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

quoted

On Wed, Mar 17, 2021 at 7:37 AM Adrian Hunter [off-list ref] wrote:
On 16/03/21 10:35 pm, Asutosh Das (asd) wrote:
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 [off-list ref] wrote:
On Sat, Mar 6, 2021 at 5:17 PM Alan Stern [off-list ref] 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:
If that is the case, then it is an error in PM not UFS.

A second look at the code around rpm_put_suppliers() does look
potentially racy, since there does not appear to be anything
stopping the runtime_status changing between
spin_unlock_irq(&dev->power.lock) and device_links_read_lock().

Rafael, can you comment?
Indeed, if the device is suspending, changing its PM-runtime status to
RPM_SUSPENDED and dropping its power.lock allows a concurrent
rpm_resume() to run and resume the device before the suppliers can be
suspended.

That's incorrect and has been introduced by commit 44cc89f76464 ("PM:
runtime: Update device status before letting suppliers suspend").

It is probably better to revert that commit and address the original
issue in a different way.

        /*
         * If the device is suspending and the callback has returned success,
         * drop the usage counters of the suppliers that have been reference
         * counted on its resume.
         *
         * Do that if the resume fails too.
         */
        put = dev->power.runtime_status == RPM_SUSPENDING && !retval;
        if (put)
                __update_runtime_status(dev, RPM_SUSPENDED);
        else
                put = get && retval;

        if (put) {
                spin_unlock_irq(&dev->power.lock);

                idx = device_links_read_lock();

fail:
                rpm_put_suppliers(dev);

                device_links_read_unlock(idx);

                spin_lock_irq(&dev->power.lock);
        }

[   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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