[Bug 44782] 32 bit overflow in mm/page_alloc.c

[ake sandgren]

Public bug reported:

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 <akpm at osdl.org>

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 <ake.sandgren at hpc2n.umu.se>
Cc: Martin Bligh <mbligh at google.com>
Signed-off-by: Andrew Morton <akpm at osdl.org>
---

 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);
        }

** Affects: linux-source-2.6.15 (Ubuntu)
       Severity: Normal
       Priority: (none set)
         Status: Unconfirmed

-- 
32 bit overflow in mm/page_alloc.c
https://launchpad.net/bugs/44782