Re: [PATCH v10 1/2] scsi: ufs: Enable power management for wlun

Asutosh Das (asd)
2021-03-16T20:36:47Z

On 3/16/2021 12:48 AM, Adrian Hunter wrote:
> On 16/03/21 12:22 am, Asutosh Das (asd) wrote:
>> On 3/14/2021 1:11 AM, Adrian Hunter wrote:
>>> On 10/03/21 5:04 am, Asutosh Das (asd) wrote:
>>>> On 3/9/2021 7:56 AM, Asutosh Das (asd) wrote:
>>>>> On 3/8/2021 9:17 AM, Rafael J. Wysocki wrote:
>>>>>> On Mon, Mar 8, 2021 at 5:21 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>>>>>>>
>>>>>>> On Sat, Mar 6, 2021 at 5:17 PM Alan Stern <stern@rowland.harvard.edu> wrote:
>>>>>>>>
>>>>>>>> On Fri, Mar 05, 2021 at 06:54:24PM -0800, Asutosh Das (asd) wrote:
>>>>>>>>
>>>>>>>>> Now during my testing I see a weird issue sometimes (1 in 7).
>>>>>>>>> Scenario - bootups
>>>>>>>>>
>>>>>>>>> Issue:
>>>>>>>>> The supplier 'ufs_device_wlun 0:0:0:49488' goes into runtime suspend even
>>>>>>>>> when one/more of its consumers are in RPM_ACTIVE state.
>>>>>>>>>
>>>>>>>>> *Log:
>>>>>>>>> [   10.056379][  T206] sd 0:0:0:1: [sdb] Synchronizing SCSI cache
>>>>>>>>> [   10.062497][  T113] sd 0:0:0:5: [sdf] Synchronizing SCSI cache
>>>>>>>>> [   10.356600][   T32] sd 0:0:0:7: [sdh] Synchronizing SCSI cache
>>>>>>>>> [   10.362944][  T174] sd 0:0:0:3: [sdd] Synchronizing SCSI cache
>>>>>>>>> [   10.696627][   T83] sd 0:0:0:2: [sdc] Synchronizing SCSI cache
>>>>>>>>> [   10.704562][  T170] sd 0:0:0:6: [sdg] Synchronizing SCSI cache
>>>>>>>>> [   10.980602][    T5] sd 0:0:0:0: [sda] Synchronizing SCSI cache
>>>>>>>>>
>>>>>>>>> /** Printing all the consumer nodes of supplier **/
>>>>>>>>> [   10.987327][    T5] ufs_device_wlun 0:0:0:49488: usage-count @ suspend: 0
>>>>>>>>> <-- this is the usage_count
>>>>>>>>> [   10.994440][    T5] ufs_rpmb_wlun 0:0:0:49476: PM state - 2
>>>>>>>>> [   11.000402][    T5] scsi 0:0:0:49456: PM state - 2
>>>>>>>>> [   11.005453][    T5] sd 0:0:0:0: PM state - 2
>>>>>>>>> [   11.009958][    T5] sd 0:0:0:1: PM state - 2
>>>>>>>>> [   11.014469][    T5] sd 0:0:0:2: PM state - 2
>>>>>>>>> [   11.019072][    T5] sd 0:0:0:3: PM state - 2
>>>>>>>>> [   11.023595][    T5] sd 0:0:0:4: PM state - 0 << RPM_ACTIVE
>>>>>>>>> [   11.353298][    T5] sd 0:0:0:5: PM state - 2
>>>>>>>>> [   11.357726][    T5] sd 0:0:0:6: PM state - 2
>>>>>>>>> [   11.362155][    T5] sd 0:0:0:7: PM state - 2
>>>>>>>>> [   11.366584][    T5] ufshcd-qcom 1d84000.ufshc: __ufshcd_wl_suspend - 8709
>>>>>>>>> [   11.374366][    T5] ufs_device_wlun 0:0:0:49488: __ufshcd_wl_suspend -
>>>>>>>>> (0) has rpm_active flags
>>>>>>>
>>>>>>> Do you mean that rpm_active of the link between the consumer and the
>>>>>>> supplier is greater than 0 at this point and the consumer is
>>>>>>
>>>>>> I mean is rpm_active of the link greater than 1 (because 1 means "no
>>>>>> active references to the supplier")?
>>>>> Hi Rafael:
>>>>> No - it is not greater than 1.
>>>>>
>>>>> I'm trying to understand what's going on in it; will update when I've something.
>>>>>
>>>>>>
>>>>>>> RPM_ACTIVE, but the supplier suspends successfully nevertheless?
>>>>>>>
>>>>>>>>> [   11.383376][    T5] ufs_device_wlun 0:0:0:49488:
>>>>>>>>> ufshcd_wl_runtime_suspend <-- Supplier suspends fine.
>>>>>>>>> [   12.977318][  T174] sd 0:0:0:4: [sde] Synchronizing SCSI cache
>>>>>>>>>
>>>>>>>>> And the the suspend of sde is stuck now:
>>>>>>>>> schedule+0x9c/0xe0
>>>>>>>>> schedule_timeout+0x40/0x128
>>>>>>>>> io_schedule_timeout+0x44/0x68
>>>>>>>>> wait_for_common_io+0x7c/0x100
>>>>>>>>> wait_for_completion_io+0x14/0x20
>>>>>>>>> blk_execute_rq+0x90/0xcc
>>>>>>>>> __scsi_execute+0x104/0x1c4
>>>>>>>>> sd_sync_cache+0xf8/0x2a0
>>>>>>>>> sd_suspend_common+0x74/0x11c
>>>>>>>>> sd_suspend_runtime+0x14/0x20
>>>>>>>>> scsi_runtime_suspend+0x64/0x94
>>>>>>>>> __rpm_callback+0x80/0x2a4
>>>>>>>>> rpm_suspend+0x308/0x614
>>>>>>>>> pm_runtime_work+0x98/0xa8
>>>>>>>>>
>>>>>>>>> I added 'DL_FLAG_RPM_ACTIVE' while creating links.
>>>>>>>>>         if (hba->sdev_ufs_device) {
>>>>>>>>>                 link = device_link_add(&sdev->sdev_gendev,
>>>>>>>>>                                     &hba->sdev_ufs_device->sdev_gendev,
>>>>>>>>>                                    DL_FLAG_PM_RUNTIME|DL_FLAG_RPM_ACTIVE);
>>>>>>>>> I didn't expect this to resolve the issue anyway and it didn't.
>>>>>>>>>
>>>>>>>>> Another interesting point here is when I resume any of the above suspended
>>>>>>>>> consumers, it all goes back to normal, which is kind of expected. I tried
>>>>>>>>> resuming the consumer and the supplier is resumed and the supplier is
>>>>>>>>> suspended when all the consumers are suspended.
>>>>>>>>>
>>>>>>>>> Any pointers on this issue please?
>>>>>>>>>
>>>>>>>>> @Bart/@Alan - Do you've any pointers please?
>>>>>>>>
>>>>>>>> It's very noticeable that although you seem to have isolated a bug in
>>>>>>>> the power management subsystem (supplier goes into runtime suspend
>>>>>>>> even when one of its consumers is still active), you did not CC the
>>>>>>>> power management maintainer or mailing list.
>>>>>>>>
>>>>>>>> I have added the appropriate CC's.
>>>>>>>
>>>>>>> Thanks Alan!
>>>>>
>>>>>
>>>>
>>>> Hello
>>>> I & Can (thanks CanG) debugged this further:
>>>>
>>>> Looks like this issue can occur if the sd probe is asynchronous.
>>>>
>>>> Essentially, the sd_probe() is done asynchronously and driver_probe_device() invokes pm_runtime_get_suppliers() before invoking sd_probe().
>>>>
>>>> But scsi_probe_and_add_lun() runs in a separate context.
>>>> So the scsi_autopm_put_device() invoked from scsi_scan_host() context reduces the link->rpm_active to 1. And sd_probe() invokes scsi_autopm_put_device() and starts a timer. And then driver_probe_device() invoked from __device_attach_async_helper context reduces the link->rpm_active to 1 thus enabling the supplier to suspend before the consumer suspends.
>>>>
>>>> So if:
>>>> Context T1:
>>>> [1] scsi_probe_and_add_lun()
>>>> [2]    |- scsi_autopm_put_device() - reduce the link->rpm_active to 1
>>>>
>>>> Context T2:
>>>> __device_attach_async_helper()
>>>>      |- driver_probe_device()
>>>>          |- sd_probe()
>>>> In between [1] and [2] say, driver_probe_device() -> sd_probe() is invoked in a separate context from __device_attach_async_helper().
>>>> The driver_probe_device() -> pm_runtime_get_suppliers() but [2] would reduce link->rpm_active to 1.
>>>> Then sd_probe() would invoke rpm_resume() and proceed as is.
>>>> When sd_probe() invokes scsi_autopm_put_device() it'd start a timer, dev->power.timer_autosuspends = 1.
>>>>
>>>> Now then, pm_runtime_put_suppliers() is invoked from driver_probe_device() and that makes the link->rpm_active = 1.
>>>> But by now, the corresponding 'sd dev' (consumer) usage_count = 0, state = RPM_ACTIVE and link->rpm_active = 1.
>>>> At this point of time, all other 'sd dev' (consumers) _may_ be suspended or active but would have the link->rpm_active = 1.
>>>
>>> Is this with DL_FLAG_RPM_ACTIVE?  In that case, wouldn't active
>>> consumers have link->rpm_active = 2 and also have incremented
>>> the supplier's usage_count?

Yes this is with DL_FLAG_RPM_ACTIVE.

Please let me share a log here:
BEF means - Before, AFT means After.

[ 6.843445][ T7] scsi 0:0:0:4: [UFSDBG]: ufshcd_setup_links:4779:
supp: usage_cnt: 3 Link - 0:0:0:49488 link-rpm_active: 2 avail_luns: 5
[ 6.892545][ T7] scsi 0:0:0:4: pm_runtime_get_suppliers:
(0:0:0:49488): supp: usage_count: 5 rpm_active: 4

In the above log, T7 is the context in which this scsi device is being
added - scsi_sysfs_add_sdev()

[ 6.931846][ T7] ufs_rpmb_wlun 0:0:0:4: [UFSDBG]:
ufshcd_rpmb_probe:9692: invoked
[ 6.941246][ T7] scsi 0:0:0:4: pm_runtime_put_suppliers: rpm_active: 4

[ 6.941246][ T7] scsi 0:0:0:4: pm_runtime_put_suppliers:
(0:0:0:49488) [BEF] usage_count: 5
[ 6.941247][ T7] scsi 0:0:0:4: pm_runtime_put_suppliers:
(0:0:0:49488) [AFT] usage_count: 4 rpm_active: 3

[ 6.941267][ T7] scsi 0:0:0:4: rpm_put_suppliers: [BEF] Supp
(0:0:0:49488) usage_count: 4 rpm_active: 3

------ T196 Context comes in while T7 is running ----------
[ 6.941466][ T196] scsi 0:0:0:4: pm_runtime_get_suppliers:
(0:0:0:49488): supp: usage_count: 5 rpm_active: 4
--------------------------------------------------------------

[ 7.788397][ T7] scsi 0:0:0:4: rpm_put_suppliers: [AFT] Supp
(0:0:0:49488) usage_count: 2 rpm_active: 1

--

T196 is the context in which sd_probe() is invoked for this scsi device.

[ 7.974410][ T196] sd 0:0:0:4: [sde] Attached SCSI disk
[ 7.984188][ T196] sd 0:0:0:4: pm_runtime_put_suppliers: rpm_active: 2
[ 7.998424][ T196] sd 0:0:0:4: pm_runtime_put_suppliers:
(0:0:0:49488) [BEF] usage_count: 4
[ 8.017320][ T196] sd 0:0:0:4: pm_runtime_put_suppliers:
(0:0:0:49488) [AFT] usage_count: 1 rpm_active: 1

The reference to the link is released after sd_probe() is completed.
At this point, the rpm_active should be 2. And the rpm_active should
become 1 when sd 0:0:0:4 actually suspends. But at the end of sd_probe()
the suspend is only scheduled. However the supplier is now free to suspend.

In this log, the usage_count of supplier becomes 0 here:
[ 11.963885][ T117] sd 0:0:0:7: rpm_put_suppliers: [BEF] Supp
(0:0:0:49488) usage_count: 1 rpm_active: 2
[ 11.973821][ T117] sd 0:0:0:7: rpm_put_suppliers: [AFT] Supp
(0:0:0:49488) usage_count: 0 rpm_active: 1

However, the consumer sd 0:0:0:4 is still active but has released the
reference to the supplier:
[ 12.002792][ T117] scsi 0:0:0:49456: rpm_status - 2
[ 12.002806][ T117] sd 0:0:0:0: rpm_status - 2
[ 12.002834][ T117] sd 0:0:0:1: rpm_status - 2
[ 12.017730][ T117] sd 0:0:0:2: rpm_status - 2
[ 12.041317][ T117] sd 0:0:0:3: rpm_status - 2
[ 12.045953][ T117] sd 0:0:0:4: rpm_status - 0

And sd 0:0:0:4 tries to suspend here:
[ 15.465914][ T117] sd 0:0:0:4: [sde] Synchronizing SCSI cache

>>>
>>> Another outstanding issue that comes to mind, is to ensure
>>> hba->sdev_ufs_device does not runtime suspend before it is probed.
>>> I suggest changing ufshcd_slave_configure() so it does not set
>>> sdev->rpm_autosuspend for hba->sdev_ufs_device, and instead do
>>> pm_runtime_allow / pm_runtime_forbid() in ufshcd_wl_probe() /
>>> ufshcd_wl_remove() respectively.
>>>
If pm_runtime_allow() is invoked from ufshcd_wl_probe() it'd invoke
runtime_suspend on hba->sdev_ufs_device before exiting
scsi_sysfs_add_sdev(). So I think pm_runtime_allow() should be invoked
in ufshcd_scsi_add_wlus().

>>> However we still want to stop hba->sdev_ufs_device runtime
>>> suspending while consumers are being added.  With that in mind,
>>> I would expect pm_runtime_get_noresume(&hba->sdev_ufs_device->sdev_gendev)
>>> in ufshcd_scsi_add_wlus() to come *before*
>>> ufshcd_blk_pm_runtime_init(hba->sdev_ufs_device).  In fact, it would
>>> be more logical to make it, pm_runtime_get_sync() since we require
>>> hba->sdev_ufs_device to be active at that point.
>>>
Correct, scsi_autopm_get_device(hba->sdev_ufs_device) should be invoked
before ufshcd_blk_pm_runtime_init(hba->sdev_ufs_device).
Now a corresponding scsi_autopm_put_device(hba->sdev_ufs_device) is
invoked after the consumers are added in ufshcd_setup_links().
Even then I think this issue would still pop up.

>>>
>>
>> Hi Adrian,
>> I think the v11 that I pushed can handle this.
>> runtime-suspend is forbidden at probe and is re-enabled after probe is done. Please take a look and let me know if I'm missing something.
>
> If the PM APIs are being used correctly, the usage and active
> counts should never be wrong. If they were, then that would
> be an issue for the PM framework.
>It is more likely that I'm using it incorrectly :).

> However, it is hard to tell what the issues are until all the
> UFS driver changes have been completed, such as the ones I
> suggested above above.
>
Ok, understood.

> v11 could be hiding issues rather than fixing them.
>
Based on the logs, in v11, I tried to forbid any runtime-suspend until
sd_probe() is done.
I could be misunderstanding the whole thing though.

Having said that, I will make the changes as per your suggestions and
push a v12. I will test with v12 as well and see if this issue is seen.

>>
>>>>
>>>> Since the supplier has 0 auto-suspend delay, it now suspends!
>>>>
>>>>
>>>> Context [T1]
>>>> Call trace:
>>>> dump_backtrace+0x0/0x1d4
>>>> show_stack+0x18/0x24
>>>> dump_stack+0xc4/0x144
>>>> __pm_runtime_idle+0xb4/0x184
>>>> scsi_autopm_put_device+0x18/0x24
>>>> scsi_sysfs_add_sdev+0x26c/0x278
>>>> scsi_probe_and_add_lun+0xbac/0xd48
>>>> __scsi_scan_target+0x38c/0x510
>>>> scsi_scan_host_selected+0x14c/0x1e4
>>>> scsi_scan_host+0x1e0/0x228
>>>> ufshcd_async_scan+0x39c/0x408
>>>> async_run_entry_fn+0x48/0x128
>>>> process_one_work+0x1f0/0x470
>>>> worker_thread+0x26c/0x4c8
>>>> kthread+0x13c/0x320
>>>> ret_from_fork+0x10/0x18
>>>>
>>>>
>>>> Context [T2]
>>>> Call trace:
>>>> dump_backtrace+0x0/0x1d4
>>>> show_stack+0x18/0x24
>>>> dump_stack+0xc4/0x144
>>>> rpm_get_suppliers+0x48/0x1ac
>>>> __rpm_callback+0x58/0x12c
>>>> rpm_resume+0x3a4/0x618
>>>> __pm_runtime_resume+0x50/0x80
>>>> scsi_autopm_get_device+0x20/0x54
>>>> sd_probe+0x40/0x3d0
>>>> really_probe+0x1bc/0x4a0
>>>> driver_probe_device+0x84/0xf0
>>>> __device_attach_driver+0x114/0x138
>>>> bus_for_each_drv+0x84/0xd0
>>>> __device_attach_async_helper+0x7c/0xf0
>>>> async_run_entry_fn+0x48/0x128
>>>> process_one_work+0x1f0/0x470
>>>> worker_thread+0x26c/0x4c8
>>>> kthread+0x13c/0x320
>>>> ret_from_fork+0x10/0x18
>>>>
>>>> Below prints show how link->rpm_active becomes 1 for sd 0:0:0:4
>>>> [    7.574654][  T212] Call trace:
>>>> [    7.574657][  T212]  dump_backtrace+0x0/0x1d4
>>>> [    7.574661][  T212]  show_stack+0x18/0x24
>>>> [    7.574665][  T212]  dump_stack+0xc4/0x144
>>>> [    7.574668][  T212]  __pm_runtime_idle+0xb4/0x184
>>>> [    7.574671][  T212]  scsi_autopm_put_device+0x18/0x24
>>>> [    7.574675][  T212]  sd_probe+0x314/0x3d0
>>>> [    7.574677][  T212]  really_probe+0x1bc/0x4a0
>>>> [    7.574680][  T212]  driver_probe_device+0x84/0xf0
>>>> [    7.574683][  T212]  __device_attach_driver+0x114/0x138
>>>> [    7.574686][  T212]  bus_for_each_drv+0x84/0xd0
>>>> [    7.574689][  T212]  __device_attach_async_helper+0x7c/0xf0
>>>> [    7.574692][  T212]  async_run_entry_fn+0x48/0x128
>>>> [    7.574695][  T212]  process_one_work+0x1f0/0x470
>>>> [    7.574698][  T212]  worker_thread+0x26c/0x4c8
>>>> [    7.574700][  T212]  kthread+0x13c/0x320
>>>> [    7.574703][  T212]  ret_from_fork+0x10/0x18
>>>> [    7.574706][  T212] sd 0:0:0:4: scsi_runtime_idle
>>>> [    7.574712][  T212] sd 0:0:0:4: __pm_runtime_idle: aft: [UFSDBG]: pwr.timer_autosuspends: 1 pwr.request_pending: 0 retval: -16 pwr.request: 0 usage_count: 0 rpm_status: 0 link-rpm_active:2
>>>> [    7.574715][  T212] sd 0:0:0:4: sd_probe: [UFSDBG]: Exit
>>>> [    7.574738][  T212] sd 0:0:0:4: __pm_runtime_idle: b4: [UFSDBG]: pwr.request: 0 usage_count: 0 rpm_status: 0 link-rpm_active:2
>>>>
>>>> [    7.574752][  T212] Workqueue: events_unbound async_run_entry_fn
>>>> [    7.574754][  T212] Call trace:
>>>> [    7.574758][  T212]  dump_backtrace+0x0/0x1d4
>>>> [    7.574761][  T212]  show_stack+0x18/0x24
>>>> [    7.574765][  T212]  dump_stack+0xc4/0x144
>>>> [    7.574767][  T212]  __pm_runtime_idle+0xb4/0x184
>>>> [    7.574770][  T212]  driver_probe_device+0x94/0xf0
>>>> [    7.574773][  T212]  __device_attach_driver+0x114/0x138
>>>> [    7.574775][  T212]  bus_for_each_drv+0x84/0xd0
>>>> [    7.574778][  T212]  __device_attach_async_helper+0x7c/0xf0
>>>> [    7.574781][  T212]  async_run_entry_fn+0x48/0x128
>>>> [    7.574783][  T212]  process_one_work+0x1f0/0x470
>>>> [    7.574786][  T212]  worker_thread+0x26c/0x4c8
>>>> [    7.574788][  T212]  kthread+0x13c/0x320
>>>> [    7.574791][  T212]  ret_from_fork+0x10/0x18
>>>> [    7.574848][   T80] sd 0:0:0:4: scsi_runtime_idle
>>>> [    7.574858][  T212] sd 0:0:0:4: __pm_runtime_idle: aft: [UFSDBG]: pwr.timer_autosuspends: 1 pwr.request_pending: 0 retval: 0 pwr.request: 0 usage_count: 0 rpm_status: 0 link-rpm_active:2
>>>> [    7.574863][  T212] sd 0:0:0:4: pm_runtime_put_suppliers: [UFSDBG]: rpm_status: 0 link-rpm_active:1
>>>> [    7.574866][  T212] sd 0:0:0:4: async probe completed
>>>> [    7.574870][  T212] sd 0:0:0:4: __pm_runtime_idle: b4: [UFSDBG]: pwr.request: 0 usage_count: 0 rpm_status: 0 link-rpm_active:1
>>>>
>>>>
>>>> So, from the above it looks like when async probe is enabled this is a possibility.
>>>>
>>>> I don't see a way around this. Please let me know if you (@Alan/@Bart/@Adrian) have any thoughts on this.
>>>>
>>>> Thanks,
>>>> -asd
>>>>
>>>
>>
>>
>

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