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 ?
> +
> +/*
> * 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 ?
> +{
> + 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.
> +
> /**
> * 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?
> 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?
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.
> + }
> +
> 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()?
>
> oom_killer_enable();
>
> --
Thanks,
Rafael
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