fuse: always revalidate if exclusive create

Failure to do so may result in EEXIST even if the file only exists in the
cache and not in the filesystem.

The atomic nature of O_EXCL mandates that the cached state should be
ignored and existence verified anew.

Reported-by: Ken Schalk <kschalk@nvidia.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/dir.c

@@ -205,7 +205,7 @@ static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags)
 	if (inode && is_bad_inode(inode))
 		goto invalid;
 	else if (time_before64(fuse_dentry_time(entry), get_jiffies_64()) ||
-		 (flags & LOOKUP_REVAL)) {
+		 (flags & (LOOKUP_EXCL | LOOKUP_REVAL))) {
 		struct fuse_entry_out outarg;
 		FUSE_ARGS(args);
 		struct fuse_forget_link *forget;