Re: v3.15 dm-mpath regression: cable pull test causes I/O hang

[Bart Van Assche <bvanassche@acm.org>]

On 07/08/14 02:55, Junichi Nomura wrote:
> pg_ready() checks the current state of the multipath and may return
> false even if a new IO is needed to change the state.
> 
> OTOH, if multipath_busy() returns busy, a new IO will not be sent
> to multipath target and the state change won't happen. That results
> in lock up.
> 
> The intent of multipath_busy() is to avoid unnecessary cycles of
> dequeue + request_fn + requeue if it is known that multipath device
> will requeue.
> 
> Such situation would be:
>   - path group is being activated
>   - there is no path and the multipath is setup to requeue if no path
> 
> This patch should fix the problem introduced as a part of this commit:
>   commit e809917735ebf1b9a56c24e877ce0d320baee2ec
>   dm mpath: push back requests instead of queueing
> 
> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> index ebfa411..d58343e 100644
> --- a/drivers/md/dm-mpath.c
> +++ b/drivers/md/dm-mpath.c
> @@ -1620,8 +1620,9 @@ static int multipath_busy(struct dm_target *ti)
>  
>  	spin_lock_irqsave(&m->lock, flags);
>  
> -	/* pg_init in progress, requeue until done */
> -	if (!pg_ready(m)) {
> +	/* pg_init in progress or no paths available */
> +	if (m->pg_init_in_progress ||
> +	    (!m->nr_valid_paths && m->queue_if_no_path)) {
>  		busy = 1;
>  		goto out;
>  	}
> 

This patch seems to fix the issue reported at the start of this thread -
with this patch applied my test passes.

Thanks !

Bart.