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 <aaditya.kumar@ap.sony.com> Tested-by: Aaditya Kumar <aaditya.kumar@ap.sony.com> Signed-off-by: Aaditya Kumar <aaditya.kumar@ap.sony.com> Signed-off-by: Minchan Kim <minchan@kernel.org> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Mel Gorman <mgorman@suse.de> Reviewed-by: Michal Hocko <mhocko@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -1595,6 +1595,7 @@ static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark,
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{
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/* free_pages my go negative - that's OK */
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long min = mark;
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long lowmem_reserve = z->lowmem_reserve[classzone_idx];
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int o;
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free_pages -= (1 << order) - 1;
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@ -1603,7 +1604,7 @@ static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark,
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if (alloc_flags & ALLOC_HARDER)
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min -= min / 4;
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if (free_pages <= min + z->lowmem_reserve[classzone_idx])
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if (free_pages <= min + lowmem_reserve)
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return false;
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for (o = 0; o < order; o++) {
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/* At the next order, this order's pages become unavailable */
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