On Thu, Feb 24, 2011 at 03:58:37AM +0000, Al Viro wrote:

On Thu, Feb 24, 2011 at 11:28:57AM +0800, Ian Kent wrote:

quoted

Ha, I haven't even turned on my Ultrsparc 2 in months, it's only got an
old version of Solaris on it now anyway, ;)

U60, with lenny (and mainline kernel) on it.  Probably ought to upgrade
to squeeze one of those days...  It works, all right, but it's only 2-way,
so reproducing would probably be harder.  Plus the fun of building the tests
themselves on somewhat different userland...

Anyway, I wonder why you care about __d_lookup_rcu() and ->d_inode stability;
d_mountpoint() _is_ stable at that point (we hold vfsmount_lock) and you
don't seem to look at ->d_inode at all in RCU case.  Note that ->d_automount()
is never called in RCU case at all; nor is ->lookup() and friends, so you
really only have ->d_manage() to cope with, what with autofs4 having no
->d_revalidate() anymore.

FWIW, can we _ever_ get to __do_follow_link() with link->mnt != nd->path.mnt?
It's probably not what's happening here, or we would've stepped on another
BUG_ON(), but still it might be worth checking...

AFAICS, if we ever get there that way, we are fscked, so the check before
mntget() ought to replaced with BUG_ON(link->mnt != nd->path.mnt)...