autofs: fix lockref lookup

commit 6b6751f7feba68d8f5c72b72cc69a1c5a625529c upstream.

autofs needs to be able to see private data dentry flags for its dentrys
that are being created but not yet hashed and for its dentrys that have
been rmdir()ed but not yet freed.  It needs to do this so it can block
processes in these states until a status has been returned to indicate
the given operation is complete.

It does this by keeping two lists, active and expring, of dentrys in
this state and uses ->d_release() to keep them stable while it checks
the reference count to determine if they should be used.

But with the recent lockref changes dentrys being freed sometimes don't
transition to a reference count of 0 before being freed so autofs can
occassionally use a dentry that is invalid which can lead to a panic.

Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index 92ef341ba0cf35c1bd1b5f001b9b39068979f6ff..2a69bde8c61d03e50c021406eb42abfe2af95cc1 100644 (file)
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -179,7 +179,7 @@ static struct dentry *autofs4_lookup_active(struct dentry *dentry)
                spin_lock(&active->d_lock);
 
                /* Already gone? */
-               if (!d_count(active))
+               if ((int) d_count(active) <= 0)
                        goto next;
 
                qstr = &active->d_name;
@@ -230,7 +230,7 @@ static struct dentry *autofs4_lookup_expiring(struct dentry *dentry)
 
                spin_lock(&expiring->d_lock);
 
-               /* Bad luck, we've already been dentry_iput */
+               /* We've already been dentry_iput or unlinked */
                if (!expiring->d_inode)
                        goto next;