[patch 04/10] mm, memcg: fix corruption on 64-bit divisor in memory.high throttling

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From: Chris Down <chris@xxxxxxxxxxxxxx>
Subject: mm, memcg: fix corruption on 64-bit divisor in memory.high throttling

0e4b01df8659 had a bunch of fixups to use the right division method. 
However, it seems that after all that it still wasn't right -- div_u64
takes a 32-bit divisor.

The headroom is still large (2^32 pages), so on mundane systems you won't
hit this, but this should definitely be fixed.

Link: http://lkml.kernel.org/r/80780887060514967d414b3cd91f9a316a16ab98.1584036142.git.chris@xxxxxxxxxxxxxx
Fixes: 0e4b01df8659 ("mm, memcg: throttle allocators when failing reclaim over memory.high")
Signed-off-by: Chris Down <chris@xxxxxxxxxxxxxx>
Reported-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Nathan Chancellor <natechancellor@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>	[5.4.x+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/memcontrol.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/memcontrol.c~mm-memcg-fix-corruption-on-64-bit-divisor-in-memoryhigh-throttling
+++ a/mm/memcontrol.c
@@ -2339,7 +2339,7 @@ void mem_cgroup_handle_over_high(void)
 	 */
 	clamped_high = max(high, 1UL);
 
-	overage = div_u64((u64)(usage - high) << MEMCG_DELAY_PRECISION_SHIFT,
+	overage = div64_u64((u64)(usage - high) << MEMCG_DELAY_PRECISION_SHIFT,
 			  clamped_high);
 
 	penalty_jiffies = ((u64)overage * overage * HZ)
_



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