Re: [RFC v3 01/15] scsi: Drop struct Scsi_Host->host_lock usage in scsi_dispatch_cmd()

[Brian King <brking@linux.vnet.ibm.com>]

On 09/23/2010 06:37 PM, Nicholas A. Bellinger wrote:
> @@ -651,7 +655,6 @@ static inline void scsi_cmd_get_serial(struct Scsi_Host *host, struct scsi_cmnd
>  int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
>  {
>  	struct Scsi_Host *host = cmd->device->host;
> -	unsigned long flags = 0;
>  	unsigned long timeout;
>  	int rtn = 0;
> 
> @@ -736,15 +739,11 @@ int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
>  		scsi_done(cmd);
>  		goto out;
>  	}
> -
> -	spin_lock_irqsave(host->host_lock, flags);
>  	/*
> -	 * AK: unlikely race here: for some reason the timer could
> -	 * expire before the serial number is set up below.
> -	 *
> -	 * TODO: kill serial or move to blk layer
> +	 * Note that scsi_cmd_get_serial() used to be called here, but
> +	 * now we expect the legacy SCSI LLDs that actually need this
> +	 * to call it directly within their SHT->queuecommand() caller.
>  	 */
> -	scsi_cmd_get_serial(host, cmd); 
> 
>  	if (unlikely(host->shost_state == SHOST_DEL)) {
>  		cmd->result = (DID_NO_CONNECT << 16);
> @@ -753,7 +752,7 @@ int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
>  		trace_scsi_dispatch_cmd_start(cmd);
>  		rtn = host->hostt->queuecommand(cmd, scsi_done);
>  	}
> -	spin_unlock_irqrestore(host->host_lock, flags);
> +
>  	if (rtn) {
>  		trace_scsi_dispatch_cmd_error(cmd, rtn);
>  		if (rtn != SCSI_MLQUEUE_DEVICE_BUSY &&

Are you planning a future revision that moves the acquiring of the host lock
into the LLDD's queuecommand for all the other drivers you don't currently
touch in this patch set?

-- 
Brian King
Linux on Power Virtualization
IBM Linux Technology Center