I was looking at the swapfile.c parts of the recently-merged frontswap,
and noticed that frontswap_init can be called from swapoff when
try_to_unuse fails.
This looks odd to me. Whether it is safe or not depends on what
frontswap_ops.init does, but the comment for __frontswap_init ("Called
when a swap device is swapon'd") and the function name itself seem to
imply it should be called only for swapon, not when relinking the
swap_info after a failed swapoff.
In particular, if frontswap_ops.init assumes the swap map is empty, it
would break, since as far as I know when try_to_unuse fails there are
still pages in the swap.
(By the way, the comment above enable_swap_info at sys_swapoff needs to
be updated to also explain why reading p->frontswap_map outside the lock
is safe at that point, like it does for p->prio and p->swap_map.)
--
Cesar Eduardo Barros
cesarb@xxxxxxxxxx
cesar.barros@xxxxxxxxx
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