From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Cesar Eduardo Barros <cesarb@cesarb.net>
Cc: linux-kernel@vger.kernel.org,
Dan Magenheimer <dan.magenheimer@oracle.com>,
linux-mm@kvack.org
Subject: Re: frontswap: is frontswap_init called from swapoff safe?
Date: Wed, 6 Jun 2012 20:37:20 -0400 [thread overview]
Message-ID: <20120607003720.GI9472@phenom.dumpdata.com> (raw)
In-Reply-To: <4FCDE270.1020906@cesarb.net>
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.
>
> (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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WARNING: multiple messages have this Message-ID (diff)
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Cesar Eduardo Barros <cesarb@cesarb.net>
Cc: linux-kernel@vger.kernel.org,
Dan Magenheimer <dan.magenheimer@oracle.com>,
linux-mm@kvack.org
Subject: Re: frontswap: is frontswap_init called from swapoff safe?
Date: Wed, 6 Jun 2012 20:37:20 -0400 [thread overview]
Message-ID: <20120607003720.GI9472@phenom.dumpdata.com> (raw)
In-Reply-To: <4FCDE270.1020906@cesarb.net>
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.
>
> (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
next prev parent reply other threads:[~2012-06-07 0:44 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-05 10:41 frontswap: is frontswap_init called from swapoff safe? Cesar Eduardo Barros
2012-06-05 10:41 ` Cesar Eduardo Barros
2012-06-07 0:37 ` Konrad Rzeszutek Wilk [this message]
2012-06-07 0:37 ` Konrad Rzeszutek Wilk
2012-07-17 0:41 ` Cesar Eduardo Barros
2012-07-17 0:41 ` Cesar Eduardo Barros
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