[PATCH] IB/srp: Process REQ_PREEMPT requests correctly

[PATCH] IB/srp: Process REQ_PREEMPT requests correctly

[Bart Van Assche]

Delay REQ_PREEMPT requests submitted against a blocked device
until the device is unblocked by returning SCSI_MLQUEUE_HOST_BUSY
to the SCSI mid-layer. This 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

Reported-by: Max Gurtuvoy <maxg@mellanox.com>
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: <stable@vger.kernel.org>
---
 drivers/infiniband/ulp/srp/ib_srp.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
index 0747c05..77a7a2f 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.c
+++ b/drivers/infiniband/ulp/srp/ib_srp.c
@@ -2003,8 +2003,13 @@ static int srp_queuecommand(struct Scsi_Host *shost, struct scsi_cmnd *scmnd)
 	if (in_scsi_eh)
 		mutex_lock(&rport->mutex);
 
+	/*
+	 * The "blocked" state of SCSI devices is ignored by the SCSI core for
+	 * REQ_PREEMPT requests. Hence the explicit check below for the SCSI
+	 * device state.
+	 */
 	scmnd->result = srp_chkready(target->rport);
-	if (unlikely(scmnd->result))
+	if (unlikely(scmnd->result != 0 || scsi_device_blocked(scmnd->device)))
 		goto err;
 
 	WARN_ON_ONCE(scmnd->request->tag < 0);
-- 
2.1.4

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

[Sagi Grimberg]

On 1/29/2015 3:02 PM, Bart Van Assche wrote:
> Delay REQ_PREEMPT requests submitted against a blocked device
> until the device is unblocked by returning SCSI_MLQUEUE_HOST_BUSY
> to the SCSI mid-layer. This 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
>
> Reported-by: Max Gurtuvoy <maxg-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
> Signed-off-by: Bart Van Assche <bart.vanassche-XdAiOPVOjttBDgjK7y7TUQ@public.gmane.org>
> Cc: Sagi Grimberg <sagig-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
> Cc: <stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
> ---
>   drivers/infiniband/ulp/srp/ib_srp.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
> index 0747c05..77a7a2f 100644
> --- a/drivers/infiniband/ulp/srp/ib_srp.c
> +++ b/drivers/infiniband/ulp/srp/ib_srp.c
> @@ -2003,8 +2003,13 @@ static int srp_queuecommand(struct Scsi_Host *shost, struct scsi_cmnd *scmnd)
>   	if (in_scsi_eh)
>   		mutex_lock(&rport->mutex);
>
> +	/*
> +	 * The "blocked" state of SCSI devices is ignored by the SCSI core for
> +	 * REQ_PREEMPT requests. Hence the explicit check below for the SCSI
> +	 * device state.
> +	 */
>   	scmnd->result = srp_chkready(target->rport);
> -	if (unlikely(scmnd->result))
> +	if (unlikely(scmnd->result != 0 || scsi_device_blocked(scmnd->device)))
>   		goto err;
>
>   	WARN_ON_ONCE(scmnd->request->tag < 0);
>


Yep...

Reviewed-by: Sagi Grimberg <sagig-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
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Re: [PATCH] IB/srp: Process REQ_PREEMPT requests correctly

[Mike Christie]

On 1/29/15, 7:02 AM, Bart Van Assche wrote:
> Delay REQ_PREEMPT requests submitted against a blocked device
> until the device is unblocked by returning SCSI_MLQUEUE_HOST_BUSY
> to the SCSI mid-layer. This 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
>
> Reported-by: Max Gurtuvoy <maxg@mellanox.com>
> Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
> Cc: Sagi Grimberg <sagig@mellanox.com>
> Cc: <stable@vger.kernel.org>
> ---
>   drivers/infiniband/ulp/srp/ib_srp.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
> index 0747c05..77a7a2f 100644
> --- a/drivers/infiniband/ulp/srp/ib_srp.c
> +++ b/drivers/infiniband/ulp/srp/ib_srp.c
> @@ -2003,8 +2003,13 @@ static int srp_queuecommand(struct Scsi_Host *shost, struct scsi_cmnd *scmnd)
>   	if (in_scsi_eh)
>   		mutex_lock(&rport->mutex);
>
> +	/*
> +	 * The "blocked" state of SCSI devices is ignored by the SCSI core for
> +	 * REQ_PREEMPT requests. Hence the explicit check below for the SCSI
> +	 * device state.
> +	 */
>   	scmnd->result = srp_chkready(target->rport);
> -	if (unlikely(scmnd->result))
> +	if (unlikely(scmnd->result != 0 || scsi_device_blocked(scmnd->device)))
>   		goto err;
>
>   	WARN_ON_ONCE(scmnd->request->tag < 0);
>

What is the case where a driver blocks the device and can handle or 
wants commands? iSCSI and FC also do not want commands, even PREEMPT 
ones, at this time. It looks like they have been hitting internal checks 
to prevent hitting similar issues.

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

[Mike Christie]

On 1/29/15, 1:38 PM, Mike Christie wrote:
> On 1/29/15, 7:02 AM, Bart Van Assche wrote:
>> Delay REQ_PREEMPT requests submitted against a blocked device
>> until the device is unblocked by returning SCSI_MLQUEUE_HOST_BUSY
>> to the SCSI mid-layer. This 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
>>
>> Reported-by: Max Gurtuvoy <maxg@mellanox.com>
>> Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
>> Cc: Sagi Grimberg <sagig@mellanox.com>
>> Cc: <stable@vger.kernel.org>
>> ---
>>   drivers/infiniband/ulp/srp/ib_srp.c | 7 ++++++-
>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/infiniband/ulp/srp/ib_srp.c
>> b/drivers/infiniband/ulp/srp/ib_srp.c
>> index 0747c05..77a7a2f 100644
>> --- a/drivers/infiniband/ulp/srp/ib_srp.c
>> +++ b/drivers/infiniband/ulp/srp/ib_srp.c
>> @@ -2003,8 +2003,13 @@ static int srp_queuecommand(struct Scsi_Host
>> *shost, struct scsi_cmnd *scmnd)
>>       if (in_scsi_eh)
>>           mutex_lock(&rport->mutex);
>>
>> +    /*
>> +     * The "blocked" state of SCSI devices is ignored by the SCSI
>> core for
>> +     * REQ_PREEMPT requests. Hence the explicit check below for the SCSI
>> +     * device state.
>> +     */
>>       scmnd->result = srp_chkready(target->rport);
>> -    if (unlikely(scmnd->result))
>> +    if (unlikely(scmnd->result != 0 ||
>> scsi_device_blocked(scmnd->device)))
>>           goto err;
>>
>>       WARN_ON_ONCE(scmnd->request->tag < 0);
>>
>
> What is the case where a driver blocks the device and can handle or
> wants commands? iSCSI and FC also do not want commands, even PREEMPT
> ones, at this time. It looks like they have been hitting internal checks
> to prevent hitting similar issues.

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.

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

[Bart Van Assche]

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 */
-- 
2.1.4

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

[Mike Christie]

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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