linux-kernel - [PATCH 1/2] mm, memcg: Fix corruption on 64-bit divisor in memory.high throttling

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Date:   Thu, 12 Mar 2020 18:02:54 +0000
From:   Chris Down <chris@...isdown.name>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Johannes Weiner <hannes@...xchg.org>, Tejun Heo <tj@...nel.org>,
        linux-mm@...ck.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: [PATCH 1/2] 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.

Fixes: 0e4b01df8659 ("mm, memcg: throttle allocators when failing reclaim over memory.high")
Reported-by: Johannes Weiner <hannes@...xchg.org>
Signed-off-by: Chris Down <chris@...isdown.name>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Tejun Heo <tj@...nel.org>
Cc: linux-mm@...ck.org
Cc: cgroups@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: kernel-team@...com
Cc: stable@...r.kernel.org # 5.4.x
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 63bb6a2aab81..a70206e516fe 100644
--- 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)
-- 
2.25.1