Re: [PATCH] IB/srp: Process REQ_PREEMPT requests correctly

[Mike Christie <michaelc-hcNo3dDEHLuVc3sceRu5cw@public.gmane.org>]

On 01/30/2015 08:34 AM, Bart Van Assche wrote:
> On 01/30/15 03:06, Mike Christie wrote:
>> I think I figured this out. I think we want to change the
>> scsi_prep_state_check check instead of each driver/class.
>>
>> It looks like for the SDEV_QUIESCE state we want to allow REQ_PREEMPT
>> commands. James would know best, but I think SPI needs that ability.
>>
>> For SDEV_BLOCK/SDEV_CREATED_BLOCK, it looks like drivers/classes that
>> use that state do not want any commands to be queued at that time,
>> because the transport is normally down.
> 
> Hello Mike,
> 
> Is something like the patch below what you had in mind ?
> 
> Bart.
> 
> [PATCH] Defer processing of REQ_PREEMPT requests for blocked devices
> 
> SCSI transport drivers and SCSI LLDs block a SCSI device if the
> transport layer is not operational. This means that in this state
> no requests should be processed, even if the REQ_PREEMPT flag has
> been set. This patch avoids that a rescan shortly after a cable
> pull sporadically triggers the following kernel oops:
> 
> BUG: unable to handle kernel paging request at ffffc9001a6bc084
> IP: [<ffffffffa04e08f2>] mlx4_ib_post_send+0xd2/0xb30 [mlx4_ib]
> Process rescan-scsi-bus (pid: 9241, threadinfo ffff88053484a000, task ffff880534aae100)
> Call Trace:
>  [<ffffffffa0718135>] srp_post_send+0x65/0x70 [ib_srp]
>  [<ffffffffa071b9df>] srp_queuecommand+0x1cf/0x3e0 [ib_srp]
>  [<ffffffffa0001ff1>] scsi_dispatch_cmd+0x101/0x280 [scsi_mod]
>  [<ffffffffa0009ad1>] scsi_request_fn+0x411/0x4d0 [scsi_mod]
>  [<ffffffff81223b37>] __blk_run_queue+0x27/0x30
>  [<ffffffff8122a8d2>] blk_execute_rq_nowait+0x82/0x110
>  [<ffffffff8122a9c2>] blk_execute_rq+0x62/0xf0
>  [<ffffffffa000b0e8>] scsi_execute+0xe8/0x190 [scsi_mod]
>  [<ffffffffa000b2f3>] scsi_execute_req+0xa3/0x130 [scsi_mod]
>  [<ffffffffa000c1aa>] scsi_probe_lun+0x17a/0x450 [scsi_mod]
>  [<ffffffffa000ce86>] scsi_probe_and_add_lun+0x156/0x480 [scsi_mod]
>  [<ffffffffa000dc2f>] __scsi_scan_target+0xdf/0x1f0 [scsi_mod]
>  [<ffffffffa000dfa3>] scsi_scan_host_selected+0x183/0x1c0 [scsi_mod]
>  [<ffffffffa000edfb>] scsi_scan+0xdb/0xe0 [scsi_mod]
>  [<ffffffffa000ee13>] store_scan+0x13/0x20 [scsi_mod]
>  [<ffffffff811c8d9b>] sysfs_write_file+0xcb/0x160
>  [<ffffffff811589de>] vfs_write+0xce/0x140
>  [<ffffffff81158b53>] sys_write+0x53/0xa0
>  [<ffffffff81464592>] system_call_fastpath+0x16/0x1b
>  [<00007f611c9d9300>] 0x7f611c9d92ff
> 
> ---
>  drivers/scsi/scsi_lib.c   | 4 +++-
>  include/linux/blk_types.h | 4 +++-
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 17bb541..7129701 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1311,9 +1311,11 @@ scsi_prep_state_check(struct scsi_device *sdev, struct request *req)
>  				    "rejecting I/O to dead device\n");
>  			ret = BLKPREP_KILL;
>  			break;
> -		case SDEV_QUIESCE:
>  		case SDEV_BLOCK:
>  		case SDEV_CREATED_BLOCK:
> +			ret = BLKPREP_DEFER;
> +			break;
> +		case SDEV_QUIESCE:
>  			/*
>  			 * If the devices is blocked we defer normal commands.
>  			 */
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index c294e3e..a1b25e3 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -181,7 +181,9 @@ enum rq_flag_bits {
>  	__REQ_ELVPRIV,		/* elevator private data attached */
>  	__REQ_FAILED,		/* set if the request failed */
>  	__REQ_QUIET,		/* don't worry about errors */
> -	__REQ_PREEMPT,		/* set for "ide_preempt" requests */
> +	__REQ_PREEMPT,		/* set for "ide_preempt" requests and also
> +				   for requests for which the SCSI "quiesce"
> +				   state must be ignored. */
>  	__REQ_ALLOCED,		/* request came from our alloc pool */
>  	__REQ_COPY_USER,	/* contains copies of user pages */
>  	__REQ_FLUSH_SEQ,	/* request for flush sequence */
> 

Yeah. Did some basic tests and it works for me with iscsi and fc. Will
try to do some real testing over the weekend.
--
To unsubscribe from this list: send the line "unsubscribe linux-rdma" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html