[PATCH 6/8] block: drivers: complete request locally from blk_mq_tagset_busy_iter

[Bart Van Assche]

On 4/25/21 1:57 AM, Ming Lei wrote:
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index c289991ffaed..7cbaee282b6d 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1568,7 +1568,11 @@ static void scsi_mq_done(struct scsi_cmnd *cmd)
>  	if (unlikely(test_and_set_bit(SCMD_STATE_COMPLETE, &cmd->state)))
>  		return;
>  	trace_scsi_dispatch_cmd_done(cmd);
> -	blk_mq_complete_request(cmd->request);
> +
> +	if (unlikely(host_byte(cmd->result) != DID_OK))
> +		blk_mq_complete_request_locally(cmd->request);
> +	else
> +		blk_mq_complete_request(cmd->request);
>  }

This change is so tricky that it deserves a comment.

An even better approach would be *not* to export
blk_mq_complete_request_locally() from the block layer to block drivers
and instead modify the block layer such that it completes a request on
the same CPU if request completion happens from inside the context of a
tag iteration function. That would save driver writers the trouble of
learning yet another block layer API.

Bart.