linux-kernel - Re: sched: make struct task

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Message-ID: <d529c390-546e-a8a4-f475-c3ee41f97645@arm.com>
Date:   Mon, 23 Sep 2019 12:26:44 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Julia Lawall <julia.lawall@...6.fr>
Cc:     Markus Elfring <Markus.Elfring@....de>,
        Alexey Dobriyan <adobriyan@...il.com>, dm-devel@...hat.com,
        linux-block@...r.kernel.org, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: sched: make struct task_struct::state 32-bit

On 23/09/2019 11:34, Julia Lawall wrote:
>> // FIXME: current not recognized as task_struct*, fixhack with regexp
>> identifier current =~ "^current$";
> 
> Please don't do this.  Just use the word current.  It doesn't have to be a
> metavariable.  You will though get a warning about it.  To eliminate the
> warning, you can say symbol current;
> 

Didn't know about that way to get rid of the warning, thanks!

>> identifier task_state =~ "^TASK_";
> 
> Are there a lot of options?  You can also enumerate them in {}, ie
> 
> identifier task_state = {TASK_BLAH, TASK_BLAHBLAH};
> 

Around a dozen, can be enumerated easily and is indeed probably better than
a regexp.

>> identifier state_var;
>> position pos;
>> @@
>>
>> (
>>   p->state & state_var@pos
>> |
>>   current->state & state_var@pos
>> |
>>   p->state | state_var@pos
>> |
>>   current->state | state_var@pos
>> |
>>   p->state < state_var@pos
>> |
>>   current->state < state_var@pos
>> |
>>   p->state > state_var@pos
>> |
>>   current->state > state_var@pos
>> |
>>   state_var@pos = p->state
>> |
>>   state_var@pos = current->state
>> |
>>   p->state == state_var@pos
>> |
>>   current->state == state_var@pos
>> |
>>   p->state != state_var@pos
>> |
>>   current->state != state_var@pos
>> |
>> // FIXME: match functions that do something with state_var underneath?
>> // How to do recursive rules?
> 
> You want to look at the definitions of called functions?  Coccinelle
> doesn't really support that, but there are hackish ways to add that.  How
> many function calls would you expect have to be unrolled?
> 

I wouldn't expect more than a handful (~5). I suppose this has to do with
injecting some Python/Ocaml code? I have some examples bookmarked but
haven't gotten to stare at them long enough.

>>   set_current_state(state_var@pos)
>> |
>>   set_special_state(state_var@pos)
>> |
>>   signal_pending_state(state_var@pos, p)
>> |
>>   signal_pending_state(state_var@pos, current)
>> |
>>   state_var@pos & task_state
>> |
>>   state_var@pos | task_state
>> )
>>
>> // Fixup local variables
>> @depends on patch && state_access@
>> identifier state_var = state_access.state_var;
>> @@
>> (
>> - long
>> + int
>> |
>> - unsigned long
>> + unsigned int
>> )
>> state_var;
>>
>> // Fixup function parameters
>> @depends on patch && state_access@
>> identifier fn;
>> identifier state_var = state_access.state_var;
>> @@
>>
>> fn(...,
>> - long state_var
>> + int state_var
>> ,...)
>> {
>> 	...
>> }
>>
>> // FIXME: find a way to squash that with the above?
> 
> I think that you can make a disjunction on a function parameter
> 
> fn(...,
> (
> - T1 x1
> + T2 x2
> |
> - T3 x3
> + T4 x4
> )
> , ...) { ... }
> 

My attempt at this gives me "minus: parse error", which is why I went
with the split.

Something simple like this works:
---
virtual patch
virtual report

@@
identifier fn;
identifier p;
@@

fn(...,
- long
+ int
p
,...)
{
	...
}
---

but this doesn't:
---
virtual patch
virtual report

@@
identifier fn;
identifier p;
@@

fn(...,
(
- long p
+ int p
|
- unsigned long p
+ unsigned int p
)
,...)
{
	...
}
---

> julia
>