Re: [PATCH v3 0/8] dm: add request-based blk-mq support

[Bart Van Assche <bvanassche@acm.org>]

On 12/22/14 19:49, Mike Snitzer wrote:
> On Mon, Dec 22 2014 at 10:28am -0500,
> Bart Van Assche <bvanassche@acm.org> wrote:
>> Good news: with this patch my standard SRP multipath test ran fine for
>> several hours, after which I stopped the test.
> 
> Great, thanks for testing!  Did you happen to look at the performance of
> your testing?  If so, is it comparable/better/worse?

Hello Mike,

I have tried to run a performance comparison but after I had finished
the measurements without multipath and when I started multipathd I ran
into the following (typed over from the console):

BUG: unable to handle kernel NULL pointer dereference at 0000318
IP: scsi_setup_cmnd+0xe8 [scsi_mod]
Workqueue: kblockd blk_mq_run_work_fn
Call Trace:
scsi_queue_rq+0x5a5
__blk_mq_run_hw_queue+0x1cb
blk_mq_run_work_fn+0xd
process_one_work+0x133
worker_thread+0x11b
kthread+0xcd

gdb translates the above address as follows:

(gdb) list *(scsi_setup_cmnd+0xe8)
0x9568 is in scsi_setup_cmnd (include/scsi/scsi_cmnd.h:155).
150     }
151
152     /* make sure not to use it with REQ_TYPE_BLOCK_PC commands */
153     static inline struct scsi_driver *scsi_cmd_to_driver(struct scsi_cmnd *cmd)
154     {
155             return *(struct scsi_driver **)cmd->request->rq_disk->private_data;
156     }
157
158     extern struct scsi_cmnd *scsi_get_command(struct scsi_device *, gfp_t);
159     extern void scsi_put_command(struct scsi_cmnd *);

Bart.