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

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Date:	Mon, 24 Sep 2012 09:44:53 +0400
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Li Zhong <zhong@...ux.vnet.ibm.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 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.

James


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