linux-kernel - Re: frontswap: is frontswap_init called from swapoff safe?

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Message-ID: <5004B49C.6010708@cesarb.net>
Date:	Mon, 16 Jul 2012 21:41:00 -0300
From:	Cesar Eduardo Barros <cesarb@...arb.net>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	linux-kernel@...r.kernel.org,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	linux-mm@...ck.org
Subject: Re: frontswap: is frontswap_init called from swapoff safe?

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.
>
> <nods>
>>
>> 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
> shortly.

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
>> p->swap_map.)

-- 
Cesar Eduardo Barros
cesarb@...arb.net
cesar.barros@...il.com


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