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Commit d6bbbd29 authored by Raymond Jennings's avatar Raymond Jennings Committed by Linus Torvalds
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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.

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 64G
# 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

[akpm@linux-foundation.org: fix warning]
Signed-off-by: default avatarRaymond Jennings <shentino@gmail.com>
Acked-by: default avatarValdis Kletnieks <valdis.kletnieks@vt.edu>
Reviewed-by: default avatarRik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ec9bed9d

mm/swapfile.c

+10 −2
Original line number Diff line number Diff line
@@ -1926,6 +1926,7 @@ static unsigned long read_swap_header(struct swap_info_struct *p, 
	int i;

	unsigned long maxpages;

	unsigned long swapfilepages;

	unsigned long last_page;



	if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {

		printk(KERN_ERR "Unable to find swap-space signature\n");
@@ -1968,8 +1969,15 @@ 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) {

		maxpages = swap_header->info.last_page + 1;

	last_page = swap_header->info.last_page;

	if (last_page > maxpages) {

		printk(KERN_WARNING

			"Truncating oversized swap area, only using %luk out of %luk\n",

			maxpages << (PAGE_SHIFT - 10),

			last_page << (PAGE_SHIFT - 10));

	}

	if (maxpages > last_page) {

		maxpages = last_page + 1;

		/* p->max is an unsigned int: don't overflow it */

		if ((unsigned int)maxpages == 0)

			maxpages = UINT_MAX;