Messages in this thread | | | Date | Tue, 05 Jun 2012 07:41:52 -0300 | From | Cesar Eduardo Barros <> | Subject | frontswap: is frontswap_init called from swapoff safe? |
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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@cesarb.net cesar.barros@gmail.com
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