Btrfs: only clear the need lookup flag after the dentry is setup

We can race with readdir and the RCU path walking stuff.  This is because we
clear the need lookup flag before actually instantiating the inode.  This will
lead the RCU path walk stuff to find a dentry it thinks is valid without a
d_inode attached.  So instead unhash the dentry when we first start the lookup,
and then clear the flag after we've instantiated the dentry so we're garunteed
to either try the slow lookup, or have the d_inode set properly.

Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 377e9bb0974fce95dc6e01f7c7dc52cc64f44e3d..b2d004ad66a0159042c38f96691c92bb0c31537e 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4018,7 +4018,8 @@ struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
                memcpy(&location, dentry->d_fsdata, sizeof(struct btrfs_key));
                kfree(dentry->d_fsdata);
                dentry->d_fsdata = NULL;
-               d_clear_need_lookup(dentry);
+               /* This thing is hashed, drop it for now */
+               d_drop(dentry);
        } else {
                ret = btrfs_inode_by_name(dir, dentry, &location);
        }
@@ -4085,7 +4086,15 @@ static void btrfs_dentry_release(struct dentry *dentry)
 static struct dentry *btrfs_lookup(struct inode *dir, struct dentry *dentry,
                                   struct nameidata *nd)
 {
-       return d_splice_alias(btrfs_lookup_dentry(dir, dentry), dentry);
+       struct dentry *ret;
+
+       ret = d_splice_alias(btrfs_lookup_dentry(dir, dentry), dentry);
+       if (unlikely(d_need_lookup(dentry))) {
+               spin_lock(&dentry->d_lock);
+               dentry->d_flags &= ~DCACHE_NEED_LOOKUP;
+               spin_unlock(&dentry->d_lock);
+       }
+       return ret;
 }
 
 unsigned char btrfs_filetype_table[] = {