Re: [PATCH 07/14] md: move bitmap_destroy before __md_stop

[Shaohua Li <shli@kernel.org>]

On Fri, Feb 24, 2017 at 11:15:17AM +0800, Guoqing Jiang wrote:
> Since we have switched to sync way to handle METADATA_UPDATED
> msg for md-cluster, then process_metadata_update is depended
> on mddev->thread->wqueue.
> 
> With the new change, clustered raid could possible hang if
> array received a METADATA_UPDATED msg after array unregistered
> mddev->thread, so we need to stop clustered raid earlier
> than before.
> 
> And this change should be safe for non-clustered raid since
> all writes are stopped before the destroy. Also in md_run,
> we activate the personality (pers->run()) before activating
> the bitmap (bitmap_create()). So it is pleasingly symmetric
> to stop the bitmap (bitmap_destroy()) before stopping the
> personality (__md_stop() calls pers->free()).

There is no patch 6. So I can't judge the purpose of the patch.

The patch changed behaviors. We only destroy bitmap with mode == 0, now we do it
even for mode == 2. Please specify why it's safe. The __md_stop will wait for
behind writes for example only with bitmap set, but the patch makes us not do
the wait.

> Reviewed-by: NeilBrown <neilb@suse.com>
> Signed-off-by: Guoqing Jiang <gqjiang@suse.com>
> ---
>  drivers/md/md.c | 28 +++++++++++++++-------------
>  1 file changed, 15 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 6e910d99c9c1..7bcc757386e1 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -5582,8 +5582,8 @@ void md_stop(struct mddev *mddev)
>  	/* stop the array and free an attached data structures.
>  	 * This is called from dm-raid
>  	 */
> -	__md_stop(mddev);
>  	bitmap_destroy(mddev);
> +	__md_stop(mddev);
>  	if (mddev->bio_set)
>  		bioset_free(mddev->bio_set);
>  }
> @@ -5696,6 +5696,20 @@ static int do_md_stop(struct mddev *mddev, int mode,
>  			set_disk_ro(disk, 0);
>  
>  		__md_stop_writes(mddev);
> +
> +		/*
> +		 * Destroy bitmap after all writes are stopped
> +		 */
> +		bitmap_destroy(mddev);
> +		if (mddev->bitmap_info.file) {
> +			struct file *f = mddev->bitmap_info.file;
> +			spin_lock(&mddev->lock);
> +			mddev->bitmap_info.file = NULL;
> +			spin_unlock(&mddev->lock);
> +			fput(f);
> +		}
> +		mddev->bitmap_info.offset = 0;
> +
>  		__md_stop(mddev);
>  		mddev->queue->backing_dev_info.congested_fn = NULL;
>  
> @@ -5720,19 +5734,7 @@ static int do_md_stop(struct mddev *mddev, int mode,
>  	 */
>  	if (mode == 0) {
>  		pr_info("md: %s stopped.\n", mdname(mddev));
> -
> -		bitmap_destroy(mddev);
> -		if (mddev->bitmap_info.file) {
> -			struct file *f = mddev->bitmap_info.file;
> -			spin_lock(&mddev->lock);
> -			mddev->bitmap_info.file = NULL;
> -			spin_unlock(&mddev->lock);
> -			fput(f);
> -		}
> -		mddev->bitmap_info.offset = 0;
> -
>  		export_array(mddev);
> -
>  		md_clean(mddev);
>  		if (mddev->hold_active == UNTIL_STOP)
>  			mddev->hold_active = 0;
> -- 
> 2.6.2
> 
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