linux-kernel - Re: [PATCH] PCI: PM: Avoid possible suspend-to-idle issue

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Message-Id: <527F9B70-68AC-4CD4-A3C2-576EA09187DD@canonical.com>
Date:   Tue, 11 Jun 2019 16:39:44 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Keith Busch <kbusch@...nel.org>
Subject: Re: [PATCH] PCI: PM: Avoid possible suspend-to-idle issue

Hi Rafael,

at 19:02, Rafael J. Wysocki <rjw@...ysocki.net> wrote:

> On Friday, May 17, 2019 11:08:50 AM CEST Rafael J. Wysocki wrote:
>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>
>> If a PCI driver leaves the device handled by it in D0 and calls
>> pci_save_state() on the device in its ->suspend() or ->suspend_late()
>> callback, it can expect the device to stay in D0 over the whole
>> s2idle cycle.  However, that may not be the case if there is a
>> spurious wakeup while the system is suspended, because in that case
>> pci_pm_suspend_noirq() will run again after pci_pm_resume_noirq()
>> which calls pci_restore_state(), via pci_pm_default_resume_early(),
>> so state_saved is cleared and the second iteration of
>> pci_pm_suspend_noirq() will invoke pci_prepare_to_sleep() which
>> may change the power state of the device.
>>
>> To avoid that, add a new internal flag, skip_bus_pm, that will be set
>> by pci_pm_suspend_noirq() when it runs for the first time during the
>> given system suspend-resume cycle if the state of the device has
>> been saved already and the device is still in D0.  Setting that flag
>> will cause the next iterations of pci_pm_suspend_noirq() to set
>> state_saved for pci_pm_resume_noirq(), so that it always restores the
>> device state from the originally saved data, and avoid calling
>> pci_prepare_to_sleep() for the device.
>>
>> Fixes: 33e4f80ee69b ("ACPI / PM: Ignore spurious SCI wakeups from  
>> suspend-to-idle")
>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

I just found out this patch has a chance to freeze or reboot the system  
during suspend cycles.
What information do you need to debug?

Kai-Heng

>> ---
>>  drivers/pci/pci-driver.c |   17 ++++++++++++++++-
>>  include/linux/pci.h      |    1 +
>>  2 files changed, 17 insertions(+), 1 deletion(-)
>>
>> Index: linux-pm/drivers/pci/pci-driver.c
>> ===================================================================
>> --- linux-pm.orig/drivers/pci/pci-driver.c
>> +++ linux-pm/drivers/pci/pci-driver.c
>> @@ -734,6 +734,8 @@ static int pci_pm_suspend(struct device
>>  	struct pci_dev *pci_dev = to_pci_dev(dev);
>>  	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
>>
>> +	pci_dev->skip_bus_pm = false;
>> +
>>  	if (pci_has_legacy_pm_support(pci_dev))
>>  		return pci_legacy_suspend(dev, PMSG_SUSPEND);
>>
>> @@ -827,7 +829,20 @@ static int pci_pm_suspend_noirq(struct d
>>  		}
>>  	}
>>
>> -	if (!pci_dev->state_saved) {
>> +	if (pci_dev->skip_bus_pm) {
>> +		/*
>> +		 * The function is running for the second time in a row without
>> +		 * going through full resume, which is possible only during
>> +		 * suspend-to-idle in a spurious wakeup case.  Moreover, the
>> +		 * device was originally left in D0, so its power state should
>> +		 * not be changed here and the device register values saved
>> +		 * originally should be restored on resume again.
>> +		 */
>> +		pci_dev->state_saved = true;
>> +	} else if (pci_dev->state_saved) {
>> +		if (pci_dev->current_state == PCI_D0)
>> +			pci_dev->skip_bus_pm = true;
>> +	} else {
>>  		pci_save_state(pci_dev);
>>  		if (pci_power_manageable(pci_dev))
>>  			pci_prepare_to_sleep(pci_dev);
>> Index: linux-pm/include/linux/pci.h
>> ===================================================================
>> --- linux-pm.orig/include/linux/pci.h
>> +++ linux-pm/include/linux/pci.h
>> @@ -344,6 +344,7 @@ struct pci_dev {
>>  						   D3cold, not set for devices
>>  						   powered on/off by the
>>  						   corresponding bridge */
>> +	unsigned int	skip_bus_pm:1;	/* Internal: Skip bus-level PM */
>>  	unsigned int	ignore_hotplug:1;	/* Ignore hotplug events */
>>  	unsigned int	hotplug_user_indicators:1; /* SlotCtl indicators
>>  						      controlled exclusively by
>
> Bjorn, I've assumed no concerns or objections from you regarding this one  
> and
> queued it up.
>
> If that assumption is incorrect, please let me know.