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Message-ID: <CAJZ5v0gdg=PUz-j0yd_QJRPmjhZ7pCuRrHt30U60H4QyTHCmdA@mail.gmail.com>
Date: Thu, 1 Dec 2022 20:28:25 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Adrian Hunter <adrian.hunter@...el.com>
Cc: Nitin Rawat <quic_nitirawa@...cinc.com>,
Tushar Nimkar <quic_tnimkar@...cinc.com>,
linux-pm@...r.kernel.org, linux-scsi@...r.kernel.org,
"Rafael J. Wysocki" <rafael@...nel.org>,
linux-arm-msm@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
bjorn.andersson@...nel.org, quic_mkshah@...cinc.com,
quic_lsrao@...cinc.com, bvanassche@....org,
Peter Wang <peter.wang@...iatek.com>
Subject: Re: PM-runtime: supplier looses track of consumer during probe
On Thu, Dec 1, 2022 at 2:10 PM Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> On 29/11/22 18:56, Nitin Rawat wrote:
> > Hi Adrian,
> >
> > On 11/21/2022 11:38 AM, Tushar Nimkar wrote:
> >> Hi Adrian,
> >>
> >> On 11/18/2022 8:25 PM, Adrian Hunter wrote:
> >>> On 4/11/22 11:19, Tushar Nimkar wrote:
> >>>> Hi linux-pm/linux-scsi,
> >>
> >>>>> Process -1
> >>>>> ufshcd_async_scan context (process 1)
> >>>>> scsi_autopm_put_device() //0:0:0:0
> >>>
> >>> I am having trouble following your description. What function is calling
> >>> scsi_autopm_put_device() here?
> >>>
> >> Below is flow which calls scsi_autopm_put_device()
> >> Process -1
> >> ufshcd_async_scan()
> >> scsi_probe_and_add_lun()
> >> scsi_add_lun()
> >> slave_configure()
> >> scsi_sysfs_add_sdev()
> >> scsi_autopm_get_device()
> >> device_add() <- invoked [Process 2] sd_probe()
> >> scsi_autopm_put_device()
> >>
> >>>>> pm_runtime_put_sync()
> >>>>> __pm_runtime_idle()
> >>>>> rpm_idle() -- RPM_GET_PUT(4)
> >>>>> __rpm_callback
> >>>>> scsi_runtime_idle()
> >>>>> pm_runtime_mark_last_busy()
> >>>>> pm_runtime_autosuspend() --[A]
> >>>>> rpm_suspend() -- RPM_AUTO(8)
> >>>>> pm_runtime_autosuspend_expiration() use_autosuspend is false return 0 --- [B]
> >>>>> __update_runtime_status to RPM_SUSPENDING
> >>>>> __rpm_callback()
> >>>>> __rpm_put_suppliers(dev, false)
> >>>>> __update_runtime_status to RPM_SUSPENDED
> >>>>> rpm_suspend_suppliers()
> >>>>> rpm_idle() for supplier -- RPM_ASYNC(1) return (-EAGAIN) [ Other consumer active for supplier]
> >>>>> rpm_suspend() – END with return=0
> >>>>> scsi_runtime_idle() END return (-EBUSY) always.
> >>>
> >>> Not following here either. Which device is EBUSY and why?
> >>
> >> scsi_runtime_idle() return -EBUSY always [3]
> >> Storage/scsi team can better explain -EBUSY implementation.
> >
> > EBUSY is returned from below code for consumer dev 0:0:0:0.
> > scsi_runtime_idle is called from scsi_autopm_put_device which inturn is called from ufshcd_async_scan (Process 1 as per above call stack)
> > static int scsi_runtime_idle(struct device *dev)
> > {
> > :
> >
> > if (scsi_is_sdev_device(dev)) {
> > pm_runtime_mark_last_busy(dev);
> > pm_runtime_autosuspend(dev);
> > return -EBUSY; ---> EBUSY returned from here.
> > }
> >
> >
> > }
> >
> >>
> >> [3] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/scsi/scsi_pm.c?h=next-20221118#n210
> >>
> >>
> >>>>>
> >>>>> [1]: https://lore.kernel.org/lkml/4748074.GXAFRqVoOG@kreacher/T/
> >>>>> [2]: https://lkml.org/lkml/2022/10/12/259
>
> It looks to me like __rpm_callback() makes assumptions about
> dev->power.runtime_status that are not necessarily true because
> dev->power.lock is dropped.
Well, this happens because rpm_idle() calls __rpm_callback() and
allows it to run concurrently with rpm_suspend() and rpm_resume(), so
one of them may change runtime_status to RPM_SUSPENDING or
RPM_RESUMING while __rpm_callback() is running.
It is somewhat questionable whether or not this should be allowed to
happen, but since it is generally allowed to suspend the device from
its .runtime_idle callback, there is not too much that can be done
about it.
> AFAICT the intention of the code would be fulfilled by instead using the status as it was before
> the lock was dropped.
That's correct, so the patch should help, but it also needs to remove
the comment stating that the runtime status cannot change when
__rpm_callback() is running, which is clearly incorrect.
> Consequently, perhaps you could try this:
>
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index b52049098d4e..3cf9abc3b2c2 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -365,6 +365,7 @@ static int __rpm_callback(int (*cb)(struct device *), struct device *dev)
> {
> int retval = 0, idx;
> bool use_links = dev->power.links_count > 0;
> + enum rpm_status runtime_status = dev->power.runtime_status;
>
> if (dev->power.irq_safe) {
> spin_unlock(&dev->power.lock);
> @@ -378,7 +379,7 @@ static int __rpm_callback(int (*cb)(struct device *), struct device *dev)
> * routine returns, so it is safe to read the status outside of
> * the lock.
> */
> - if (use_links && dev->power.runtime_status == RPM_RESUMING) {
> + if (use_links && runtime_status == RPM_RESUMING) {
> idx = device_links_read_lock();
>
> retval = rpm_get_suppliers(dev);
> @@ -405,8 +406,8 @@ static int __rpm_callback(int (*cb)(struct device *), struct device *dev)
> * Do that if resume fails too.
> */
> if (use_links
> - && ((dev->power.runtime_status == RPM_SUSPENDING && !retval)
> - || (dev->power.runtime_status == RPM_RESUMING && retval))) {
> + && ((runtime_status == RPM_SUSPENDING && !retval)
> + || (runtime_status == RPM_RESUMING && retval))) {
> idx = device_links_read_lock();
>
> __rpm_put_suppliers(dev, false);
>
>
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