From: "Asutosh Das (asd)" <asutoshd@codeaurora.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Bart Van Assche <bvanassche@acm.org>,
Adrian Hunter <adrian.hunter@intel.com>,
"Rafael J. Wysocki" <rafael@kernel.org>,
cang@codeaurora.org,
"Martin K. Petersen" <martin.petersen@oracle.com>,
"open list:TARGET SUBSYSTEM" <linux-scsi@vger.kernel.org>,
linux-arm-msm <linux-arm-msm@vger.kernel.org>,
Alim Akhtar <alim.akhtar@samsung.com>,
Avri Altman <avri.altman@wdc.com>,
"James E.J. Bottomley" <jejb@linux.ibm.com>,
Krzysztof Kozlowski <krzk@kernel.org>,
Stanley Chu <stanley.chu@mediatek.com>,
Andy Gross <agross@kernel.org>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
Kiwoong Kim <kwmad.kim@samsung.com>,
Bean Huo <beanhuo@micron.com>, Lee Jones <lee.jones@linaro.org>,
Wei Yongjun <weiyongjun1@huawei.com>,
Dinghao Liu <dinghao.liu@zju.edu.cn>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
Tomas Winkler <tomas.winkler@intel.com>,
Jaegeuk Kim <jaegeuk@kernel.org>,
Satya Tangirala <satyat@google.com>,
open list <linux-kernel@vger.kernel.org>,
"moderated list:ARM/SAMSUNG S3C,
S5P AND EXYNOS ARM ARCHITECTURES"
<linux-arm-kernel@lists.infradead.org>,
"open list:ARM/SAMSUNG S3C,
S5P AND EXYNOS ARM ARCHITECTURES"
<linux-samsung-soc@vger.kernel.org>,
"moderated list:UNIVERSAL FLASH STORAGE HOST CONTROLLER
DRIVER..." <linux-mediatek@lists.infradead.org>,
Linux-PM mailing list <linux-pm@vger.kernel.org>
Subject: Re: [PATCH v10 1/2] scsi: ufs: Enable power management for wlun
Date: Wed, 10 Mar 2021 08:39:51 -0800 [thread overview]
Message-ID: <a89ad647-6c0c-b45e-cff3-a205bed034cf@codeaurora.org> (raw)
In-Reply-To: <20210310162730.GB221857@rowland.harvard.edu>
On 3/10/2021 8:27 AM, Alan Stern wrote:
> On Tue, Mar 09, 2021 at 08:04:53PM -0800, Asutosh Das (asd) wrote:
>> On 3/9/2021 7:14 PM, Alan Stern wrote:
>>> On Tue, Mar 09, 2021 at 07:04:34PM -0800, Asutosh Das (asd) wrote:
>>>> 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.
>>>
>>>> I don't see a way around this. Please let me know if you
>>>> (@Alan/@Bart/@Adrian) have any thoughts on this.
>>>
>>> How about changing the SCSI core so that it does a runtime_get before
>>> starting an async probe, and the async probe routine does a
>>> runtime_put when it is finished? In other words, don't allow a device
>>> to go into runtime suspend while it is waiting to be probed.
>>>
>>> I don't think that would be too intrusive.
>>>
>>> Alan Stern
>>>
>>
>> Hi Alan
>> Thanks for the suggestion.
>>
>> Am trying to understand:
>>
>> Do you mean something like this:
>>
>> int scsi_sysfs_add_sdev(struct scsi_device *sdev)
>> {
>>
>> scsi_autopm_get_device(sdev);
>> pm_runtime_get_noresume(&sdev->sdev_gendev);
>> [...]
>> scsi_autopm_put_device(sdev);
>> [...]
>> }
>>
>> static int sd_probe(struct device *dev)
>> {
>> [...]
>> pm_runtime_put_noidle(dev);
>> scsi_autopm_put_device(sdp);
>> [...]
>> }
>>
>> This may work (I'm limited by my imagination in scsi layer :) ).
>
> I'm not sure about this. To be honest, I did not read the entirety of
> your last message; it had way too much detail. THere's a time and place
> for that, but when you're brainstorming to figure out the underlying
> cause of a problem and come up with a strategy to fix it, you want to
> concentrate on the overall picture, not the details.
>
> As I understand the situation, you've get a SCSI target with multiple
> logical units, let's say A and B, and you need to make sure that A never
> goes into runtime suspend unless B is already suspended. In other
> words, B always has to suspend before A and resume after A.
>
> To do this, you register a device link with A as the supplier and B as
> the consumer. Then the PM core takes care of the ordering for you.
>
> But I don't understand when you set up the device link. If the timing
> is wrong then, thanks to async SCSI probing, you may have a situation
> where A is registered before B and before the link is set up. Then
> there's temporarily nothing to stop A from suspending before B.
>
> You also need to prevent each device from suspending before it is
> probed. That's the easy part I was trying to address before (although
> it may not be so easy if the drivers are in loadable modules and not
> present in the kernel).
>
> You need to think through these issues before proposing actual changes.
>
>> But the pm_runtime_put_noidle() would have to be added to all registered
>> scsi_driver{}, perhaps? Or may be I can check for sdp->type?
>
> Like this; it's too early to worry about this sort of thing.
>
> Alan Stern
>
Hi Alan
Thanks. Understood.
I will check the details and see if I can come up with something.
I'll propose an alternate fix otherwise and drop this change altogether.
Thanks!
-asd
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
Linux Foundation Collaborative Project
next prev parent reply other threads:[~2021-03-10 16:40 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-02 22:52 [PATCH v10 0/2] Enable power management for ufs wlun Asutosh Das
2021-03-02 22:52 ` [PATCH v10 1/2] scsi: ufs: Enable power management for wlun Asutosh Das
2021-03-04 15:35 ` Adrian Hunter
2021-03-06 2:54 ` Asutosh Das (asd)
2021-03-06 16:16 ` Alan Stern
2021-03-08 16:21 ` Rafael J. Wysocki
2021-03-08 17:17 ` Rafael J. Wysocki
2021-03-09 15:56 ` Asutosh Das (asd)
2021-03-10 3:04 ` Asutosh Das (asd)
2021-03-10 3:14 ` Alan Stern
2021-03-10 4:04 ` Asutosh Das (asd)
2021-03-10 16:27 ` Alan Stern
2021-03-10 16:39 ` Asutosh Das (asd) [this message]
2021-03-14 9:11 ` Adrian Hunter
2021-03-15 22:22 ` Asutosh Das (asd)
2021-03-16 7:48 ` Adrian Hunter
2021-03-16 20:35 ` Asutosh Das (asd)
2021-03-17 6:37 ` Adrian Hunter
2021-03-18 14:00 ` Rafael J. Wysocki
2021-03-18 17:27 ` Asutosh Das (asd)
2021-03-18 17:54 ` Rafael J. Wysocki
2021-03-18 17:58 ` Asutosh Das (asd)
2021-03-18 19:16 ` Adrian Hunter
2021-03-19 0:40 ` Asutosh Das (asd)
2021-03-02 22:52 ` [PATCH v10 2/2] ufs: sysfs: Resume the proper scsi device Asutosh Das
2021-03-03 4:31 ` Can Guo
2021-03-04 7:45 ` Adrian Hunter
2021-03-04 15:32 ` Asutosh Das
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