[PATCH v3 18/19] nfs: use d_alloc_noblock() in silly-rename

[NeilBrown <neilb@ownmail.net>]

From: NeilBrown <neil@brown.name>

Rather than performing a normal lookup (which will be awkward with
future locking changes) use d_alloc_noblock() to find a dentry for an
unused name, and then open-code the rest of lookup_slow() to see if it
is free on the server.

Signed-off-by: NeilBrown <neil@brown.name>
---
 fs/nfs/unlink.c | 51 ++++++++++++++++++++++++++++++-------------------
 1 file changed, 31 insertions(+), 20 deletions(-)

diff --git a/fs/nfs/unlink.c b/fs/nfs/unlink.c
index 43ea897943c0..1ac9bd2a63b2 100644
--- a/fs/nfs/unlink.c
+++ b/fs/nfs/unlink.c
@@ -445,7 +445,7 @@ nfs_sillyrename(struct inode *dir, struct dentry *dentry)
 	static unsigned int sillycounter;
 	unsigned char silly[SILLYNAME_LEN + 1];
 	unsigned long long fileid;
-	struct dentry *sdentry;
+	struct dentry *sdentry, *old;
 	struct inode *inode = d_inode(dentry);
 	struct rpc_task *task;
 	int            error = -EBUSY;
@@ -462,26 +462,37 @@ nfs_sillyrename(struct inode *dir, struct dentry *dentry)
 
 	fileid = NFS_FILEID(d_inode(dentry));
 
-	sdentry = NULL;
-	do {
+newname:
+	sillycounter++;
+	scnprintf(silly, sizeof(silly),
+		  SILLYNAME_PREFIX "%0*llx%0*x",
+		  SILLYNAME_FILEID_LEN, fileid,
+		  SILLYNAME_COUNTER_LEN, sillycounter);
+
+	dfprintk(VFS, "NFS: trying to rename %pd to %s\n", dentry, silly);
+	sdentry = d_alloc_noblock(dentry->d_parent, &QSTR(silly));
+	if (sdentry == ERR_PTR(-EWOULDBLOCK))
+		/* Name currently being looked up */
+		goto newname;
+	/*
+	 * N.B. Better to return EBUSY here ... it could be
+	 * dangerous to delete the file while it's in use.
+	 */
+	if (IS_ERR(sdentry))
+		goto out;
+	if (d_is_positive(sdentry)) {
 		dput(sdentry);
-		sillycounter++;
-		scnprintf(silly, sizeof(silly),
-			  SILLYNAME_PREFIX "%0*llx%0*x",
-			  SILLYNAME_FILEID_LEN, fileid,
-			  SILLYNAME_COUNTER_LEN, sillycounter);
-
-		dfprintk(VFS, "NFS: trying to rename %pd to %s\n",
-				dentry, silly);
-
-		sdentry = lookup_noperm(&QSTR(silly), dentry->d_parent);
-		/*
-		 * N.B. Better to return EBUSY here ... it could be
-		 * dangerous to delete the file while it's in use.
-		 */
-		if (IS_ERR(sdentry))
-			goto out;
-	} while (d_inode(sdentry) != NULL); /* need negative lookup */
+		goto newname;
+	}
+	/* This name isn't known locally - check on server */
+	old = dir->i_op->lookup(dir, sdentry, 0);
+	d_lookup_done(sdentry);
+	if (old || d_is_positive(sdentry)) {
+		if (!IS_ERR(old))
+			dput(old);
+		dput(sdentry);
+		goto newname;
+	}
 
 	ihold(inode);
 
-- 
2.50.0.107.gf914562f5916.dirty