[dm-devel] [PATCH] dm-mpath: always return reservation conflict

[Christoph Hellwig]

ping?

On Tue, Aug 02, 2016 at 02:36:32PM +0200, Christoph Hellwig wrote:
> From: Hannes Reinecke <hare at suse.de>
> 
> If dm-mpath encounters an reservation conflict it should not fail the
> path (as communication with the target is not affected) but should
> rather retry on another path. However, in doing so we might be inducing
> a ping-pong between paths, with no guarantee of any forward progress.
> 
> And arguably a reservation conflict is an unexpected error, so we should
> be passing it upwards to allow the application to take appropriate steps.
> 
> Signed-off-by: Hannes Reinecke <hare at suse.de>
> Acked-by: Christoph Hellwig <hch at lst.de>
> Tested-by: Christoph Hellwig <hch at lst.de>
> ---
>  drivers/md/dm-mpath.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> index 7eac080..8d2f916 100644
> --- a/drivers/md/dm-mpath.c
> +++ b/drivers/md/dm-mpath.c
> @@ -1555,16 +1555,22 @@ static int do_end_io(struct multipath *m, struct request *clone,
>  	if (noretry_error(error))
>  		return error;
>  
> -	if (mpio->pgpath)
> +	/*
> +	 * EBADE signals an reservation conflict.
> +	 * We shouldn't fail the path here as we can communicate with
> +	 * the target. We should failover to the next path, but in
> +	 * doing so we might be causing a ping-pong between paths.
> +	 * So just return the reservation conflict error.
> +	 */
> +	if (error == -EBADE)
> +		r = error;
> +	else if (mpio->pgpath)
>  		fail_path(mpio->pgpath);
>  
>  	if (!atomic_read(&m->nr_valid_paths)) {
>  		if (!test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
>  			if (!must_push_back_rq(m))
>  				r = -EIO;
> -		} else {
> -			if (error == -EBADE)
> -				r = error;
>  		}
>  	}
>  
> -- 
> 2.1.4
> 
> --
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---end quoted text---