[PATCH] NFS: nfs4_lookup_revalidate need to report STALE inodes.

[NeilBrown <neilb@suse.de>]

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If an 'open' of a file in an NFSv4 filesystem finds that the dentry is
in cache, but the inode is stale (on the server), the dentry will not
be re-validated immediately and may cause ESTALE to be returned to
user-space.

For a non-create 'open', do_last() calls lookup_fast() and on success
will eventually call may_open() which calls into nfs_permission().
If nfs_permission() makes the ACCESS call to the server it will get
NFS4ERR_STALE, resulting in ESTALE from may_open() and thence from
do_last().
The retry-on-ESTALE in filename_lookup() will repeat exactly the same
process because nothing in this path will invalidate the dentry due to
the inode being stale, so the ESTALE will be returned.

lookup_fast() calls ->d_revalidate(), but for an OPEN on an NFSv4
filesystem, that will succeed for regular files:
	/* Let f_op->open() actually open (and revalidate) the file */

Unfortunately in the case of a STALE inode, f_op->open() never gets
called.  If we teach nfs4_lookup_revalidate() to report a failure on
NFS_STALE() inodes, then the dentry will be invalidated and a full
lookup will be attempted.  The ESTALE errors go away.


While I think this fix is correct, I'm not convinced that it is
sufficient, particularly if lookupcache=none.
The current code will fail an "open" is nfs_permission() fails,
without having performed a LOOKUP. i.e. it will use the cache.
nfs_lookup_revalidate will force a lookup before the permission check
if NFS_MOUNT_LOOKUP_CACHE_NONE, but nfs4_lookup_revalidate will not.


Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 4a3d4ef76127..4f7414afca27 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1563,6 +1563,8 @@ static int nfs4_lookup_revalidate(struct dentry *dentry, unsigned int flags)
 	/* We cannot do exclusive creation on a positive dentry */
 	if (flags & LOOKUP_EXCL)
 		goto no_open_dput;
+	if (NFS_STALE(inode))
+		goto no_open_dput;
 
 	/* Let f_op->open() actually open (and revalidate) the file */
 	ret = 1;

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