Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <cover.1614725302.git.asutoshd@codeaurora.org> <0576d6eae15486740c25767e2d8805f7e94eb79d.1614725302.git.asutoshd@codeaurora.org>
 <85086647-7292-b0a2-d842-290818bd2858@intel.com> <6e98724d-2e75-d1fe-188f-a7010f86c509@codeaurora.org>
 <20210306161616.GC74411@rowland.harvard.edu> <CAJZ5v0ihJe8rNjWRwNic_BQUvKbALNcjx8iiPAh5nxLhOV9duw@mail.gmail.com>
 <CAJZ5v0iJ4yqRTt=mTCC930HULNFNTgvO4f9ToVO6pNz53kxFkw@mail.gmail.com>
 <f1e9b21d-1722-d20b-4bae-df7e6ce50bbc@codeaurora.org> <2bd90336-18a9-9acd-5abb-5b52b27fc535@codeaurora.org>
 <b13086f3-eea1-51a7-2117-579d520f21fc@intel.com> <20cbd52d-7254-3e1c-06a3-712326c99f75@codeaurora.org>
 <c1b38327-fece-4e31-709b-84ec775c6e18@intel.com> <ae871d38-4865-5836-d370-e5f9b7be762c@codeaurora.org>
 <24dfb6fc-5d54-6ee2-9195-26428b7ecf8a@intel.com> <CAJZ5v0iOT4oi8Ez5xgN9LE0E7J=_Vb7G8a-9etmu+QTvQ1j9ew@mail.gmail.com>
 <d9ea43fd-b065-0e6e-07cb-d6ec6ef97bae@codeaurora.org>
In-Reply-To: <d9ea43fd-b065-0e6e-07cb-d6ec6ef97bae@codeaurora.org>
From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Thu, 18 Mar 2021 18:54:37 +0100
Message-ID: <CAJZ5v0iTymqf0yRrfvHoxejzKiZ7hnGH+xXYTZhbDait5ULzTQ@mail.gmail.com>
Subject: Re: [PATCH v10 1/2] scsi: ufs: Enable power management for wlun
To:     "Asutosh Das (asd)" <asutoshd@codeaurora.org>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Bart Van Assche <bvanassche@acm.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>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8BIT
Precedence: bulk

On Thu, Mar 18, 2021 at 6:33 PM Asutosh Das (asd)
<asutoshd@codeaurora.org> wrote:
>
> On 3/18/2021 7:00 AM, Rafael J. Wysocki wrote:
> > On Wed, Mar 17, 2021 at 7:37 AM Adrian Hunter <adrian.hunter@intel.com> 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 <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:
> >>
> >> 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.
> >
> Hello,
> One approach to address the original issue could be to prevent the scsi
> devices from suspending until the probe is completed, perhaps?

I was talking about the original issue that commit 44cc89f76464
attempted to address.

I'm not sure if and how it is related to the issue you have been debugging.