linux-kernel - Re: [PATCH 1/3] sched: fix exit

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Date:   Tue, 20 Oct 2020 10:59:58 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Boqun Feng <boqun.feng@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Will Deacon <will@...nel.org>, paulmck <paulmck@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH 1/3] sched: fix exit_mm vs membarrier (v4)

----- On Oct 20, 2020, at 10:36 AM, Peter Zijlstra peterz@...radead.org wrote:

> On Tue, Oct 20, 2020 at 09:47:13AM -0400, Mathieu Desnoyers wrote:
>> +void membarrier_update_current_mm(struct mm_struct *next_mm)
>> +{
>> +	struct rq *rq = this_rq();
>> +	int membarrier_state = 0;
>> +
>> +	if (next_mm)
>> +		membarrier_state = atomic_read(&next_mm->membarrier_state);
>> +	if (READ_ONCE(rq->membarrier_state) == membarrier_state)
>> +		return;
>> +	WRITE_ONCE(rq->membarrier_state, membarrier_state);
>> +}
> 
> This is suspisioucly similar to membarrier_switch_mm().
> 
> Would something like so make sense?

Very much yes. Do you want me to re-send the series, or you
want to fold this in as you merge it ?

Thanks,

Mathieu

> 
> ---
> --- a/kernel/sched/membarrier.c
> +++ b/kernel/sched/membarrier.c
> @@ -206,14 +206,7 @@ void membarrier_exec_mmap(struct mm_stru
> 
> void membarrier_update_current_mm(struct mm_struct *next_mm)
> {
> -	struct rq *rq = this_rq();
> -	int membarrier_state = 0;
> -
> -	if (next_mm)
> -		membarrier_state = atomic_read(&next_mm->membarrier_state);
> -	if (READ_ONCE(rq->membarrier_state) == membarrier_state)
> -		return;
> -	WRITE_ONCE(rq->membarrier_state, membarrier_state);
> +	membarrier_switch_mm(this_rq(), NULL, next_mm);
> }
> 
> static int membarrier_global_expedited(void)
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index d2621155393c..3d589c2ffd28 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2645,12 +2645,14 @@ static inline void membarrier_switch_mm(struct rq *rq,
> 					struct mm_struct *prev_mm,
> 					struct mm_struct *next_mm)
> {
> -	int membarrier_state;
> +	int membarrier_state = 0;
> 
> 	if (prev_mm == next_mm)
> 		return;
> 
> -	membarrier_state = atomic_read(&next_mm->membarrier_state);
> +	if (next_mm)
> +		membarrier_state = atomic_read(&next_mm->membarrier_state);
> +
> 	if (READ_ONCE(rq->membarrier_state) == membarrier_state)
>  		return;

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com