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

Raymond Jennings
2013-07-07T20:56:51Z

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@gmail.com>
> > Acked-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
>
> Reviewed-by: Rik van Riel <riel@redhat.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
> >
> >
>
>