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

[Johannes Weiner]

On Thu, Mar 12, 2020 at 06:02:54PM +0000, Chris Down wrote:
> 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@xxxxxxxxxxx>
> Signed-off-by: Chris Down <chris@xxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: cgroups@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: kernel-team@xxxxxx
> Cc: stable@xxxxxxxxxxxxxxx # 5.4.x

div_u64 versus div64_u64 is really a handgrenade. We just fixed a
bunch of those in psi as well.

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>