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

Mike Christie
2015-01-30T20:18:59Z

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.
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