Re: [PATCH] mm/memcg: fix device private memcg accounting

[Andrew Morton]

On Fri, 9 Oct 2020 14:59:52 -0700 Ralph Campbell <rcampbell@xxxxxxxxxx> wrote:

> The code in mc_handle_swap_pte() checks for non_swap_entry() and returns
> NULL before checking is_device_private_entry() so device private pages
> are never handled.
> Fix this by checking for non_swap_entry() after handling device private
> swap PTEs.
> 
> Cc: stable@xxxxxxxxxxxxxxx

I was going to ask "what are the end-user visible effects of the bug". 
This is important information with a cc:stable.

> 
> I'm not sure exactly how to test this. I ran the HMM self tests but
> that is a minimal sanity check. I think moving the self test from one
> memory cgroup to another while it is running would exercise this patch.
> I'm looking at how the test could move itself to another group after
> migrating some anonymous memory to the test driver.
> 

But this makes me suspect the answer is "there aren't any that we know
of".  Are you sure a cc:stable is warranted?