linux-toradex.git/drivers/scsi/hosts.c, branch v5.19-rc3 Linux kernel for Apalis and Colibri modules scsi: core: Refine how we set tag_set NUMA node 2022-04-26T12:10:35+00:00 John Garry john.garry@huawei.com 2022-03-30T11:38:35+00:00 973dac8a8a14a7fcfd4fa0b682851f415eb91b04 For SCSI hosts which enable host_tagset the NUMA node returned from blk_mq_hw_queue_to_node() is NUMA_NO_NODE always. Then, since in scsi_mq_setup_tags() the default we choose for the tag_set NUMA node is NUMA_NO_NODE, we always evaluate the NUMA node as NUMA_NO_NODE in functions like blk_mq_alloc_rq_map(). The reason we get NUMA_NO_NODE from blk_mq_hw_queue_to_node() is that the hctx_idx passed is BLK_MQ_NO_HCTX_IDX - so we can't match against a (HW) queue mapping index. Improve this by defaulting the tag_set NUMA node to the same NUMA node of the SCSI host DMA dev. Link: https://lore.kernel.org/r/1648640315-21419-1-git-send-email-john.garry@huawei.com Signed-off-by: John Garry <john.garry@huawei.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> 
For SCSI hosts which enable host_tagset the NUMA node returned from
blk_mq_hw_queue_to_node() is NUMA_NO_NODE always. Then, since in
scsi_mq_setup_tags() the default we choose for the tag_set NUMA node is
NUMA_NO_NODE, we always evaluate the NUMA node as NUMA_NO_NODE in functions
like blk_mq_alloc_rq_map().

The reason we get NUMA_NO_NODE from blk_mq_hw_queue_to_node() is that the
hctx_idx passed is BLK_MQ_NO_HCTX_IDX - so we can't match against a (HW)
queue mapping index.

Improve this by defaulting the tag_set NUMA node to the same NUMA node of
the SCSI host DMA dev.

Link: https://lore.kernel.org/r/1648640315-21419-1-git-send-email-john.garry@huawei.com
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
scsi: core: Remove Scsi_Host.shost_dev_attr_groups 2021-11-19T03:26:58+00:00 Bart Van Assche bvanassche@acm.org 2021-11-16T22:31:15+00:00 0a84486d6c1da1c2738544d8fc1b07b1d3ce046f Simplify the scsi_host_alloc() implementation by setting the shost_class .dev_groups member instead of copying all host attribute group pointers into the shost_dev_attr_groups[] array. Link: https://lore.kernel.org/r/20211116223115.2103031-1-bvanassche@acm.org Cc: Steffen Maier <maier@linux.ibm.com> Cc: Damien Le Moal <damien.lemoal@wdc.com> Suggested-by: Benjamin Block <bblock@linux.ibm.com> Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com> Signed-off-by: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> 
Simplify the scsi_host_alloc() implementation by setting the shost_class
.dev_groups member instead of copying all host attribute group pointers
into the shost_dev_attr_groups[] array.

Link: https://lore.kernel.org/r/20211116223115.2103031-1-bvanassche@acm.org
Cc: Steffen Maier <maier@linux.ibm.com>
Cc: Damien Le Moal <damien.lemoal@wdc.com>
Suggested-by: Benjamin Block <bblock@linux.ibm.com>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Merge branch '5.15/scsi-fixes' into 5.16/scsi-queue 2021-11-04T01:46:00+00:00 Martin K. Petersen martin.petersen@oracle.com 2021-11-04T01:46:00+00:00 6266f7df38e167a2386ee2747965c4816f32b449 The partial UFS revert in 5.15 is needed for some additional fixes in the 5.16 SCSI tree. Merge the fixes branch. Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> 
The partial UFS revert in 5.15 is needed for some additional fixes in
the 5.16 SCSI tree. Merge the fixes branch.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
scsi: core: Avoid leaving shost->last_reset with stale value if EH does not run 2021-11-04T01:33:50+00:00 Ewan D. Milne emilne@redhat.com 2021-10-29T19:43:10+00:00 5ae17501bc62a49b0b193dcce003f16375f16654 The changes to issue the abort from the scmd->abort_work instead of the EH thread introduced a problem if eh_deadline is used. If aborting the command(s) is successful, and there are never any scmds added to the shost->eh_cmd_q, there is no code path which will reset the ->last_reset value back to zero. The effect of this is that after a successful abort with no EH thread activity, a subsequent timeout, perhaps a long time later, might immediately be considered past a user-set eh_deadline time, and the host will be reset with no attempt at recovery. Fix this by resetting ->last_reset back to zero in scmd_eh_abort_handler() if it is determined that the EH thread will not run to do this. Thanks to Gopinath Marappan for investigating this problem. Link: https://lore.kernel.org/r/20211029194311.17504-2-emilne@redhat.com Fixes: e494f6a72839 ("[SCSI] improved eh timeout handler") Cc: stable@vger.kernel.org Signed-off-by: Ewan D. Milne <emilne@redhat.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> 
The changes to issue the abort from the scmd->abort_work instead of the EH
thread introduced a problem if eh_deadline is used.  If aborting the
command(s) is successful, and there are never any scmds added to the
shost->eh_cmd_q, there is no code path which will reset the ->last_reset
value back to zero.

The effect of this is that after a successful abort with no EH thread
activity, a subsequent timeout, perhaps a long time later, might
immediately be considered past a user-set eh_deadline time, and the host
will be reset with no attempt at recovery.

Fix this by resetting ->last_reset back to zero in scmd_eh_abort_handler()
if it is determined that the EH thread will not run to do this.

Thanks to Gopinath Marappan for investigating this problem.

Link: https://lore.kernel.org/r/20211029194311.17504-2-emilne@redhat.com
Fixes: e494f6a72839 ("[SCSI] improved eh timeout handler")
Cc: stable@vger.kernel.org
Signed-off-by: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
scsi: core: Remove two host template members that are no longer used 2021-10-17T01:45:59+00:00 Bart Van Assche bvanassche@acm.org 2021-10-12T23:35:58+00:00 a47c6b713e89eef9e26ef9b17944fc807510bf3c All SCSI drivers have been converted to use shost_groups and sdev_groups instead of shost_attrs or sdev_attrs. Hence remove shost_attrs and sdev_attrs. Additionally, remove the 'lld_attr_group' members and also the scsi_convert_dev_attrs() function. Link: https://lore.kernel.org/r/20211012233558.4066756-47-bvanassche@acm.org Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Reviewed-by: Benjamin Block <bblock@linux.ibm.com> Signed-off-by: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> 
All SCSI drivers have been converted to use shost_groups and sdev_groups
instead of shost_attrs or sdev_attrs. Hence remove shost_attrs and
sdev_attrs. Additionally, remove the 'lld_attr_group' members and also
the scsi_convert_dev_attrs() function.

Link: https://lore.kernel.org/r/20211012233558.4066756-47-bvanassche@acm.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
scsi: core: Register sysfs attributes earlier 2021-10-17T01:45:52+00:00 Bart Van Assche bvanassche@acm.org 2021-10-12T23:35:13+00:00 92c4b58b15c56298b1b225c1d2e533165b3e32af A quote from Documentation/driver-api/driver-model/device.rst: "Word of warning: While the kernel allows device_create_file() and device_remove_file() to be called on a device at any time, userspace has strict expectations on when attributes get created. When a new device is registered in the kernel, a uevent is generated to notify userspace (like udev) that a new device is available. If attributes are added after the device is registered, then userspace won't get notified and userspace will not know about the new attributes." Hence register SCSI host sysfs attributes before the SCSI host shost_dev uevent is emitted instead of after that event has been emitted. Link: https://lore.kernel.org/r/20211012233558.4066756-2-bvanassche@acm.org Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Reviewed-by: Benjamin Block <bblock@linux.ibm.com> Signed-off-by: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> 
A quote from Documentation/driver-api/driver-model/device.rst:
"Word of warning:  While the kernel allows device_create_file() and
device_remove_file() to be called on a device at any time, userspace has
strict expectations on when attributes get created.  When a new device is
registered in the kernel, a uevent is generated to notify userspace (like
udev) that a new device is available.  If attributes are added after the
device is registered, then userspace won't get notified and userspace will
not know about the new attributes."

Hence register SCSI host sysfs attributes before the SCSI host shost_dev
uevent is emitted instead of after that event has been emitted.

Link: https://lore.kernel.org/r/20211012233558.4066756-2-bvanassche@acm.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
scsi: core: Call scsi_done directly 2021-10-17T01:31:43+00:00 Bart Van Assche bvanassche@acm.org 2021-10-07T20:46:11+00:00 11b68e36b16752ae3a48dc16229958ebc9bb324a Conditional statements are faster than indirect calls. Hence call scsi_done() directly. Since this patch removes the last user of the scsi_done member, also remove that data structure member. Link: https://lore.kernel.org/r/20211007204618.2196847-11-bvanassche@acm.org Reviewed-by: Benjamin Block <bblock@linux.ibm.com> Reviewed-by: Bean Huo <beanhuo@micron.com> Signed-off-by: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> 
Conditional statements are faster than indirect calls. Hence call
scsi_done() directly. Since this patch removes the last user of the
scsi_done member, also remove that data structure member.

Link: https://lore.kernel.org/r/20211007204618.2196847-11-bvanassche@acm.org
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Reviewed-by: Bean Huo <beanhuo@micron.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
scsi: core: pm: Rely on the device driver core for async power management 2021-10-17T01:08:39+00:00 Bart Van Assche bvanassche@acm.org 2021-10-06T21:54:51+00:00 a19a93e4c6a98c9c0f2f5a6db76846f10d7d1f85 Instead of implementing asynchronous resume support in the SCSI core, rely on the device driver core for resuming SCSI devices asynchronously. Instead of only supporting asynchronous resumes, also support asynchronous suspends. Link: https://lore.kernel.org/r/20211006215453.3318929-2-bvanassche@acm.org Cc: Alan Stern <stern@rowland.harvard.edu> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hannes Reinecke <hare@suse.com> Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Martin Kepplinger <martin.kepplinger@puri.sm> Signed-off-by: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> 
Instead of implementing asynchronous resume support in the SCSI core, rely
on the device driver core for resuming SCSI devices asynchronously.
Instead of only supporting asynchronous resumes, also support asynchronous
suspends.

Link: https://lore.kernel.org/r/20211006215453.3318929-2-bvanassche@acm.org
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
scsi: core: Fix shost->cmd_per_lun calculation in scsi_add_host_with_dma() 2021-10-12T16:37:15+00:00 Dexuan Cui decui@microsoft.com 2021-10-08T04:35:46+00:00 50b6cb3516365cb69753b006be2b61c966b70588 After commit ea2f0f77538c ("scsi: core: Cap scsi_host cmd_per_lun at can_queue"), a 416-CPU VM running on Hyper-V hangs during boot because the hv_storvsc driver sets scsi_driver.can_queue to an integer value that exceeds SHRT_MAX, and hence scsi_add_host_with_dma() sets shost->cmd_per_lun to a negative "short" value. Use min_t(int, ...) to work around the issue. Link: https://lore.kernel.org/r/20211008043546.6006-1-decui@microsoft.com Fixes: ea2f0f77538c ("scsi: core: Cap scsi_host cmd_per_lun at can_queue") Cc: stable@vger.kernel.org Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: John Garry <john.garry@huawei.com> Signed-off-by: Dexuan Cui <decui@microsoft.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> 
After commit ea2f0f77538c ("scsi: core: Cap scsi_host cmd_per_lun at
can_queue"), a 416-CPU VM running on Hyper-V hangs during boot because the
hv_storvsc driver sets scsi_driver.can_queue to an integer value that
exceeds SHRT_MAX, and hence scsi_add_host_with_dma() sets
shost->cmd_per_lun to a negative "short" value.

Use min_t(int, ...) to work around the issue.

Link: https://lore.kernel.org/r/20211008043546.6006-1-decui@microsoft.com
Fixes: ea2f0f77538c ("scsi: core: Cap scsi_host cmd_per_lun at can_queue")
Cc: stable@vger.kernel.org
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: John Garry <john.garry@huawei.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
scsi: core: Fix bad pointer dereference when ehandler kthread is invalid 2021-07-13T01:46:24+00:00 Tyrel Datwyler tyreld@linux.ibm.com 2021-07-01T19:56:59+00:00 93aa71ad7379900e61c8adff6a710a4c18c7c99b Commit 66a834d09293 ("scsi: core: Fix error handling of scsi_host_alloc()") changed the allocation logic to call put_device() to perform host cleanup with the assumption that IDA removal and stopping the kthread would properly be performed in scsi_host_dev_release(). However, in the unlikely case that the error handler thread fails to spawn, shost->ehandler is set to ERR_PTR(-ENOMEM). The error handler cleanup code in scsi_host_dev_release() will call kthread_stop() if shost->ehandler != NULL which will always be the case whether the kthread was successfully spawned or not. In the case that it failed to spawn this has the nasty side effect of trying to dereference an invalid pointer when kthread_stop() is called. The following splat provides an example of this behavior in the wild: scsi host11: error handler thread failed to spawn, error = -4 Kernel attempted to read user page (10c) - exploit attempt? (uid: 0) BUG: Kernel NULL pointer dereference on read at 0x0000010c Faulting instruction address: 0xc00000000818e9a8 Oops: Kernel access of bad area, sig: 11 [#1] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries Modules linked in: ibmvscsi(+) scsi_transport_srp dm_multipath dm_mirror dm_region hash dm_log dm_mod fuse overlay squashfs loop CPU: 12 PID: 274 Comm: systemd-udevd Not tainted 5.13.0-rc7 #1 NIP: c00000000818e9a8 LR: c0000000089846e8 CTR: 0000000000007ee8 REGS: c000000037d12ea0 TRAP: 0300 Not tainted (5.13.0-rc7) MSR: 800000000280b033 &lt;SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE&gt; CR: 28228228 XER: 20040001 CFAR: c0000000089846e4 DAR: 000000000000010c DSISR: 40000000 IRQMASK: 0 GPR00: c0000000089846e8 c000000037d13140 c000000009cc1100 fffffffffffffffc GPR04: 0000000000000001 0000000000000000 0000000000000000 c000000037dc0000 GPR08: 0000000000000000 c000000037dc0000 0000000000000001 00000000fffff7ff GPR12: 0000000000008000 c00000000a049000 c000000037d13d00 000000011134d5a0 GPR16: 0000000000001740 c0080000190d0000 c0080000190d1740 c000000009129288 GPR20: c000000037d13bc0 0000000000000001 c000000037d13bc0 c0080000190b7898 GPR24: c0080000190b7708 0000000000000000 c000000033bb2c48 0000000000000000 GPR28: c000000046b28280 0000000000000000 000000000000010c fffffffffffffffc NIP [c00000000818e9a8] kthread_stop+0x38/0x230 LR [c0000000089846e8] scsi_host_dev_release+0x98/0x160 Call Trace: [c000000033bb2c48] 0xc000000033bb2c48 (unreliable) [c0000000089846e8] scsi_host_dev_release+0x98/0x160 [c00000000891e960] device_release+0x60/0x100 [c0000000087e55c4] kobject_release+0x84/0x210 [c00000000891ec78] put_device+0x28/0x40 [c000000008984ea4] scsi_host_alloc+0x314/0x430 [c0080000190b38bc] ibmvscsi_probe+0x54/0xad0 [ibmvscsi] [c000000008110104] vio_bus_probe+0xa4/0x4b0 [c00000000892a860] really_probe+0x140/0x680 [c00000000892aefc] driver_probe_device+0x15c/0x200 [c00000000892b63c] device_driver_attach+0xcc/0xe0 [c00000000892b740] __driver_attach+0xf0/0x200 [c000000008926f28] bus_for_each_dev+0xa8/0x130 [c000000008929ce4] driver_attach+0x34/0x50 [c000000008928fc0] bus_add_driver+0x1b0/0x300 [c00000000892c798] driver_register+0x98/0x1a0 [c00000000810eb60] __vio_register_driver+0x80/0xe0 [c0080000190b4a30] ibmvscsi_module_init+0x9c/0xdc [ibmvscsi] [c0000000080121d0] do_one_initcall+0x60/0x2d0 [c000000008261abc] do_init_module+0x7c/0x320 [c000000008265700] load_module+0x2350/0x25b0 [c000000008265cb4] __do_sys_finit_module+0xd4/0x160 [c000000008031110] system_call_exception+0x150/0x2d0 [c00000000800d35c] system_call_common+0xec/0x278 Fix this be nulling shost->ehandler when the kthread fails to spawn. Link: https://lore.kernel.org/r/20210701195659.3185475-1-tyreld@linux.ibm.com Fixes: 66a834d09293 ("scsi: core: Fix error handling of scsi_host_alloc()") Cc: stable@vger.kernel.org Reviewed-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> 
Commit 66a834d09293 ("scsi: core: Fix error handling of scsi_host_alloc()")
changed the allocation logic to call put_device() to perform host cleanup
with the assumption that IDA removal and stopping the kthread would
properly be performed in scsi_host_dev_release(). However, in the unlikely
case that the error handler thread fails to spawn, shost->ehandler is set
to ERR_PTR(-ENOMEM).

The error handler cleanup code in scsi_host_dev_release() will call
kthread_stop() if shost->ehandler != NULL which will always be the case
whether the kthread was successfully spawned or not. In the case that it
failed to spawn this has the nasty side effect of trying to dereference an
invalid pointer when kthread_stop() is called. The following splat provides
an example of this behavior in the wild:

scsi host11: error handler thread failed to spawn, error = -4
Kernel attempted to read user page (10c) - exploit attempt? (uid: 0)
BUG: Kernel NULL pointer dereference on read at 0x0000010c
Faulting instruction address: 0xc00000000818e9a8
Oops: Kernel access of bad area, sig: 11 [#1]
LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
Modules linked in: ibmvscsi(+) scsi_transport_srp dm_multipath dm_mirror dm_region
 hash dm_log dm_mod fuse overlay squashfs loop
CPU: 12 PID: 274 Comm: systemd-udevd Not tainted 5.13.0-rc7 #1
NIP:  c00000000818e9a8 LR: c0000000089846e8 CTR: 0000000000007ee8
REGS: c000000037d12ea0 TRAP: 0300   Not tainted  (5.13.0-rc7)
MSR:  800000000280b033 &lt;SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE&gt;  CR: 28228228
XER: 20040001
CFAR: c0000000089846e4 DAR: 000000000000010c DSISR: 40000000 IRQMASK: 0
GPR00: c0000000089846e8 c000000037d13140 c000000009cc1100 fffffffffffffffc
GPR04: 0000000000000001 0000000000000000 0000000000000000 c000000037dc0000
GPR08: 0000000000000000 c000000037dc0000 0000000000000001 00000000fffff7ff
GPR12: 0000000000008000 c00000000a049000 c000000037d13d00 000000011134d5a0
GPR16: 0000000000001740 c0080000190d0000 c0080000190d1740 c000000009129288
GPR20: c000000037d13bc0 0000000000000001 c000000037d13bc0 c0080000190b7898
GPR24: c0080000190b7708 0000000000000000 c000000033bb2c48 0000000000000000
GPR28: c000000046b28280 0000000000000000 000000000000010c fffffffffffffffc
NIP [c00000000818e9a8] kthread_stop+0x38/0x230
LR [c0000000089846e8] scsi_host_dev_release+0x98/0x160
Call Trace:
[c000000033bb2c48] 0xc000000033bb2c48 (unreliable)
[c0000000089846e8] scsi_host_dev_release+0x98/0x160
[c00000000891e960] device_release+0x60/0x100
[c0000000087e55c4] kobject_release+0x84/0x210
[c00000000891ec78] put_device+0x28/0x40
[c000000008984ea4] scsi_host_alloc+0x314/0x430
[c0080000190b38bc] ibmvscsi_probe+0x54/0xad0 [ibmvscsi]
[c000000008110104] vio_bus_probe+0xa4/0x4b0
[c00000000892a860] really_probe+0x140/0x680
[c00000000892aefc] driver_probe_device+0x15c/0x200
[c00000000892b63c] device_driver_attach+0xcc/0xe0
[c00000000892b740] __driver_attach+0xf0/0x200
[c000000008926f28] bus_for_each_dev+0xa8/0x130
[c000000008929ce4] driver_attach+0x34/0x50
[c000000008928fc0] bus_add_driver+0x1b0/0x300
[c00000000892c798] driver_register+0x98/0x1a0
[c00000000810eb60] __vio_register_driver+0x80/0xe0
[c0080000190b4a30] ibmvscsi_module_init+0x9c/0xdc [ibmvscsi]
[c0000000080121d0] do_one_initcall+0x60/0x2d0
[c000000008261abc] do_init_module+0x7c/0x320
[c000000008265700] load_module+0x2350/0x25b0
[c000000008265cb4] __do_sys_finit_module+0xd4/0x160
[c000000008031110] system_call_exception+0x150/0x2d0
[c00000000800d35c] system_call_common+0xec/0x278

Fix this be nulling shost->ehandler when the kthread fails to spawn.

Link: https://lore.kernel.org/r/20210701195659.3185475-1-tyreld@linux.ibm.com
Fixes: 66a834d09293 ("scsi: core: Fix error handling of scsi_host_alloc()")
Cc: stable@vger.kernel.org
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>