From 2cfed0752808625d30aca7fc9f383af386fd8a13 Mon Sep 17 00:00:00 2001 From: Minchan Kim Date: Tue, 31 Jul 2012 16:43:53 -0700 Subject: [PATCH] mm: fix free page check in zone_watermark_ok() __zone_watermark_ok currently compares free_pages which is a signed type with z->lowmem_reserve[classzone_idx] which is unsigned which might lead to sign overflow if free_pages doesn't satisfy the given order (or it came as negative already) and then we rely on the following order loop to fix it (which doesn't work for order-0). Let's fix the type conversion and do not rely on the given value of free_pages or follow up fixups. This patch fixes it because "memory-hotplug: fix kswapd looping forever problem" depends on this. As benefit of this patch, it doesn't rely on the loop to exit __zone_watermark_ok in case of high order check and make the first test effective.(ie, if (free_pages <= min + lowmem_reserve)) Aaditya reported this problem when he test my hotplug patch. Reported-off-by: Aaditya Kumar Tested-by: Aaditya Kumar Signed-off-by: Aaditya Kumar Signed-off-by: Minchan Kim Cc: KOSAKI Motohiro Cc: KAMEZAWA Hiroyuki Cc: Mel Gorman Reviewed-by: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_alloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 228194728cc..2e663599355 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1595,6 +1595,7 @@ static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark, { /* free_pages my go negative - that's OK */ long min = mark; + long lowmem_reserve = z->lowmem_reserve[classzone_idx]; int o; free_pages -= (1 << order) - 1; @@ -1603,7 +1604,7 @@ static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark, if (alloc_flags & ALLOC_HARDER) min -= min / 4; - if (free_pages <= min + z->lowmem_reserve[classzone_idx]) + if (free_pages <= min + lowmem_reserve) return false; for (o = 0; o < order; o++) { /* At the next order, this order's pages become unavailable */ -- 2.20.1