linux-kernel - Re: [RFC v3 01/15] scsi: Drop struct Scsi_Host->host_lock usage in scsi_dispatch

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Date:	Fri, 24 Sep 2010 08:41:20 -0500
From:	Brian King <brking@...ux.vnet.ibm.com>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
CC:	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Vasu Dev <vasu.dev@...ux.intel.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	James Bottomley <James.Bottomley@...e.de>,
	Mike Christie <michaelc@...wisc.edu>,
	James Smart <james.smart@...lex.com>,
	Andrew Vasquez <andrew.vasquez@...gic.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Hannes Reinecke <hare@...e.de>,
	Joe Eykholt <jeykholt@...co.com>,
	Christoph Hellwig <hch@....de>,
	MPTFusionLinux <DL-MPTFusionLinux@....com>,
	"eata.c maintainer" <dario.ballabio@...ind.it>
Subject: Re: [RFC v3 01/15] scsi: Drop struct Scsi_Host->host_lock usage in
 scsi_dispatch_cmd()

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


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