On Fri, 2009-07-17 at 10:10 +0800, Wu Zhangjin wrote:
> Hi,
>
> On Thu, 2009-07-16 at 13:02 -0400, Alan Stern wrote:
> > On Thu, 16 Jul 2009, Wu Zhangjin wrote:
> >
> > > we can not call msleep() when resuming from STR/Standby: if the
> > > current_state of the pci device is PCI_D3hot, means we are in the
> > > procedure of resuming, in this procedure, we can not re-schedule,
> > > otherwise, there will be a deadlock.
> >
> > I don't understand.
> >
> > First of all, why does current_state == PCI_D3hot mean the system is
> > resuming from sleep? Isn't it possible that the PCI device is going
> > through a runtime resume?
> >
> > Secondly, why will scheduling during a resume cause a deadlock?
>
> Sorry, I'm stupid to make conclusion before describing the problem
> clearly, here is the problem I encountered:
>
> when I enabled SUSPEND=y in linux-2.6.30.1(with relative patches) on a
> loongson-based machine(yeeloong laptop,loongson is mips-compatiable), I
> tried to suspend it via "echo standby > /sys/power/state", with the
> serial port debugging support, I found it enter into the standby mode
> successfully. and then, tried to wake it up via the keyboard interrupt,
> but it stopped at the "Power_up_devices:" of kernel/power/main.c.
>
> here is a short path of this procedure:
>
> suspend_enter:
> ...
> device_power_down
> ...
> arch_suspend_disable_irqs
> ...
> sysdev_suspend
> ...
> suspend_ops->enter (board-specific part)
> ...
> sysdev_resume
> ...
> arch_suspend_enable_irqs
> ...
> device_power_up <-----------------------stop here
> ...
>
> and then I continue to trace it:
>
> device_power_up:
> dpm_power_up:
> list_for_each_entry(dev, &dpm_list, power.entry)
> <<DEBUG>>
> if (dev->power.status > DPM_OFF) {
> int error;
>
> dev->power.status = DPM_OFF;
traced the dev_name(dev) via serial port, and found it with lspci, it
is:
00:09.0 USB Controller: NEC Corporation USB (rev 44)
and the state here is D0, the current_sate is PCI_D3hot.
> error = resume_device_noirq(dev, state);
> if (error)
> pm_dev_err(dev, state, " early", error);
> }
>
> I tried to add prom_putchar() at <<DEBUG>> to print something, and This
> will make it resume from standby mode successfully. seems,
> prom_putchar() have influenced the power.status, and make some devices
> not enter into the condition statement, and make dpm_power_up return
> directly. (this is very weird, not sure why?)
>
> so, I removed the prom_putchar() from <<DEBUG>>, and it stopped at
> resume_device_noirq, here is the following tracing path:
>
> resume_device_noirq:
> --> pm_noirq_op
> --> ops->resume_noirq (dev) <--> pci_pm_resume_noirq:
> --> pci_pm_default_resume_noirq
> --> pci_restore_standard_config
> --> pci_set_power_state
> --> pci_raw_set_power_state
> --> msleep <-----------------------[ stop here]
>
> msleep:
> --> schedule_timeout_uninterruptible
> --> schedule_timeout
> --> ...
> --> __mod_timer
> --> ...
> --> schedule ---> a new scheduling happen and never return
>
> and then I tried to trace schedule(), and even added a prom_putchar() to
> the end of the schedule() function, it output something successfully,
> but never return to schedule_timeout(dead? no keyboard response), seems
> very weird! this is reproductive, perhaps I have missed something here.
>
> so, to avoid this 'weird' situation, I think it's better not to
> re-schedule in the resuming procedure from standby. and here, I can not
> find another condition to judge the resuming procedure from standby, so,
> I use "current_state == PCI_D3hot"(so, my pre-expression is really wrong
> for it maybe not resume from standby as you indicated). and is there
> another condition to judge we are resuming from standby? perhaps this is
> better:
>
> ((current_state == PCI_D3hot) && (state == PCI_D0))
>
> but seems this also can not indicate we are resuming from standby.
>
> Regards,
> Wu Zhangjin
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