linux-kernel - Re: [PATCH scsi] Add NULL checking of return value from scsi_cmd_to

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Message-ID: <1348470210.2475.47.camel@ThinkPad-T420>
Date:	Mon, 24 Sep 2012 15:03:30 +0800
From:	Li Zhong <zhong@...ux.vnet.ibm.com>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-scsi@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH scsi] Add NULL checking of return value from
 scsi_cmd_to_driver()

On Mon, 2012-09-24 at 09:44 +0400, James Bottomley wrote:
> On Mon, 2012-09-24 at 13:30 +0800, Li Zhong wrote:
> > Just noticed that after commit 919f797, it is possible that 
> > scsi_cmd_to_driver() returns NULL. This patch adds the NULL checking for drv 
> > returned from the above function. 
> > 
> > Maybe it is not possible at run time, but from the code itself, we'd better
> > have this check?  
> 
> There's not much point having a check that never trips, unless it's an
> assert, in which case a NULL deref does that.  All it does is add
> pointless instructions to the critical path.  only REQ_TYPE_BLOCK_PC
> commands can be submitted without a driver, so the check above would
> seem to preclude that.

Hi James, 

Thank you, it sounds reasonable to me. Let's drop it. 

Thanks, Zhong

> James
> 
> 


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