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

[Rafael J. Wysocki]

On Friday, December 03, 2010, Andrew Morton wrote:
> On Fri, 3 Dec 2010 00:40:36 +0100
> "Rafael J. Wysocki" <rjw@xxxxxxx> wrote:
> 
> > From: Rafael J. Wysocki <rjw@xxxxxxx>
> > 
> > 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@xxxxxxx>
> > Reported-by: Ondrej Zary <linux@xxxxxxxxxxxxxxxxxxxx>
> > Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
> > ---
> > 
> > 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.

OK, I'll take care of it.

> 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.

Right.
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