From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
linux-scsi@vger.kernel.org,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
"Martin K. Petersen" <mkp@mkp.net>
Subject: Re: [PATCH scsi] Add NULL checking of return value from scsi_cmd_to_driver()
Date: Mon, 24 Sep 2012 11:35:04 +0400 [thread overview]
Message-ID: <1348472104.2467.8.camel@dabdike> (raw)
In-Reply-To: <1348470210.2475.47.camel@ThinkPad-T420>
On Mon, 2012-09-24 at 15:03 +0800, Li Zhong wrote:
> 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.
Well, there is another thing you might do: The path length of
scsi_cmd_to_driver() increased a lot thanks to 18a4d0a22ed6 it might be
worth getting it back to what it was (this looks to be doable with the
same != REQ_TYPE_BLOCK_PC test in the error handler. Plus, I think it
fixes a bug where you get different behaviours from REQ_TYPE_BLOCK_PC
commands when a driver is and isn't attached (I've cc'd Martin to see
what he thinks).
James
next prev parent reply other threads:[~2012-09-24 7:35 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-24 5:30 [PATCH scsi] Add NULL checking of return value from scsi_cmd_to_driver() Li Zhong
2012-09-24 5:44 ` James Bottomley
2012-09-24 7:03 ` Li Zhong
2012-09-24 7:35 ` James Bottomley [this message]
2012-09-24 9:25 ` Li Zhong
2012-09-24 9:33 ` James Bottomley
2012-09-27 2:02 ` Martin K. Petersen
2012-09-27 4:44 ` James Bottomley
2012-09-27 9:51 ` [PATCH scsi] Short the path length of scsi_cmd_to_driver() Li Zhong
2012-09-27 17:43 ` Martin K. Petersen
2012-09-28 7:13 ` Li Zhong
2012-09-28 7:45 ` James Bottomley
2012-09-27 17:41 ` [PATCH scsi] Add NULL checking of return value from scsi_cmd_to_driver() Martin K. Petersen
2012-09-28 7:48 ` James Bottomley
2012-09-29 4:23 ` [PATCH v2 scsi] Short the path length of scsi_cmd_to_driver() Li Zhong
2012-10-02 22:22 ` Martin K. Petersen
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