2013-07-07 11:44:17

by Raymond Jennings

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

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 <[email protected]>
Acked-by: Valdis Kletnieks <[email protected]>

----

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 (maxpages < swap_header->info.last_page) {
+ 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
# 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

2013-07-07 11:53:05

by Raymond Jennings

Subject: [PATCH] swap: warn when a swap area overflows the maximum size (resent)

Silly me, wrong email address

On Sun, 2013-07-07 at 04:44 -0700, Raymond Jennings wrote:
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 <[email protected]>
Acked-by: Valdis Kletnieks <[email protected]>

----

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 (maxpages < swap_header->info.last_page) {
+ 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
# 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

2013-07-07 12:01:31

by Raymond Jennings

Subject: Re: [PATCH] swap: warn when a swap area overflows the maximum size (resent)

...I hate you gmail...

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
>
> 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

2013-07-07 19:13:46

by Raymond Jennings

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

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.

----

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 <[email protected]>
Acked-by: Valdis Kletnieks <[email protected]>

----

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
# 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

2013-07-07 19:31:42

by Rik van Riel

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

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 <[email protected]>
> Acked-by: Valdis Kletnieks <[email protected]>

Reviewed-by: Rik van Riel <[email protected]>

> 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
> # 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
>
>


--
All rights reversed

2013-07-07 20:56:51

by Raymond Jennings

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 <[email protected]>
> > Acked-by: Valdis Kletnieks <[email protected]>
>
> Reviewed-by: Rik van Riel <[email protected]>
>
> > 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
> >
> >
>
>