Re: [PATCH 08/23] membarrier: Remove redundant clear of mm->membarrier_state in exec_mmap()

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

----- On Jan 8, 2022, at 11:43 AM, Andy Lutomirski luto@kernel.org wrote:

> exec_mmap() supplies a brand-new mm from mm_alloc(), and membarrier_state
> is already 0.  There's no need to clear it again.

Then I suspect we might want to tweak the comment just above the memory barrier ?

        /*
         * Issue a memory barrier before clearing membarrier_state to
         * guarantee that no memory access prior to exec is reordered after
         * clearing this state.
         */

Is that barrier still needed ?

Thanks,

Mathieu

> 
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> kernel/sched/membarrier.c | 1 -
> 1 file changed, 1 deletion(-)
> 
> diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
> index eb73eeaedc7d..c38014c2ed66 100644
> --- a/kernel/sched/membarrier.c
> +++ b/kernel/sched/membarrier.c
> @@ -285,7 +285,6 @@ void membarrier_exec_mmap(struct mm_struct *mm)
> 	 * clearing this state.
> 	 */
> 	smp_mb();
> -	atomic_set(&mm->membarrier_state, 0);
> 	/*
> 	 * Keep the runqueue membarrier_state in sync with this mm
> 	 * membarrier_state.
> --
> 2.33.1

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