DCACHE_DISCONECTED dentries aren't always getting destroyed as soon as
I'd have expected in the NFSv4 case.
I'm not sure what the right fix is; any ideas? The below at least
demonstrates the problem.
--b.
commit bb125ffbe5fc3f80ac7a5b20f51cc542c175cd49
Author: J. Bruce Fields <bfields@xxxxxxxxxx>
Date: Thu Nov 11 19:22:00 2010 -0500
dput: free DCACHE_DISCONNECTED dentries sooner
DCACHE_DISCONECTED dentries are normally left around for the benefit of
future nfsd operations. But there's no point keeping them around once
the inode has been deleted.
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.
- 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.
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
diff --git a/fs/dcache.c b/fs/dcache.c
index 28fa7e5..5132f13 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -241,6 +241,10 @@ repeat:
/* Unreachable? Get rid of it */
if (d_unhashed(dentry))
goto kill_it;
+ if (dentry->d_flags & DCACHE_DISCONNECTED
+ && dentry->d_inode
+ && dentry->d_inode->i_nlink == 0)
+ goto kill_it;
if (list_empty(&dentry->d_lru)) {
dentry->d_flags |= DCACHE_REFERENCED;
dentry_lru_add(dentry);
--
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