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

Commit 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.

Fixes: 0e4b01df8659 ("mm, memcg: throttle allocators when failing reclaim over memory.high")
Reported-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Chris Down <chris@chrisdown.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Nathan Chancellor <natechancellor@gmail.com>
Cc: <stable@vger.kernel.org>	[5.4.x+]
Link: http://lkml.kernel.org/r/80780887060514967d414b3cd91f9a316a16ab98.1584036142.git.chris@chrisdown.name
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 50492aa9d61b43b2b190c78fad73000c2abf19ef..6d276e1a3321020c6160c878f0159997f959fed4 100644 (file)
--- a/mm/memcontrol.c
+++ b/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)