +1572,7 @@ 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; @@ -1563,7 +1585,7 @@ struct dentry *d_obtain_alias(struct inode *inode) spin_lock(&inode->i_lock); - res = __d_find_alias(inode, 0); + res = __d_find_any_alias(inode); if (res) { spin_unlock(&inode->i_lock); dput(tmp); -- 1.7.1