From: J. Bruce Fields <bfields@xxxxxxxxxx>
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. ÂOn-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. ÂThe 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.
Acked-by: Nick Piggin <npiggin@xxxxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
---
fs/dcache.c | 26 ++++++++++++++++++++++++--
1 files changed, 24 insertions(+), 2 deletions(-)
On Mon, Dec 20, 2010 at 01:53:10AM +1100, Nick Piggin wrote:
> On Sun, Dec 19, 2010 at 3:16 AM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
> > On Sat, Dec 18, 2010 at 01:01:18PM +1100, Nick Piggin wrote:
> >> 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.
>
> OK that makes a lot more sense :)
Thanks very much for your help!--b.
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);
--
1.7.3.4
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