Re: [PATCH 2/2] md: Change active_io to percpu

[Ming Lei <ming.lei@redhat.com>]

On Sat, Jan 21, 2023 at 09:39:37AM +0800, Xiao Ni wrote:
> Now the type of active_io is atomic. It's used to count how many ios are
> in the submitting process and it's added and decreased very time. But it
> only needs to check if it's zero when suspending the raid. So we can
> switch atomic to percpu to improve the performance.
> 
> After switching active_io to percpu type, we use the state of active_io
> to judge if the raid device is suspended. And we don't need to wake up
> ->sb_wait in md_handle_request anymore. It's done in the callback function
> which is registered when initing active_io. The argument mddev->suspended
> is only used to count how many users are trying to set raid to suspend
> state.
> 
> Signed-off-by: Xiao Ni <xni@redhat.com>
> ---
>  drivers/md/md.c | 40 ++++++++++++++++++++++++----------------
>  drivers/md/md.h |  2 +-
>  2 files changed, 25 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index d3627aad981a..04c067cf2f53 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -382,10 +382,7 @@ static DEFINE_SPINLOCK(all_mddevs_lock);
>  
>  static bool is_md_suspended(struct mddev *mddev)
>  {
> -	if (mddev->suspended)
> -		return true;
> -	else
> -		return false;
> +	return percpu_ref_is_dying(&mddev->active_io);
>  }
>  /* Rather than calling directly into the personality make_request function,
>   * IO requests come here first so that we can check if the device is
> @@ -412,7 +409,6 @@ static bool is_suspended(struct mddev *mddev, struct bio *bio)
>  void md_handle_request(struct mddev *mddev, struct bio *bio)
>  {
>  check_suspended:
> -	rcu_read_lock();
>  	if (is_suspended(mddev, bio)) {
>  		DEFINE_WAIT(__wait);
>  		/* Bail out if REQ_NOWAIT is set for the bio */
> @@ -432,17 +428,15 @@ void md_handle_request(struct mddev *mddev, struct bio *bio)
>  		}
>  		finish_wait(&mddev->sb_wait, &__wait);
>  	}

Hi Xiao,

All rcu_read_unlock/rcu_read_lock should be removed from the above
branch, and that could cause the ktest robot warning.

Thanks,
Ming