On Thu, Jun 27, 2019 at 12:09:29PM -0700, Dan Williams wrote:
> > This bug feels like we failed to unlock, or unlocked the wrong entry
> > and this hunk in the bisected commit looks suspect to me. Why do we
> > still need to drop the lock now that the radix_tree_preload() calls
> > are gone?
>
> Nevermind, unmapp_mapping_pages() takes a sleeping lock, but then I
> wonder why we don't restart the lookup like the old implementation.
We have the entry locked:
/*
* Make sure 'entry' remains valid while we drop
* the i_pages lock.
*/
dax_lock_entry(xas, entry);
/*
* Besides huge zero pages the only other thing that gets
* downgraded are empty entries which don't need to be
* unmapped.
*/
if (dax_is_zero_entry(entry)) {
xas_unlock_irq(xas);
unmap_mapping_pages(mapping,
xas->xa_index & ~PG_PMD_COLOUR,
PG_PMD_NR, false);
xas_reset(xas);
xas_lock_irq(xas);
}
If something can remove a locked entry, then that would seem like the
real bug. Might be worth inserting a lookup there to make sure that it
hasn't happened, I suppose?
