IB/srp: Process REQ_PREEMPT requests correctly

PATCH In review Bart Van Assche 4 participants 6 messages Jan 29, 2015 – Jan 30, 2015 2 messages not in the archive

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SCSI Block layer InfiniBand SCSI RDMA protocol (SRP) initiator

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Bart Van Assche

author

2015-01-29 13:02 UTC #0 lore raw

PATCH 1/1 IB/srp: Process REQ_PREEMPT requests correctly

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 <[email protected]>

Signed-off-by Bart Van Assche <[email protected]>

Cc Sagi Grimberg <[email protected]>

Cc <[email protected]>

---
 drivers/infiniband/ulp/srp/ib_srp.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

drivers/infiniband/ulp/srp/ib_srp.c +6 -1

index 0747c05..77a7a2f 100644
@@ -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);

Signature · 1 line

2.1.4

A message that is not in the archive (sent off-list or not yet received): [email protected]

Sagi Grimberg

Reviewed-by

2015-01-29 13:44 UTC #2 lore raw

Quoted 48 lines · Bart Van Assche

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/[email protected]>

Signed-off-by Bart Van Assche <[email protected]>

Cc Sagi Grimberg <sagig-VPRAkNaXOzVWk0Htik3J/[email protected]>

Cc <[email protected]>

---
  drivers/infiniband/ulp/srp/ib_srp.c | 7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)

drivers/infiniband/ulp/srp/ib_srp.c +1 -0

index 0747c05..77a7a2f 100644
@@ -2003,8 +2003,13 @@ static int srp_queuecommand(struct Scsi_Host *shost, struct scsi_cmnd *scmnd)
  	if (in_scsi_eh)
  		mutex_lock(&rport->mutex);
 
+	/*

drivers/infiniband/ulp/srp/ib_srp.c static int srp_queuecommand(struct Scsi_Host *shost, struct scsi_cmnd *scmnd) · line 2015

Quoted 10 lines

drivers/infiniband/ulp/srp/ib_srp.c +5 -1

+	 * 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/[email protected]>

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Mike Christie

2015-01-29 19:38 UTC #3 lore raw

In reply to Bart Van Assche

Quoted 48 lines · Bart Van Assche

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 <[email protected]>

Signed-off-by Bart Van Assche <[email protected]>

Cc Sagi Grimberg <[email protected]>

Cc <[email protected]>

---
  drivers/infiniband/ulp/srp/ib_srp.c | 7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)

drivers/infiniband/ulp/srp/ib_srp.c +1 -0

index 0747c05..77a7a2f 100644
@@ -2003,8 +2003,13 @@ static int srp_queuecommand(struct Scsi_Host *shost, struct scsi_cmnd *scmnd)
  	if (in_scsi_eh)
  		mutex_lock(&rport->mutex);
 
+	/*

drivers/infiniband/ulp/srp/ib_srp.c static int srp_queuecommand(struct Scsi_Host *shost, struct scsi_cmnd *scmnd) · line 2015

Quoted 10 lines

drivers/infiniband/ulp/srp/ib_srp.c +5 -1

+	 * 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.

Mike Christie

2015-01-30 02:06 UTC #4 lore raw

Quoted 62 lines · Mike Christie

Quoted 61 lines · Bart Van Assche

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 <[email protected]>

Signed-off-by Bart Van Assche <[email protected]>

Cc Sagi Grimberg <[email protected]>

Cc <[email protected]>

---
  drivers/infiniband/ulp/srp/ib_srp.c | 7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)

drivers/infiniband/ulp/srp/ib_srp.c +2 -0

index 0747c05..77a7a2f 100644
@@ -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

drivers/infiniband/ulp/srp/ib_srp.c +4 -1

+     * 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;

Quoted 7 lines

Quoted 2 lines
      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.

Bart Van Assche

author

2015-01-30 14:34 UTC #5 lore raw

Quoted 9 lines · Mike Christie

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(-)

drivers/scsi/scsi_lib.c +3 -1

index 17bb541..7129701 100644
@@ -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.
 			 */

include/linux/blk_types.h +3 -1

index c294e3e..a1b25e3 100644
@@ -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 */

Signature · 1 line

2.1.4

A message that is not in the archive (sent off-list or not yet received): [email protected]

Mike Christie

2015-01-30 20:18 UTC #7 lore raw

Quoted 78 lines · Bart Van Assche

Quoted 9 lines · Mike Christie
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(-)
drivers/scsi/scsi_lib.c +3 -1
index 17bb541..7129701 100644
@@ -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.
 			 */
include/linux/blk_types.h +0 -0
index c294e3e..a1b25e3 100644

include/linux/blk_types.h enum rq_flag_bits { · line 189

Quoted 10 lines

include/linux/blk_types.h +3 -1

@@ -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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