mm, memcg: fix corruption on 64-bit divisor in memory.high throttling

Commit 0e4b01d 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.

Fixes: 0e4b01d ("mm, memcg: throttle allocators when failing reclaim over memory.high")
Reported-by: Johannes Weiner <[email protected]>
Signed-off-by: Chris Down <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: <[email protected]>	[5.4.x+]
Link: http://lkml.kernel.org/r/80780887060514967d414b3cd91f9a316a16ab98.1584036142.git.chris@chrisdown.name
Signed-off-by: Linus Torvalds <[email protected]>

Author: cdown

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)