Re: Changes to Linux/SCSI target mode infrastructure for v2.6.28

["Nicholas A. Bellinger" <nab@linux-iscsi.org>]

On Mon, 2008-12-01 at 17:52 -0800, Nicholas A. Bellinger wrote:
> Greetings Tomo-san and Co,
> 
> With the ongoing work in Linux/SCSI for v2.6.28 to map target mode
> struct scatterlist memory directly down to struct scsi_cmnd without the
> need for a intermediate struct bio as with the existing
> scsi_execute_async(), I have started the porting process for the
> Linux/SCSI subsystem plugin in generic target core v3.0
> (lio-core-2.6.git) on v2.6.28-rc6.
> 
> So far, using struct request for ICF_SCSI_CONTROL_NONSG_IO_CDB is up
> using blk_rq_map_kern(), as well as ICF_SCSI_NON_DATA_CDB ops using
> struct request.  In order to get the first READ_10s of type
> ICF_SCSI_DATA_SG_IO_CDB to work, I had to add a temporary
> EXPORT_SYMBOL_GPL() for drivers/scsi/scsi_lib.c:scsi_req_map_sg() in
> lio-core-2.6.git for v2.6.28-rc6 in order to get TYPE_DISK up using an
> software emulated MPT-Fusion HBA driver with struct request.  I have
> been looking at drivers/scsi/scsi_tgt_lib.c() (which currently uses
> struct request), and I figure we need something similar for the generic
> target infrastructure, although __scsi_get_command() and
> __scsi_put_command() are currently used in that code.
> 
> Below is what my patch looks like so far, I will probably just end up
> commiting an temporary ifdef to keep scsi_execute_async() until the
> proper pieces are in place and the other issues are resolved below.
> >From there I will be able to drop in the proper upstream mapping bits
> for struct scatterlist in
> drivers/lio-core/target_core_pscsi.c:pscsi_map_task_SG() get rid of
> scsi_req_map_sg() usage all together.
> 
> So far during my initial testing, I am running into a two different
> exceptions.  One NULL pointer deference OOPS after half dozen Open/iSCSI
> login/logouts in block/elevator.c:elv_dequeue_request().   Here is the
> trace from SCSI softirq context:
> 
> http://linux-iscsi.org/builds/user/nab/2.6.28-rc6-oops-0.png
> http://linux-iscsi.org/builds/user/nab/2.6.28-rc6-oops-1.png
> 
> The other one is a BUG_ON in blk/blk-timeout.c:177 in blk_add_timeout()
> that happens after a few hundred MB of READ_10 traffic, which also
> appears to pass through elv_dequeue_request() at some point:
> 
> http://linux-iscsi.org/builds/user/nab/2.6.28-rc6-oops-2.png
> http://linux-iscsi.org/builds/user/nab/2.6.28-rc6-oops-4.png
> 

Ok, I just saw this patch:

[PATCH 2.6.28-rc6] block: internal dequeue shouldn't start timer

at http://lkml.org/lkml/2008/11/27/394.

It sounds very similar and I will try it out and see if it resolves the
issues above.

Thanks,

--nab