b=5210

b=5210
r=phil(actual patch)

A workaround for the crash in ll_unhash_aliases on 2.6.
The 2.6 lookup code is now lockless (thanks to the RCU machinations), which
allows it to race with the unhashing in ll_unhash_aliases. The 2.6 __d_drop
doesn't leave the list head ->pprev in a safe state, so the next pass through
this loop (which tries to re-hash it after we lose the dput race), would crash.
For the record, it looks like the kernel's own d_prune_aliases is broken in
the very same way, except that instead of crashing immediately, it just leaves
the d_hash pointers poisoned for someone else to crash on.