[PATCH] NFS: nfs_lookup - don't hash dentry when optimising away the lookup

If the open intents tell us that a given lookup is going to result in a,
exclusive create, we currently optimize away the lookup call itself. The
reason is that the lookup would not be atomic with the create RPC call, so
why do it in the first place?

A problem occurs, however, if the VFS aborts the exclusive create operation
after the lookup, but before the call to create the file/directory: in this
case we will end up with a hashed negative dentry in the dcache that has
never been looked up.
Fix this by only actually hashing the dentry once the create operation has
been successfully completed.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index e7ffb4deb3e5f21973a0e165f229ddc98c7ff754..f86b9b4ea9d2310479192df91bcf3512f42732cd 100644 (file)
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -902,9 +902,15 @@ static struct dentry *nfs_lookup(struct inode *dir, struct dentry * dentry, stru
 
        lock_kernel();
 
-       /* If we're doing an exclusive create, optimize away the lookup */
-       if (nfs_is_exclusive_create(dir, nd))
-               goto no_entry;
+       /*
+        * If we're doing an exclusive create, optimize away the lookup
+        * but don't hash the dentry.
+        */
+       if (nfs_is_exclusive_create(dir, nd)) {
+               d_instantiate(dentry, NULL);
+               res = NULL;
+               goto out_unlock;
+       }
 
        error = NFS_PROTO(dir)->lookup(dir, &dentry->d_name, &fhandle, &fattr);
        if (error == -ENOENT)
@@ -1156,6 +1162,8 @@ int nfs_instantiate(struct dentry *dentry, struct nfs_fh *fhandle,
        if (IS_ERR(inode))
                goto out_err;
        d_instantiate(dentry, inode);
+       if (d_unhashed(dentry))
+               d_rehash(dentry);
        return 0;
 out_err:
        d_drop(dentry);