linux-kernel - Re: [PATCH] sched: make struct task

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Date:   Wed, 4 Sep 2019 18:48:49 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     mingo@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
        linux-block@...r.kernel.org, dm-devel@...hat.com, axboe@...nel.dk,
        aarcange@...hat.com
Subject: Re: [PATCH] sched: make struct task_struct::state 32-bit

On 04/09/2019 13:07, Valentin Schneider wrote:
> [...]
> Baby steps...


There's something regarding coccinelle disjunctions that just can't grasp,
and this also fails to recognize "current" as being "struct task_struct*".

Once I fix these, it's "just" a matter of finding out how to write a rule
for layered calls (e.g. __kthread_bind() -> __kthread_bind_mask() ->
wait_task_inactive()), and we should be close to having something somewhat
usable.

---
virtual patch
virtual report

@state_access@
identifier func;
struct task_struct *p;
identifier state_var;
position fpos;
position epos;
@@

func(...)@fpos
{
	<...
(
  p->state & state_var@...s
|
  p->state | state_var@...s
|
  p->state < state_var@...s
|
  p->state > state_var@...s
|
  state_var@...s = p->state
// For some reason adding this disjunction gives us more matches, but causes
// some to go away :/
// |
//   p->state == state_var@...s
|
  p->state != state_var@...s
)
	...>
}

@depends on patch@
identifier fn = state_access.func;
identifier state_var = state_access.state_var;
@@

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

// Should be merged in the above but can't get disjunction to work
@depends on patch@
identifier fn = state_access.func;
identifier state_var = state_access.state_var;
@@

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

// Is it possible to match without semicolons? :/
@depends on patch@
identifier state_var = state_access.state_var;
expression E;
@@

(
- long state_var;
+ int state_var;
|
- long state_var = E;
+ int state_var = E;
)

@script:python depends on report@
fp << state_access.fpos;
ep << state_access.epos;
@@
cocci.print_main("Func at", fp)
cocci.print_main("Expr at", ep)