[PATCH] autofs4: fix race in unhashed dentry code

Commit f50b6f8691cae2e0064c499dd3ef3f31142987f0 introduced a race in
autofs4 between autofs_lookup_unhashed() and autofs_dentry_release().

autofs_dentry_release() ends up clearing the ->dentry and ->inode members
of autofs_info before removing it from the rehash list. The list is
protected by the rehash lock in both functions, but since
autofs_dentry_release() starts tearing the autofs_info struct down before
removing it from the list, autofs_lookup_unhashed() can get a autofs_info
with a NULL dentry.

This patch moves the clearing of ->dentry and ->inode after the removal
from the rehash list.

Signed-off-by: Jeff Mahoney <[e-mail]>
Acked-by: Ian Kent <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/autofs4/root.c

···
 	if (inf) {
 		struct autofs_sb_info *sbi = autofs4_sbi(de->d_sb);
 
-		inf->dentry = NULL;
-		inf->inode = NULL;
-
 		if (sbi) {
 			spin_lock(&sbi->rehash_lock);
 			if (!list_empty(&inf->rehash))
 				list_del(&inf->rehash);
 			spin_unlock(&sbi->rehash_lock);
 		}
+
+		inf->dentry = NULL;
+		inf->inode = NULL;
 
 		autofs4_free_ino(inf);
 	}