Re: [PATCH] PM / Hibernate: Fix memory corruption related to swap

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 3 Dec 2010 00:40:36 +0100
"Rafael J. Wysocki" <rjw@sisk.pl> wrote:

> From: Rafael J. Wysocki <rjw@sisk.pl>
> 
> There is a problem that swap pages allocated before the creation of
> a hibernation image can be released and used for storing the contents
> of different memory pages while the image is being saved.  Since the
> kernel stored in the image doesn't know of that, it causes memory
> corruption to occur after resume from hibernation, especially on
> systems with relatively small RAM that need to swap often.
> 
> This issue can be addressed by keeping the GFP_IOFS bits clear
> in gfp_allowed_mask during the entire hibernation, including the
> saving of the image, until the system is finally turned off or
> the hibernation is aborted.  Unfortunately, for this purpose
> it's necessary to rework the way in which the hibernate and
> suspend code manipulates gfp_allowed_mask.
> 
> This change is based on an earlier patch from Hugh Dickins.
> 
> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
> Reported-by: Ondrej Zary <linux@rainbow-software.org>
> Acked-by: Hugh Dickins <hughd@google.com>
> ---
> 
> Hi,
> 
> This patch is a fix for a regression and nasty memory corruption, so I'd like
> to push it to Linus for 2.6.37 if there are no objections.
> 

It looks OK to me for 2.6.37 but for 2.6.38 please let's make
everything here a 100% no-op for CONFIG_PM_SLEEP=n builds. 
Specifically the slight overhead in __alloc_pages_nodemask.

Because given the global nature of saved_gfp_mask and the unlocked way
in which it is accessed, this facility won't be at all useful for
anything other than suspend.