linux-kernel - Re: [PATCH v1] PM-runtime: Check supplier

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Date:   Tue, 2 Aug 2022 21:33:14 +0800
From:   Peter Wang <peter.wang@...iatek.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
CC:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] PM-runtime: Check supplier_preactivated before release
 supplier

On 8/2/22 7:01 PM, Rafael J. Wysocki wrote:
> On Tue, Aug 2, 2022 at 5:19 AM Peter Wang <peter.wang@...iatek.com> wrote:
>>
>>> Hi Rafael,
>>>
>>> Yes, it is very clear!
>>> I miss this important key point that usage_count is always >
>>> rpm_active 1.
>>> I think this patch could work.
>>>
>>> Thanks.
>>> Peter
>>>
>>>
>>>
>>>
>> Hi Rafael,
>>
>> After test with commit ("887371066039011144b4a94af97d9328df6869a2 PM:
>> runtime: Fix supplier device management during consumer probe") past weeks,
>> The supplier still suspend when consumer is active "after"
>> pm_runtime_put_suppliers.
>> Do you have any idea about that?
> Well, this means that the consumer probe doesn't bump up the
> supplier's PM-runtime usage counter as appropriate.
>
> You need to tell me more about what happens during the consumer probe.
> Which driver is this?

Hi Rafael,

I have the same idea with you. But I still don't know how it could happen.

It is upstream ufs driver in scsi system. Here is call flow
do_scan_async (process 1)
     do_scsi_scan_host
         scsi_scan_host_selected
             scsi_scan_channel
                 __scsi_scan_target
                     scsi_probe_and_add_lun
                         scsi_alloc_sdev
                             slave_alloc     -> setup link
                         scsi_add_lun
                             slave_configure    -> enable rpm
                             scsi_sysfs_add_sdev
                                 scsi_autopm_get_device    <- get runtime pm
                                 device_add                <- invoke 
sd_probe in process 2
                                 scsi_autopm_put_device    <- put 
runtime pm, point 1

driver_probe_device (process 2)
     __driver_probe_device
         pm_runtime_get_suppliers
             really_probe
                 sd_probe
                     scsi_autopm_get_device                <- get 
runtime pm, point 2
                     pm_runtime_set_autosuspend_delay    <- set rpm 
delay to 2s
                     scsi_autopm_put_device                <- put 
runtime pm
         pm_runtime_put_suppliers                        <- 
(link->rpm_active = 1)

After process 1 call scsi_autopm_put_device(point 1) let consumer enter 
suspend,
process 2 call scsi_autopm_get_device(point 2) may have chance resume 
consumer but not
bump up the supplier's PM-runtime usage counter as appropriate.

Thanks.
Peter