Re: frontswap: is frontswap_init called from swapoff safe?

From: Cesar Eduardo Barros
Date: Mon Jul 16 2012 - 20:47:40 EST

Em 06-06-2012 21:37, Konrad Rzeszutek Wilk escreveu:
On Tue, Jun 05, 2012 at 07:41:52AM -0300, Cesar Eduardo Barros wrote:
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.

Let me look at this - can't do it this week - but will get back to you

Did you look at it already? (Just pinging in case you forgot.)

(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

Cesar Eduardo Barros

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