On 09/17/2015 06:59 PM, Rafael J. Wysocki wrote:
> Hi,
>
> On Thu, Sep 17, 2015 at 5:48 PM, Grygorii Strashko
> <grygorii.stras...@ti.com> wrote:
>> Hi,
>>
>> On 09/17/2015 03:07 AM, Rafael J. Wysocki wrote:
>>> On Wednesday, September 16, 2015 03:27:55 PM Alan Stern wrote:
>>>> On Wed, 16 Sep 2015, Grygorii Strashko wrote:
>>>>
>>>>> I think, It should prohibited to probe devices during suspend/hibernation.
>>>>> And solution introduced in this patch might help to fix it -
>>>>> in general, we could do :
>>>>> - add sync point on suspend enter: wait_for_device_probe() and
>>>>> - prohibit probing: move all devices which will request probing into
>>>>> deferred_probe list
>>>>> - one suspend exit: allow probing and do driver_deferred_probe_trigger
>>>>
>>>> That could work; it's a good idea.
>>>>
>>>>> I'd like to mention here that this patch will work only
>>>>> if dmp_list will be filled according device creation order
>>>>> ("parent<-child" dependencies)
>>>>> *AND* according device's probing order ("supplier<-consumer").
>>>>> So, if there is the case when Parent device can be probed AFTER its
>>>>> children
>>>>> - it will not work, because "parent<-child" dependencies will not be
>>>>> tracked
>>>>> any more :( Sry, I could not even imagine that such crazy case exist :'(
>>>>
>>>> If we avoid moving devices to the end of the dpm_list when they already
>>>> have children, then we should be okay, right?
>>>>
>>>>> Are there any other subsystems with the same behavior like PCI?
>>>>
>>>> I don't know.
>>>>
>>>>> If not - probably, it could be fixed in PCI subsystem using
>>>>> device_pm_move_after() or
>>>>> device_move() in PCIe ports probe.
>>>>> if yes - ... maybe we can scan/re-check and reorder dpm_list on suspend
>>>>> enter and
>>>>> restore ("parent<-child" dependencies).
>>>>
>>>>> Truth is that smth. need to be done 100%. Personally, I was hit by this
>>>>> issue also,
>>>>> and it cost me 3 hours of debugging and I came up with the same patch
>>>>> as
>>>>> Bill Huang, then spent some time trying to understand what is wrong with
>>>>> PCI
>>>>> - finally, I've just changed the order of my devices in DT :)
>>>>>
>>>>> Also, I think, it will be good to have this patch in -next to collect
>>>>> more feedbacks.
>>>>
>>>> I like the idea of forcing all probes during a sleep transition to be
>>>> deferred. We could carry them out just before unfreezing the user
>>>> threads. That combined with the change mentioned above ought to be
>>>> worth testing.
>>>
>>> Agreed.
>>>
>>
>> I've prepared code change which should prohibit devices probing during
>> suspend/hibernation
>> (below). It also expected to fix wait_for_device_probe() to take into
>> account the case
>> when the deferred probe workqueue could be still active.
>>
>> NOTE: It's only compile time tested!
>>
>> I'm very sorry that I'm replying here instead of sending a proper patch -
>> I'm on business trip right now and I will be traveling next week also and
>> will not
>> be able to work on it intensively.
>>
>> If proposed approach is correct I can send RFC/RFT patch/es (or anyone else
>> could
>> pick up it if interested to move forward faster).
>>
>> --
>> regards,
>> -grygorii
>>
>> From d29e554bf1d593c6c52d2902872ba8a6c48a80a8 Mon Sep 17 00:00:00 2001
>> From: Grygorii Strashko <grygorii.stras...@ti.com>
>> Date: Thu, 17 Sep 2015 18:33:54 +0300
>> Subject: [RFC/RFT PATCH] PM / sleep: prohibit devices probing during
>> suspend/hibernation
>>
>> Signed-off-by: Grygorii Strashko <grygorii.stras...@ti.com>
>> ---
>> drivers/base/dd.c | 28 +++++++++++++++++++++++++++-
>> include/linux/device.h | 1 +
>> kernel/power/process.c | 8 ++++++++
>> 3 files changed, 36 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
>> index be0eb46..dcadf30 100644
>> --- a/drivers/base/dd.c
>> +++ b/drivers/base/dd.c
>> @@ -55,6 +55,14 @@ static struct workqueue_struct *deferred_wq;
>> static atomic_t deferred_trigger_count = ATOMIC_INIT(0);
>>
>> /*
>> + * In some cases, like suspend to RAM or hibernation, It might be reasonable
>> + * to prohibit probing of devices as it could be unsafe.
>> + * Once driver_force_probe_deferral is true all drivers probes will
>> + * be forcibly deferred
>> + */
>> +static bool driver_force_probe_deferral;
>
> What about defer_all_probes ?
ok
>
>> +
>> +/*
>> * deferred_probe_work_func() - Retry probing devices in the active list.
>> */
>> static void deferred_probe_work_func(struct work_struct *work)
>> @@ -171,6 +179,14 @@ static void driver_deferred_probe_trigger(void)
>> queue_work(deferred_wq, &deferred_probe_work);
>> }
>>
>> +void device_force_probe_deferral(bool enable)
>
> device_defer_all_probes ?
>
ok
>> +{
>> + driver_force_probe_deferral = enable;
>> + if (!enable)
>> + driver_deferred_probe_trigger();
>> +}
>> +EXPORT_SYMBOL_GPL(device_force_probe_deferral);
>
> That doesn't need to be exported, it is only called by statically linked code.
>
ok
>> +
>> /**
>> * deferred_probe_initcall() - Enable probing of deferred devices
>> *
>> @@ -277,9 +293,15 @@ static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue);
>>
>> static int really_probe(struct device *dev, struct device_driver *drv)
>> {
>> - int ret = 0;
>> + int ret = -EPROBE_DEFER;
>> int local_trigger_count = atomic_read(&deferred_trigger_count);
>>
>> + if (driver_force_probe_deferral) {
>
> What if the above is evaluated before the suspend sequence starts ->
>
>> + dev_dbg(dev, "Driver %s force probe deferral\n", drv->name);
>> + driver_deferred_probe_add(dev);
>> + return ret;
>> + }
>> +
>
> -> and the code below runs after it has started?
>
> Isn't that racy?
No. as below :)
>
>> atomic_inc(&probe_count);
>> pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
>> drv->bus->name, __func__, drv->name, dev_name(dev));
>> @@ -391,6 +413,10 @@ int driver_probe_done(void)
>> */
>> void wait_for_device_probe(void)
>> {
>> + /* wait for the deferred probe workqueue to finish */
>> + if (driver_deferred_probe_enable)
>> + flush_workqueue(deferred_wq);
>> +
>> /* wait for the known devices to complete their probing */
>> wait_event(probe_waitqueue, atomic_read(&probe_count) == 0);
>> async_synchronize_full();
>> diff --git a/include/linux/device.h b/include/linux/device.h
>> index 5d7bc63..c68b8e1 100644
>> --- a/include/linux/device.h
>> +++ b/include/linux/device.h
>> @@ -1034,6 +1034,7 @@ extern int __must_check device_attach(struct device
>> *dev);
>> extern int __must_check driver_attach(struct device_driver *drv);
>> extern void device_initial_probe(struct device *dev);
>> extern int __must_check device_reprobe(struct device *dev);
>> +extern void device_force_probe_deferral(bool enable);
>>
>> /*
>> * Easy functions for dynamically creating devices on the fly
>> diff --git a/kernel/power/process.c b/kernel/power/process.c
>> index 564f786..c13e78d 100644
>> --- a/kernel/power/process.c
>> +++ b/kernel/power/process.c
>> @@ -148,6 +148,13 @@ int freeze_processes(void)
>> if (!error && !oom_killer_disable())
>> error = -EBUSY;
>>
>> + if (!error) {
>> + /** wait for the known devices to complete their probing */
>> + wait_for_device_probe();
>> + device_force_probe_deferral(true);
>> + wait_for_device_probe();
>
> Ah, OK. So the second wait_for_device_probe() avoids the race.
>
> What is the first one for?
That's required to satisfy hibernation restore needs - we should give a chance
to already active probes to finish, because this could be a boot time.
>
> In any case, maybe call that from dpm_suspend_start() after
> dpm_prepare() has run successfully? This is the point we need to
> start to block probing after all.
>
That's what i've thought at the beginning. But, unfortunately, I've
found at least one case when dpm_prepare() is used alone:
hibernation_snapshot() -> dpm_prepare()
As result, I've placed probe sync code in freeze_processes() as it's
called always and for all Low-Power states.
>> + }
>> +
>> if (error)
>> thaw_processes();
>> return error;
>> @@ -190,6 +197,7 @@ void thaw_processes(void)
>> atomic_dec(&system_freezing_cnt);
>> pm_freezing = false;
>> pm_nosig_freezing = false;
>> + device_force_probe_deferral(false);
>
> And why don't you call that from dpm_resume_end()?
Same is here.
hibernate.c (2 matches)
hibernation_snapshot, line 367: dpm_complete(PMSG_RECOVER);
hibernation_snapshot, line 398: dpm_complete(msg);
I'm very sorry for delayed reply.
--
regards,
-grygorii
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
