Commit d6bbbd29 authored Sep 11, 2013 by Raymond Jennings Committed by Linus Torvalds Sep 11, 2013

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: Raymond Jennings <shentino@gmail.com>
Acked-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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;

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