d_walk() might skip too much
Al Viro [Fri, 29 May 2015 03:09:19 +0000 (23:09 -0400)]
commit 2159184ea01e4ae7d15f2017e296d4bc82d5aeb0 upstream.

when we find that a child has died while we'd been trying to ascend,
we should go into the first live sibling itself, rather than its sibling.

Off-by-one in question had been introduced in "deal with deadlock in
d_walk()" and the fix needs to be backported to all branches this one
has been backported to.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/dcache.c

index efa4602..e280092 100644 (file)
@@ -1179,13 +1179,13 @@ ascend:
                /* might go back up the wrong parent if we have had a rename. */
                if (!locked && read_seqretry(&rename_lock, seq))
                        goto rename_retry;
-               next = child->d_child.next;
-               while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED)) {
+               /* go into the first sibling still alive */
+               do {
+                       next = child->d_child.next;
                        if (next == &this_parent->d_subdirs)
                                goto ascend;
                        child = list_entry(next, struct dentry, d_child);
-                       next = next->next;
-               }
+               } while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
                rcu_read_unlock();
                goto resume;
        }