mm: fix free page check in zone_watermark_ok()
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 <5a6a90561cfaac16bd48243b2e87b9ad7d7fa747@ap.sony.com>
Tested-by: Aaditya Kumar <5a6a90561cfaac16bd48243b2e87b9ad7d7fa747@ap.sony.com>
Signed-off-by: Aaditya Kumar <5a6a90561cfaac16bd48243b2e87b9ad7d7fa747@ap.sony.com>
Signed-off-by: Minchan Kim <eee62f459f15dcddf87a8df69e8328e2a2562028@kernel.org>
Cc: KOSAKI Motohiro <70a1d3ef3e17a2bb0f09a1b2e6c86f607ed1d6d9@jp.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <634f508bd7c47cf0ee4126243675c3e598920fbc@jp.fujitsu.com>
Cc: Mel Gorman <39ea6a09710987173e32e37c86918024a0f441c1@suse.de>
Reviewed-by: Michal Hocko <829500b200af6c2a0eca4dfd5c388e6b8fbe8dc6@suse.cz>
Signed-off-by: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas