Date:   Sun, 14 Mar 2021 11:11:04 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     "Asutosh Das (asd)" <asutoshd@...eaurora.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Bart Van Assche <bvanassche@....org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>, cang@...eaurora.org,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "open list:TARGET SUBSYSTEM" <linux-scsi@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Kiwoong Kim <kwmad.kim@...sung.com>,
        Bean Huo <beanhuo@...ron.com>,
        Lee Jones <lee.jones@...aro.org>,
        Wei Yongjun <weiyongjun1@...wei.com>,
        Dinghao Liu <dinghao.liu@....edu.cn>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Tomas Winkler <tomas.winkler@...el.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Satya Tangirala <satyat@...gle.com>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/SAMSUNG S3C, S5P AND EXYNOS ARM ARCHITECTURES" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/SAMSUNG S3C, S5P AND EXYNOS ARM ARCHITECTURES" 
        <linux-samsung-soc@...r.kernel.org>,
        "moderated list:UNIVERSAL FLASH STORAGE HOST CONTROLLER DRIVER..." 
        <linux-mediatek@...ts.infradead.org>,
        Linux-PM mailing list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v10 1/2] scsi: ufs: Enable power management for wlun

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@...nel.org> wrote:
>>>>
>>>> On Sat, Mar 6, 2021 at 5:17 PM Alan Stern <stern@...land.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/@...n - 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?

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.

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.


> 
> 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/@...t/@...ian) have any thoughts on this.
> 
> Thanks,
> -asd
> 

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