• Heiko Carstens's avatar
    mm/vmstat: fix overflow in mod_zone_page_state() · 6cdb18ad
    Heiko Carstens authored
    mod_zone_page_state() takes a "delta" integer argument.  delta contains
    the number of pages that should be added or subtracted from a struct
    zone's vm_stat field.
    
    If a zone is larger than 8TB this will cause overflows.  E.g.  for a
    zone with a size slightly larger than 8TB the line
    
        mod_zone_page_state(zone, NR_ALLOC_BATCH, zone->managed_pages);
    
    in mm/page_alloc.c:free_area_init_core() will result in a negative
    result for the NR_ALLOC_BATCH entry within the zone's vm_stat, since 8TB
    contain 0x8xxxxxxx pages which will be sign extended to a negative
    value.
    
    Fix this by changing the delta argument to long type.
    
    This could fix an early boot problem seen on s390, where we have a 9TB
    system with only one node.  ZONE_DMA contains 2GB and ZONE_NORMAL the
    rest.  The system is trying to allocate a GFP_DMA page but ZONE_DMA is
    completely empty, so it tries to reclaim pages in an endless loop.
    
    This was seen on a heavily patched 3.10 kernel.  One possible
    explaination seem to be the overflows caused by mod_zone_page_state().
    Unfortunately I did not have the chance to verify that this patch
    actually fixes the problem, since I don't have access to the system
    right now.  However the overflow problem does exist anyway.
    
    Given the description that a system with slightly less than 8TB does
    work, this seems to be a candidate for the observed problem.
    Signed-off-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
    Cc: Christoph Lameter <cl@linux.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    6cdb18ad
vmstat.c 41.3 KB