Re: [ELISA Development Process WG] [PATCH] mm: vmscan: provide a change to the development-process group

> -----Original Message-----
> From: [email protected] <development-
> [email protected]> On Behalf Of Lukas Bulwahn
> Sent: Thursday, September 17, 2020 10:44 AM
> To: [email protected]
> Cc: [email protected]; Lukas Bulwahn
> <[email protected]>
> Subject: [ELISA Development Process WG] [PATCH] mm: vmscan: provide a
> change to the development-process group
> 
> I think this change is needed for safety, whatever that might mean to you.
> 
> I am unqualified to really make a change here, as I have no clue what this
> code does, nor what my change does, but sure, the testing and verification
> reference process can now point out the required next steps in the
> reference process to test this code and code change.
> 
> Good luck :)
> 
> Not intended for distribution to the general kernel mailing lists.
> 
> Signed-off-by: Lukas Bulwahn <[email protected]>
> ---
> I would like to submit such a patch, what do I need to do according to
> the expected testing and verification recommendations for safety-related
> systems?

Probably the problem is not just limited to submitting patches, but I think it
is a good starting point.

> 
> Please help me. What do I need to compile, what test do I need to run,
> which verification tool do I need to employ for this change?

Right. I have tried to reformulate the problem as "ok I am looking at or I am
trying to change one or more code lines, so I would like to understand if such
code lines are tested today and how".
Right now if we had a s maintained structural coverage report we could tell
if the impacted code lines are covered and by which tests...I could not find it
so I guess that so far we are missing it....am I wrong?

As next step I went to look at the function wrapping the impacted code line
that in this case is kswapd. I could not find it tested in the Kunit framework.

As next steps then I would run the available tests in
https://elixir.bootlin.com/linux/latest/source/tools/testing/selftests
in conjunction with GCOV trying to figure out if that line is covered already
somehow.

There are probably smarter, better, faster ways to elaborate on this...so
here I just put down what I would do in order to figure this out...

Gab


> 
> Or even more basic: where would I even find that information?
> 
>  mm/vmscan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 980155e257bf..aef8060efa8f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3893,7 +3893,7 @@ static int kswapd(void *p)
>  					highest_zoneidx);
> 
>  		/* Read the new order and highest_zoneidx */
> -		alloc_order = reclaim_order = READ_ONCE(pgdat-
> >kswapd_order);
> +		alloc_order = READ_ONCE(pgdat->kswapd_order);
>  		highest_zoneidx = kswapd_highest_zoneidx(pgdat,
>  							highest_zoneidx);
>  		WRITE_ONCE(pgdat->kswapd_order, 0);
> --
> 2.17.1
> 
> 
> 
> 
> 

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