32 bit overflow in mm/page_alloc.c

Binary package hint: linux-source-2.6.15

This patch has already been entered into latest -mm kernel and since it is trivial we would like to see it in dappers 2.6.15 if possible.

============

The patch titled

     setup_per_zone_pages_min() overflow fix

has been added to the -mm tree. Its filename is

     setup_per_zone_pages_min-overflow-fix.patch

See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this

From: Andrew Morton <email address hidden>

As pointed out in http://bugzilla.kernel.org/show_bug.cgi?id=6490, this
function can experience overflows on 32-bit machines, causing our response to
changed values of min_free_kbytes to go whacky.

Fixing it efficiently is all too hard, so fix it with 64-bit math instead.

Cc: Ake Sandgren <email address hidden>
Cc: Martin Bligh <email address hidden>
Signed-off-by: Andrew Morton <email address hidden>
---

 mm/page_alloc.c | 10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff -puN mm/page_alloc.c~setup_per_zone_pages_min-overflow-fix mm/page_alloc.c
--- 25/mm/page_alloc.c~setup_per_zone_pages_min-overflow-fix Tue May 9 13:56:14 2006
+++ 25-akpm/mm/page_alloc.c Tue May 9 13:57:46 2006
@@ -2635,9 +2635,11 @@ void setup_per_zone_pages_min(void)
        }

        for_each_zone(zone) {
- unsigned long tmp;
+ u64 tmp;
+
                spin_lock_irqsave(&zone->lru_lock, flags);
- tmp = (pages_min * zone->present_pages) / lowmem_pages;
+ tmp = (u64)pages_min * zone->present_pages;
+ do_div(tmp, lowmem_pages);
                if (is_highmem(zone)) {
                        /*
                         * __GFP_HIGH and PF_MEMALLOC allocations usually don't
@@ -2664,8 +2666,8 @@ void setup_per_zone_pages_min(void)
                        zone->pages_min = tmp;
                }

- zone->pages_low = zone->pages_min + tmp / 4;
- zone->pages_high = zone->pages_min + tmp / 2;
+ zone->pages_low = zone->pages_min + tmp >> 2;
+ zone->pages_high = zone->pages_min + tmp >> 1;
                spin_unlock_irqrestore(&zone->lru_lock, flags);
        }