linux-kernel - Re: [PATCH v2] swap: warn when a swap area overflows the maximum size

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Date:	Sun, 07 Jul 2013 13:56:45 -0700
From:	Raymond Jennings <shentino@...il.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Valdis Kletnieks <valdis.kletnieks@...edu>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] swap: warn when a swap area overflows the maximum
 size

Screwed up and didn't attach my fixed test log to the second version.

See below.

On Sun, 2013-07-07 at 15:31 -0400, Rik van Riel wrote:
> On 07/07/2013 03:13 PM, Raymond Jennings wrote:
> > Turned the comparison around for clarity of "bigger than"
> >
> > No semantic changes, if it still compiles it should do the same thing so
> > I've omitted the testing this time.  Will be happy to retest if required
> > but I'm on an atom 330 and kernel rebuilds are a nightmare.
> 
> Added CC: Andrew Morton, since this should probably go into -mm :)
> 
> > ----
> >
> > swap: warn when a swap area overflows the maximum size
> >
> > It is possible to swapon a swap area that is too big for the pte width
> > to handle.
> >
> > Presently this failure happens silently.
> >
> > Instead, emit a diagnostic to warn the user.
> >
> > Signed-off-by: Raymond Jennings <shentino@...il.com>
> > Acked-by: Valdis Kletnieks <valdis.kletnieks@...edu>
> 
> Reviewed-by: Rik van Riel <riel@...hat.com>
> 
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index 36af6ee..5a4ce53 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -1953,6 +1953,12 @@ static unsigned long read_swap_header(struct
> > swap_info_struct *p,
> >           */
> >          maxpages = swp_offset(pte_to_swp_entry(
> >                          swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
> > +       if (swap_header->info.last_page > maxpages) {
> > +               printk(KERN_WARNING
> > +                      "Truncating oversized swap area, only using %luk
> > out of %luk
> > \n",
> > +                      maxpages << (PAGE_SHIFT - 10),
> > +                      swap_header->info.last_page << (PAGE_SHIFT -
> > 10));
> > +       }
> >          if (maxpages > swap_header->info.last_page) {
> >                  maxpages = swap_header->info.last_page + 1;
> >                  /* p->max is an unsigned int: don't overflow it */
> >
> > ----
> >
> > Testing results, root prompt commands and kernel log messages:
> >
> > # lvresize /dev/system/swap --size 16G
> > # mkswap /dev/system/swap
> > # swapon /dev/system/swap
> >
> > Jul  7 04:27:22 warfang kernel: Adding 16777212k swap
> > on /dev/mapper/system-swap.  Priority:-1 extents:1 across:16777212k
> >
> > # lvresize /dev/system/swap --size 16G

On Sun, 2013-07-07 at 04:52 -0700, Raymond Jennings wrote:
> # lvresize /dev/system/swap --size 16G

Typo in the second test.

The first line should read:

# lvresize /dev/system/swap --size 64G

First ever serious patch, got excited and burned the copypasta.

> # mkswap /dev/system/swap
> # swapon /dev/system/swap

> > # mkswap /dev/system/swap
> > # swapon /dev/system/swap
> >
> > Jul  7 04:27:22 warfang kernel: Truncating oversized swap area, only
> > using 33554432k out of 67108860k
> > Jul  7 04:27:22 warfang kernel: Adding 33554428k swap
> > on /dev/mapper/system-swap.  Priority:-1 extents:1 across:33554428k
> >
> >
> 
> 


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