Re: [PATCH net-next 1/4] ethtool: runtime-resume netdev parent before ethtool ioctl ops

Re: [PATCH net-next 1/4] ethtool: runtime-resume netdev parent before ethtool ioctl ops

[Grygorii Strashko]

On 01/08/2021 13:36, Heiner Kallweit wrote:
> If a network device is runtime-suspended then:
> - network device may be flagged as detached and all ethtool ops (even if not
>    accessing the device) will fail because netif_device_present() returns
>    false
> - ethtool ops may fail because device is not accessible (e.g. because being
>    in D3 in case of a PCI device)
> 
> It may not be desirable that userspace can't use even simple ethtool ops
> that not access the device if interface or link is down. To be more friendly
> to userspace let's ensure that device is runtime-resumed when executing the
> respective ethtool op in kernel.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> ---
>   net/ethtool/ioctl.c | 18 +++++++++++++++---
>   1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
> index baa5d1004..b7ff9abe7 100644
> --- a/net/ethtool/ioctl.c
> +++ b/net/ethtool/ioctl.c
> @@ -23,6 +23,7 @@
>   #include <linux/rtnetlink.h>
>   #include <linux/sched/signal.h>
>   #include <linux/net.h>
> +#include <linux/pm_runtime.h>
>   #include <net/devlink.h>
>   #include <net/xdp_sock_drv.h>
>   #include <net/flow_offload.h>
> @@ -2589,7 +2590,7 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>   	int rc;
>   	netdev_features_t old_features;
>   
> -	if (!dev || !netif_device_present(dev))
> +	if (!dev)
>   		return -ENODEV;
>   
>   	if (copy_from_user(&ethcmd, useraddr, sizeof(ethcmd)))
> @@ -2645,10 +2646,18 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>   			return -EPERM;
>   	}
>   
> +	if (dev->dev.parent)
> +		pm_runtime_get_sync(dev->dev.parent);

the PM Runtime should allow to wake up parent when child is resumed if everything is configured properly.

rpm_resume()
...
     if (!parent && dev->parent) {
  --> here

So, hence PM runtime calls are moved to from drivers to net_core wouldn't be more correct approach to
enable PM runtime for netdev->dev and lets PM runtime do the job?

But, to be honest, I'm not sure adding PM runtime manipulation to the net core is a good idea -
at minimum it might be tricky and required very careful approach (especially in err path).
For example, even in this patch you do not check return value of pm_runtime_get_sync() and in
commit bd869245a3dc ("net: core: try to runtime-resume detached device in __dev_open") also actualy.


The TI CPSW driver may also be placed in non reachable state when netdev is closed (and even lose context),
but we do not use netif_device_detach() (so netdev is accessible through netdev_ops/ethtool_ops),
but instead wake up device by runtime PM for allowed operations or just save requested configuration which
is applied at netdev->open() time then.
I feel that using netif_device_detach() in PM runtime sounds like a too heavy approach ;)

huh, see it's merged already, so...

> +
> +	if (!netif_device_present(dev)) {
> +		rc = -ENODEV;
> +		goto out;
> +	}
> +
>   	if (dev->ethtool_ops->begin) {
>   		rc = dev->ethtool_ops->begin(dev);
> -		if (rc  < 0)
> -			return rc;
> +		if (rc < 0)
> +			goto out;
>   	}
>   	old_features = dev->features;
>   
> @@ -2867,6 +2876,9 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>   
>   	if (old_features != dev->features)
>   		netdev_features_change(dev);
> +out:
> +	if (dev->dev.parent)
> +		pm_runtime_put(dev->dev.parent);
>   
>   	return rc;
>   }
> 

-- 
Best regards,
grygorii

Re: [PATCH net-next 1/4] ethtool: runtime-resume netdev parent before ethtool ioctl ops

[Heiner Kallweit]

On 03.08.2021 22:41, Grygorii Strashko wrote:
> 
> 
> On 01/08/2021 13:36, Heiner Kallweit wrote:
>> If a network device is runtime-suspended then:
>> - network device may be flagged as detached and all ethtool ops (even if not
>>    accessing the device) will fail because netif_device_present() returns
>>    false
>> - ethtool ops may fail because device is not accessible (e.g. because being
>>    in D3 in case of a PCI device)
>>
>> It may not be desirable that userspace can't use even simple ethtool ops
>> that not access the device if interface or link is down. To be more friendly
>> to userspace let's ensure that device is runtime-resumed when executing the
>> respective ethtool op in kernel.
>>
>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>> ---
>>   net/ethtool/ioctl.c | 18 +++++++++++++++---
>>   1 file changed, 15 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
>> index baa5d1004..b7ff9abe7 100644
>> --- a/net/ethtool/ioctl.c
>> +++ b/net/ethtool/ioctl.c
>> @@ -23,6 +23,7 @@
>>   #include <linux/rtnetlink.h>
>>   #include <linux/sched/signal.h>
>>   #include <linux/net.h>
>> +#include <linux/pm_runtime.h>
>>   #include <net/devlink.h>
>>   #include <net/xdp_sock_drv.h>
>>   #include <net/flow_offload.h>
>> @@ -2589,7 +2590,7 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>       int rc;
>>       netdev_features_t old_features;
>>   -    if (!dev || !netif_device_present(dev))
>> +    if (!dev)
>>           return -ENODEV;
>>         if (copy_from_user(&ethcmd, useraddr, sizeof(ethcmd)))
>> @@ -2645,10 +2646,18 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>               return -EPERM;
>>       }
>>   +    if (dev->dev.parent)
>> +        pm_runtime_get_sync(dev->dev.parent);
> 
> the PM Runtime should allow to wake up parent when child is resumed if everything is configured properly.
> 
Not sure if there's any case yet where the netdev-embedded device is power-managed.
Typically only the parent (e.g. a PCI device) is.

> rpm_resume()
> ...
>     if (!parent && dev->parent) {
>  --> here
> 
Currently we don't get that far because we will bail out here already:

else if (dev->power.disable_depth > 0)
		retval = -EACCES;

If netdev-embedded device isn't power-managed then disable_depth is 1.

> So, hence PM runtime calls are moved to from drivers to net_core wouldn't be more correct approach to
> enable PM runtime for netdev->dev and lets PM runtime do the job?
> 
Where would netdev->dev be runtime-resumed so that netif_device_present() passes?
Wouldn't we then need RPM ops for the parent (e.g. PCI) and for netdev->dev?
E.g. the parent runtime-resume can be triggered by a PCI PME, then it would
have to resume netdev->dev.

> But, to be honest, I'm not sure adding PM runtime manipulation to the net core is a good idea -

The TI CPSW driver runtime-resumes the device in begin ethtool op and suspends
it in complete. This pattern is used in more than one driver and may be worth
being moved to the core.

> at minimum it might be tricky and required very careful approach (especially in err path).
> For example, even in this patch you do not check return value of pm_runtime_get_sync() and in
> commit bd869245a3dc ("net: core: try to runtime-resume detached device in __dev_open") also actualy.

The pm_runtime_get_sync() calls are attempts here. We don't want to bail out if a device
doesn't support RPM. I agree that checking the return code could make sense, but then we would
have to be careful which error codes we consider as failed.

> 
> 
> The TI CPSW driver may also be placed in non reachable state when netdev is closed (and even lose context),
> but we do not use netif_device_detach() (so netdev is accessible through netdev_ops/ethtool_ops),
> but instead wake up device by runtime PM for allowed operations or just save requested configuration which
> is applied at netdev->open() time then.
> I feel that using netif_device_detach() in PM runtime sounds like a too heavy approach ;)
> 
That's not a rare pattern when suspending or runtime-suspending to prevent different types
of access to a not accessible device. But yes, it's relatively big hammer ..

> huh, see it's merged already, so...
> 
>> +
>> +    if (!netif_device_present(dev)) {
>> +        rc = -ENODEV;
>> +        goto out;
>> +    }
>> +
>>       if (dev->ethtool_ops->begin) {
>>           rc = dev->ethtool_ops->begin(dev);
>> -        if (rc  < 0)
>> -            return rc;
>> +        if (rc < 0)
>> +            goto out;
>>       }
>>       old_features = dev->features;
>>   @@ -2867,6 +2876,9 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>         if (old_features != dev->features)
>>           netdev_features_change(dev);
>> +out:
>> +    if (dev->dev.parent)
>> +        pm_runtime_put(dev->dev.parent);
>>         return rc;
>>   }
>>
> 

Re: [PATCH net-next 1/4] ethtool: runtime-resume netdev parent before ethtool ioctl ops

[Grygorii Strashko]

On 04/08/2021 00:32, Heiner Kallweit wrote:
> On 03.08.2021 22:41, Grygorii Strashko wrote:
>>
>>
>> On 01/08/2021 13:36, Heiner Kallweit wrote:
>>> If a network device is runtime-suspended then:
>>> - network device may be flagged as detached and all ethtool ops (even if not
>>>     accessing the device) will fail because netif_device_present() returns
>>>     false
>>> - ethtool ops may fail because device is not accessible (e.g. because being
>>>     in D3 in case of a PCI device)
>>>
>>> It may not be desirable that userspace can't use even simple ethtool ops
>>> that not access the device if interface or link is down. To be more friendly
>>> to userspace let's ensure that device is runtime-resumed when executing the
>>> respective ethtool op in kernel.
>>>
>>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>>> ---
>>>    net/ethtool/ioctl.c | 18 +++++++++++++++---
>>>    1 file changed, 15 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
>>> index baa5d1004..b7ff9abe7 100644
>>> --- a/net/ethtool/ioctl.c
>>> +++ b/net/ethtool/ioctl.c
>>> @@ -23,6 +23,7 @@
>>>    #include <linux/rtnetlink.h>
>>>    #include <linux/sched/signal.h>
>>>    #include <linux/net.h>
>>> +#include <linux/pm_runtime.h>
>>>    #include <net/devlink.h>
>>>    #include <net/xdp_sock_drv.h>
>>>    #include <net/flow_offload.h>
>>> @@ -2589,7 +2590,7 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>>        int rc;
>>>        netdev_features_t old_features;
>>>    -    if (!dev || !netif_device_present(dev))
>>> +    if (!dev)
>>>            return -ENODEV;
>>>          if (copy_from_user(&ethcmd, useraddr, sizeof(ethcmd)))
>>> @@ -2645,10 +2646,18 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>>                return -EPERM;
>>>        }
>>>    +    if (dev->dev.parent)
>>> +        pm_runtime_get_sync(dev->dev.parent);
>>
>> the PM Runtime should allow to wake up parent when child is resumed if everything is configured properly.
>>
> Not sure if there's any case yet where the netdev-embedded device is power-managed.
> Typically only the parent (e.g. a PCI device) is.
> 
>> rpm_resume()
>> ...
>>      if (!parent && dev->parent) {
>>   --> here
>>
> Currently we don't get that far because we will bail out here already:
> 
> else if (dev->power.disable_depth > 0)
> 		retval = -EACCES;
> 
> If netdev-embedded device isn't power-managed then disable_depth is 1.

Right. But if pm_runtime_enable() is added for ndev->dev then PM runtime will start working for it
and should handle parent properly - from my experience, every time any code need manipulate with "parent" or
smth. else to make PM runtime working it means smth. is wrong.

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index f6197774048b..33b72b788aa2 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1963,6 +1963,7 @@ int netdev_register_kobject(struct net_device *ndev)
         }
  
         pm_runtime_set_memalloc_noio(dev, true);
+       pm_runtime_enable(dev);
  
         return error;
  }


> 
>> So, hence PM runtime calls are moved to from drivers to net_core wouldn't be more correct approach to
>> enable PM runtime for netdev->dev and lets PM runtime do the job?
>>
> Where would netdev->dev be runtime-resumed so that netif_device_present() passes?

That's the biggest issues here. Some driver uses netif_device_detach() in PM runtime and, this way, introduces custom dependency
between Core device PM (runtime) sate and Net core, other driver does not do.
Does it means every driver with PM runtime now have to be updated to indicate it PM state to Net core with netif_device_detach()?
Why? Why return value from pm_runtime_get calls is not enough?

Believe me it's terrible idea to introduce custom PM state dependency between PM runtime and Net core,
for example it took years to sync properly System wide suspend and PM runtime which are separate framworks.

By the way netif_device_detach() during System Wide suspend is looks perfectly valid, because entering
System wide Suspend should prohibit any access to netdev at some stage. And that's what 99% of network drivers are doing
(actually I can find only ./realtek/r8169_main.c which abuse netif_device_detach() function and,
I assume, it is your case)

> Wouldn't we then need RPM ops for the parent (e.g. PCI) and for netdev->dev?

No. as I know -  netdev->dev can be declared as pm_runtime_no_callbacks(&adap->dev);
I2C adapter might be a good example to check.

> E.g. the parent runtime-resume can be triggered by a PCI PME, then it would
> have to resume netdev->dev.
> 
>> But, to be honest, I'm not sure adding PM runtime manipulation to the net core is a good idea -
> 
> The TI CPSW driver runtime-resumes the device in begin ethtool op and suspends
> it in complete. This pattern is used in more than one driver and may be worth
> being moved to the core.

I'm not against code refactoring and optimization, but in my opinion it has to be done right from the beginning or
not done at all.

> 
>> at minimum it might be tricky and required very careful approach (especially in err path).
>> For example, even in this patch you do not check return value of pm_runtime_get_sync() and in
>> commit bd869245a3dc ("net: core: try to runtime-resume detached device in __dev_open") also actualy.
> 
> The pm_runtime_get_sync() calls are attempts here. We don't want to bail out if a device
> doesn't support RPM.

And if 'parent' is not supporting PM runtime - it, as i see, should be handled by PM runtime core properly.

I agree that checking the return code could make sense, but then we would
> have to be careful which error codes we consider as failed.

huh. you can't 'try' pm_runtime_get_sync() and then align on netif_device_present() :(

might be, some how, it will work for r8169_main, but will not work for others.
- no checking pm_runtime_get_sync() err code will cause PM runtime 'usage_count' leak
- no checking pm_runtime_get_sync() err may cause to continue( for TI CPSW for example) with
   device in undefined PM state ("disabled" or "half-enabled") and so crash later.



> 
>>
>>
>> The TI CPSW driver may also be placed in non reachable state when netdev is closed (and even lose context),
>> but we do not use netif_device_detach() (so netdev is accessible through netdev_ops/ethtool_ops),
>> but instead wake up device by runtime PM for allowed operations or just save requested configuration which
>> is applied at netdev->open() time then.
>> I feel that using netif_device_detach() in PM runtime sounds like a too heavy approach ;)
>>
> That's not a rare pattern when suspending or runtime-suspending to prevent different types
> of access to a not accessible device. But yes, it's relatively big hammer ..

Again, netif_device_detach() seems correct for System wide suspend, but in my opinion - it's
not correct for PM runtime.

Sry, with all do respect, first corresponding driver has to be fixed and not Net core hacked to support it.

Further decisions is up to maintainers.


> 
>> huh, see it's merged already, so...
>>
>>> +
>>> +    if (!netif_device_present(dev)) {
>>> +        rc = -ENODEV;
>>> +        goto out;
>>> +    }
>>> +
>>>        if (dev->ethtool_ops->begin) {
>>>            rc = dev->ethtool_ops->begin(dev);
>>> -        if (rc  < 0)
>>> -            return rc;
>>> +        if (rc < 0)
>>> +            goto out;
>>>        }
>>>        old_features = dev->features;
>>>    @@ -2867,6 +2876,9 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>>          if (old_features != dev->features)
>>>            netdev_features_change(dev);
>>> +out:
>>> +    if (dev->dev.parent)
>>> +        pm_runtime_put(dev->dev.parent);
>>>          return rc;
>>>    }
>>>
>>
> 

-- 
Best regards,
grygorii

Re: [PATCH net-next 1/4] ethtool: runtime-resume netdev parent before ethtool ioctl ops

[Heiner Kallweit]

On 04.08.2021 10:43, Grygorii Strashko wrote:
> 
> 
> On 04/08/2021 00:32, Heiner Kallweit wrote:
>> On 03.08.2021 22:41, Grygorii Strashko wrote:
>>>
>>>
>>> On 01/08/2021 13:36, Heiner Kallweit wrote:
>>>> If a network device is runtime-suspended then:
>>>> - network device may be flagged as detached and all ethtool ops (even if not
>>>>     accessing the device) will fail because netif_device_present() returns
>>>>     false
>>>> - ethtool ops may fail because device is not accessible (e.g. because being
>>>>     in D3 in case of a PCI device)
>>>>
>>>> It may not be desirable that userspace can't use even simple ethtool ops
>>>> that not access the device if interface or link is down. To be more friendly
>>>> to userspace let's ensure that device is runtime-resumed when executing the
>>>> respective ethtool op in kernel.
>>>>
>>>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>>>> ---
>>>>    net/ethtool/ioctl.c | 18 +++++++++++++++---
>>>>    1 file changed, 15 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
>>>> index baa5d1004..b7ff9abe7 100644
>>>> --- a/net/ethtool/ioctl.c
>>>> +++ b/net/ethtool/ioctl.c
>>>> @@ -23,6 +23,7 @@
>>>>    #include <linux/rtnetlink.h>
>>>>    #include <linux/sched/signal.h>
>>>>    #include <linux/net.h>
>>>> +#include <linux/pm_runtime.h>
>>>>    #include <net/devlink.h>
>>>>    #include <net/xdp_sock_drv.h>
>>>>    #include <net/flow_offload.h>
>>>> @@ -2589,7 +2590,7 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>>>        int rc;
>>>>        netdev_features_t old_features;
>>>>    -    if (!dev || !netif_device_present(dev))
>>>> +    if (!dev)
>>>>            return -ENODEV;
>>>>          if (copy_from_user(&ethcmd, useraddr, sizeof(ethcmd)))
>>>> @@ -2645,10 +2646,18 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>>>                return -EPERM;
>>>>        }
>>>>    +    if (dev->dev.parent)
>>>> +        pm_runtime_get_sync(dev->dev.parent);
>>>
>>> the PM Runtime should allow to wake up parent when child is resumed if everything is configured properly.
>>>
>> Not sure if there's any case yet where the netdev-embedded device is power-managed.
>> Typically only the parent (e.g. a PCI device) is.
>>
>>> rpm_resume()
>>> ...
>>>      if (!parent && dev->parent) {
>>>   --> here
>>>
>> Currently we don't get that far because we will bail out here already:
>>
>> else if (dev->power.disable_depth > 0)
>>         retval = -EACCES;
>>
>> If netdev-embedded device isn't power-managed then disable_depth is 1.
> 
> Right. But if pm_runtime_enable() is added for ndev->dev then PM runtime will start working for it
> and should handle parent properly - from my experience, every time any code need manipulate with "parent" or
> smth. else to make PM runtime working it means smth. is wrong.
> 
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index f6197774048b..33b72b788aa2 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -1963,6 +1963,7 @@ int netdev_register_kobject(struct net_device *ndev)
>         }
>  
>         pm_runtime_set_memalloc_noio(dev, true);
> +       pm_runtime_enable(dev);
>  
>         return error;
>  }
> 
> 
>>
>>> So, hence PM runtime calls are moved to from drivers to net_core wouldn't be more correct approach to
>>> enable PM runtime for netdev->dev and lets PM runtime do the job?
>>>
>> Where would netdev->dev be runtime-resumed so that netif_device_present() passes?
> 
> That's the biggest issues here. Some driver uses netif_device_detach() in PM runtime and, this way, introduces custom dependency
> between Core device PM (runtime) sate and Net core, other driver does not do.
> Does it means every driver with PM runtime now have to be updated to indicate it PM state to Net core with netif_device_detach()?

No, that's not needed.

> Why? Why return value from pm_runtime_get calls is not enough?
> 
> Believe me it's terrible idea to introduce custom PM state dependency between PM runtime and Net core,
> for example it took years to sync properly System wide suspend and PM runtime which are separate framworks.
> 
> By the way netif_device_detach() during System Wide suspend is looks perfectly valid, because entering
> System wide Suspend should prohibit any access to netdev at some stage. And that's what 99% of network drivers are doing
> (actually I can find only ./realtek/r8169_main.c which abuse netif_device_detach() function and,
> I assume, it is your case)
> 
Actually I was inspired by the Intel drivers, see e.g. __igc_shutdown(). They also detach the
netdevice on runtime suspend. One reason is that several core functions check for device
presence before e.g. calling a ndo callback. Example: dev_set_mtu_ext()
Same applies for __dev_set_rx_mode(). Therefore I wondered whether cpsw_ndo_set_rx_mode()
- that does not include runtime-resuming the device - may be called when device is
runtime-suspended, e.g. if interface is up, but link is down.

>> Wouldn't we then need RPM ops for the parent (e.g. PCI) and for netdev->dev?
> 
> No. as I know -  netdev->dev can be declared as pm_runtime_no_callbacks(&adap->dev);
> I2C adapter might be a good example to check.
> 
>> E.g. the parent runtime-resume can be triggered by a PCI PME, then it would
>> have to resume netdev->dev.
>>
>>> But, to be honest, I'm not sure adding PM runtime manipulation to the net core is a good idea -
>>
>> The TI CPSW driver runtime-resumes the device in begin ethtool op and suspends
>> it in complete. This pattern is used in more than one driver and may be worth
>> being moved to the core.
> 
> I'm not against code refactoring and optimization, but in my opinion it has to be done right from the beginning or
> not done at all.
> 
>>
>>> at minimum it might be tricky and required very careful approach (especially in err path).
>>> For example, even in this patch you do not check return value of pm_runtime_get_sync() and in
>>> commit bd869245a3dc ("net: core: try to runtime-resume detached device in __dev_open") also actualy.
>>
>> The pm_runtime_get_sync() calls are attempts here. We don't want to bail out if a device
>> doesn't support RPM.
> 
> And if 'parent' is not supporting PM runtime - it, as i see, should be handled by PM runtime core properly.
> 
> I agree that checking the return code could make sense, but then we would
>> have to be careful which error codes we consider as failed.
> 
> huh. you can't 'try' pm_runtime_get_sync() and then align on netif_device_present() :(
> 
> might be, some how, it will work for r8169_main, but will not work for others.
> - no checking pm_runtime_get_sync() err code will cause PM runtime 'usage_count' leak

No. pm_runtime_get_sync() always bumps the usage count, no matter whether it fails or not.
This makes it easy to deal with this. The problem you describe exists with
pm_runtime_resume_and_get(). That's why I wondered whether we should annotate this
function as __must_check. See here:
https://lore.kernel.org/linux-pm/CAJZ5v0gps0C2923VqM8876npvhcETsyN+ajAkBKX5kf49J0+Mg@mail.gmail.com/T/#t

> - no checking pm_runtime_get_sync() err may cause to continue( for TI CPSW for example) with
>   device in undefined PM state ("disabled" or "half-enabled") and so crash later.
> 
I'd say 95% of rpm callers don't check the return value. I'm not saying this is a good thing,
but obviously it doesn't cause relevant harm.

> 
> 
>>
>>>
>>>
>>> The TI CPSW driver may also be placed in non reachable state when netdev is closed (and even lose context),
>>> but we do not use netif_device_detach() (so netdev is accessible through netdev_ops/ethtool_ops),
>>> but instead wake up device by runtime PM for allowed operations or just save requested configuration which
>>> is applied at netdev->open() time then.
>>> I feel that using netif_device_detach() in PM runtime sounds like a too heavy approach ;)
>>>
>> That's not a rare pattern when suspending or runtime-suspending to prevent different types
>> of access to a not accessible device. But yes, it's relatively big hammer ..
> 
> Again, netif_device_detach() seems correct for System wide suspend, but in my opinion - it's
> not correct for PM runtime.
> 
> Sry, with all do respect, first corresponding driver has to be fixed and not Net core hacked to support it.
> 
> Further decisions is up to maintainers.
> 
> 
>>
>>> huh, see it's merged already, so...
>>>
>>>> +
>>>> +    if (!netif_device_present(dev)) {
>>>> +        rc = -ENODEV;
>>>> +        goto out;
>>>> +    }
>>>> +
>>>>        if (dev->ethtool_ops->begin) {
>>>>            rc = dev->ethtool_ops->begin(dev);
>>>> -        if (rc  < 0)
>>>> -            return rc;
>>>> +        if (rc < 0)
>>>> +            goto out;
>>>>        }
>>>>        old_features = dev->features;
>>>>    @@ -2867,6 +2876,9 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>>>          if (old_features != dev->features)
>>>>            netdev_features_change(dev);
>>>> +out:
>>>> +    if (dev->dev.parent)
>>>> +        pm_runtime_put(dev->dev.parent);
>>>>          return rc;
>>>>    }
>>>>
>>>
>>
> 

Re: [PATCH net-next 1/4] ethtool: runtime-resume netdev parent before ethtool ioctl ops

[Grygorii Strashko]

On 04/08/2021 22:33, Heiner Kallweit wrote:
> On 04.08.2021 10:43, Grygorii Strashko wrote:
>>
>>
>> On 04/08/2021 00:32, Heiner Kallweit wrote:
>>> On 03.08.2021 22:41, Grygorii Strashko wrote:
>>>>
>>>>
>>>> On 01/08/2021 13:36, Heiner Kallweit wrote:
>>>>> If a network device is runtime-suspended then:
>>>>> - network device may be flagged as detached and all ethtool ops (even if not
>>>>>      accessing the device) will fail because netif_device_present() returns
>>>>>      false
>>>>> - ethtool ops may fail because device is not accessible (e.g. because being
>>>>>      in D3 in case of a PCI device)
>>>>>
>>>>> It may not be desirable that userspace can't use even simple ethtool ops
>>>>> that not access the device if interface or link is down. To be more friendly
>>>>> to userspace let's ensure that device is runtime-resumed when executing the
>>>>> respective ethtool op in kernel.
>>>>>
>>>>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>>>>> ---
>>>>>     net/ethtool/ioctl.c | 18 +++++++++++++++---
>>>>>     1 file changed, 15 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
>>>>> index baa5d1004..b7ff9abe7 100644
>>>>> --- a/net/ethtool/ioctl.c
>>>>> +++ b/net/ethtool/ioctl.c
>>>>> @@ -23,6 +23,7 @@
>>>>>     #include <linux/rtnetlink.h>
>>>>>     #include <linux/sched/signal.h>
>>>>>     #include <linux/net.h>
>>>>> +#include <linux/pm_runtime.h>
>>>>>     #include <net/devlink.h>
>>>>>     #include <net/xdp_sock_drv.h>
>>>>>     #include <net/flow_offload.h>
>>>>> @@ -2589,7 +2590,7 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>>>>         int rc;
>>>>>         netdev_features_t old_features;
>>>>>     -    if (!dev || !netif_device_present(dev))
>>>>> +    if (!dev)
>>>>>             return -ENODEV;
>>>>>           if (copy_from_user(&ethcmd, useraddr, sizeof(ethcmd)))
>>>>> @@ -2645,10 +2646,18 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>>>>                 return -EPERM;
>>>>>         }
>>>>>     +    if (dev->dev.parent)
>>>>> +        pm_runtime_get_sync(dev->dev.parent);
>>>>
>>>> the PM Runtime should allow to wake up parent when child is resumed if everything is configured properly.
>>>>
>>> Not sure if there's any case yet where the netdev-embedded device is power-managed.
>>> Typically only the parent (e.g. a PCI device) is.
>>>
>>>> rpm_resume()
>>>> ...
>>>>       if (!parent && dev->parent) {
>>>>    --> here
>>>>
>>> Currently we don't get that far because we will bail out here already:
>>>
>>> else if (dev->power.disable_depth > 0)
>>>          retval = -EACCES;
>>>
>>> If netdev-embedded device isn't power-managed then disable_depth is 1.
>>
>> Right. But if pm_runtime_enable() is added for ndev->dev then PM runtime will start working for it
>> and should handle parent properly - from my experience, every time any code need manipulate with "parent" or
>> smth. else to make PM runtime working it means smth. is wrong.
>>
>> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
>> index f6197774048b..33b72b788aa2 100644
>> --- a/net/core/net-sysfs.c
>> +++ b/net/core/net-sysfs.c
>> @@ -1963,6 +1963,7 @@ int netdev_register_kobject(struct net_device *ndev)
>>          }
>>   
>>          pm_runtime_set_memalloc_noio(dev, true);
>> +       pm_runtime_enable(dev);
>>   
>>          return error;
>>   }
>>
>>
>>>
>>>> So, hence PM runtime calls are moved to from drivers to net_core wouldn't be more correct approach to
>>>> enable PM runtime for netdev->dev and lets PM runtime do the job?
>>>>
>>> Where would netdev->dev be runtime-resumed so that netif_device_present() passes?
>>
>> That's the biggest issues here. Some driver uses netif_device_detach() in PM runtime and, this way, introduces custom dependency
>> between Core device PM (runtime) sate and Net core, other driver does not do.
>> Does it means every driver with PM runtime now have to be updated to indicate it PM state to Net core with netif_device_detach()?
> 
> No, that's not needed.
> 
>> Why? Why return value from pm_runtime_get calls is not enough?
>>
>> Believe me it's terrible idea to introduce custom PM state dependency between PM runtime and Net core,
>> for example it took years to sync properly System wide suspend and PM runtime which are separate framworks.
>>
>> By the way netif_device_detach() during System Wide suspend is looks perfectly valid, because entering
>> System wide Suspend should prohibit any access to netdev at some stage. And that's what 99% of network drivers are doing
>> (actually I can find only ./realtek/r8169_main.c which abuse netif_device_detach() function and,
>> I assume, it is your case)
>>
> Actually I was inspired by the Intel drivers, see e.g. __igc_shutdown(). They also detach the
> netdevice on runtime suspend. One reason is that several core functions check for device
> presence before e.g. calling a ndo callback. Example: dev_set_mtu_ext()

right and also:
- netlink - which you've hacked already
- 8021q: vlan_dev_ioctl/vlan_dev_neigh_setup/vlan_add_rx_filter_info/vlan_kill_rx_filter_info


> Same applies for __dev_set_rx_mode(). Therefore I wondered whether cpsw_ndo_set_rx_mode()
> - that does not include runtime-resuming the device - may be called when device is
> runtime-suspended, e.g. if interface is up, but link is down.

CPSW doesn't manage PM runtime in link status handler, as it has only on/off state and off state can cause full
context loss restore of which is expensive and hard to implement. And for most of netdev drivers no aggressive PM runtime
is implemented exactly because of that (mac/vlan/fdb/mdb/...). Common patterns:

(a)
.probe
  -get
.remove
  -put

(b)
.probe
  -get
  -put
.open
  -get
.close
  -put
.protect places which may be called when netif is down

The CPSW follows (b) and so cpsw_ndo_set_rx_mode() can't be called when when device is
runtime-suspended.

I assume, some hw like PCI, can have more PM states and in some of them keep HW context intact.


> 
>>> Wouldn't we then need RPM ops for the parent (e.g. PCI) and for netdev->dev?
>>
>> No. as I know -  netdev->dev can be declared as pm_runtime_no_callbacks(&adap->dev);
>> I2C adapter might be a good example to check.
>>
>>> E.g. the parent runtime-resume can be triggered by a PCI PME, then it would
>>> have to resume netdev->dev.
>>>
>>>> But, to be honest, I'm not sure adding PM runtime manipulation to the net core is a good idea -
>>>
>>> The TI CPSW driver runtime-resumes the device in begin ethtool op and suspends
>>> it in complete. This pattern is used in more than one driver and may be worth
>>> being moved to the core.
>>
>> I'm not against code refactoring and optimization, but in my opinion it has to be done right from the beginning or
>> not done at all.
>>
>>>
>>>> at minimum it might be tricky and required very careful approach (especially in err path).
>>>> For example, even in this patch you do not check return value of pm_runtime_get_sync() and in
>>>> commit bd869245a3dc ("net: core: try to runtime-resume detached device in __dev_open") also actualy.
>>>
>>> The pm_runtime_get_sync() calls are attempts here. We don't want to bail out if a device
>>> doesn't support RPM.
>>
>> And if 'parent' is not supporting PM runtime - it, as i see, should be handled by PM runtime core properly.
>>
>> I agree that checking the return code could make sense, but then we would
>>> have to be careful which error codes we consider as failed.
>>
>> huh. you can't 'try' pm_runtime_get_sync() and then align on netif_device_present() :(
>>
>> might be, some how, it will work for r8169_main, but will not work for others.
>> - no checking pm_runtime_get_sync() err code will cause PM runtime 'usage_count' leak
> 
> No. pm_runtime_get_sync() always bumps the usage count, no matter whether it fails or not.


> This makes it easy to deal with this. The problem you describe exists with
> pm_runtime_resume_and_get(). That's why I wondered whether we should annotate this
> function as __must_check. See here:
> https://lore.kernel.org/linux-pm/CAJZ5v0gps0C2923VqM8876npvhcETsyN+ajAkBKX5kf49J0+Mg@mail.gmail.com/T/#t
> 
>> - no checking pm_runtime_get_sync() err may cause to continue( for TI CPSW for example) with
>>    device in undefined PM state ("disabled" or "half-enabled") and so crash later.
>>
> I'd say 95% of rpm callers don't check the return value. I'm not saying this is a good thing,
> but obviously it doesn't cause relevant harm.

this is completely wrong assumption as PM errors cause silent stuck, undefined behavior or dumps (sometimes delayed)
which is terribly hard to root cause.

yes. many drivers do not check, but over last few years more and more strict policies applied to avoid that and
in many case no checking return code - is red flag and patch reject.
Don't like that phrase ;), but "It doesn't mean that incorrect code has to be copy-pasted all over the places"

this is correct get pattern for get:
	ret = pm_runtime_get_sync(&pdev->dev);
	if (ret < 0) {
		pm_runtime_put_noidle(&pdev->dev);
		return ret;
	}

My strong opinion
  - PM runtime return code must be checked.
  - get rid of netif_device_detach() in r8169

by the way, have you tried below test with your driver (not sure how it works for you):

.rtl_open
  - pm_runtime_get_sync
  - pm_runtime_put_sync - usage_count == 0
.r8169_phylink_handler
  - pm_request_resume - why async? still usage_count == 0
.some ethtool request to go through dev_ethtool()
  - pm_runtime_get_sync
  - pm_runtime_put - async, usage_count == 0
    ^ would not it put r8169 in runtime-suspended state while link is still UP?
  

> 
>>
>>
>>>
>>>>
>>>>
>>>> The TI CPSW driver may also be placed in non reachable state when netdev is closed (and even lose context),
>>>> but we do not use netif_device_detach() (so netdev is accessible through netdev_ops/ethtool_ops),
>>>> but instead wake up device by runtime PM for allowed operations or just save requested configuration which
>>>> is applied at netdev->open() time then.
>>>> I feel that using netif_device_detach() in PM runtime sounds like a too heavy approach ;)
>>>>
>>> That's not a rare pattern when suspending or runtime-suspending to prevent different types
>>> of access to a not accessible device. But yes, it's relatively big hammer ..
>>
>> Again, netif_device_detach() seems correct for System wide suspend, but in my opinion - it's
>> not correct for PM runtime.
>>
>> Sry, with all do respect, first corresponding driver has to be fixed and not Net core hacked to support it.
>>
>> Further decisions is up to maintainers.
>>
>>
>>>
>>>> huh, see it's merged already, so...
>>>>
>>>>> +
>>>>> +    if (!netif_device_present(dev)) {
>>>>> +        rc = -ENODEV;
>>>>> +        goto out;
>>>>> +    }
>>>>> +
>>>>>         if (dev->ethtool_ops->begin) {
>>>>>             rc = dev->ethtool_ops->begin(dev);
>>>>> -        if (rc  < 0)
>>>>> -            return rc;
>>>>> +        if (rc < 0)
>>>>> +            goto out;
>>>>>         }
>>>>>         old_features = dev->features;
>>>>>     @@ -2867,6 +2876,9 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>>>>           if (old_features != dev->features)
>>>>>             netdev_features_change(dev);
>>>>> +out:
>>>>> +    if (dev->dev.parent)
>>>>> +        pm_runtime_put(dev->dev.parent);
>>>>>           return rc;
>>>>>     }
>>>>>
>>>>
>>>
>>
> 

-- 
Best regards,
grygorii

RE: [PATCH net-next 1/4] ethtool: runtime-resume netdev parent before ethtool ioctl ops

[Joakim Zhang]

> -----Original Message-----
> From: Grygorii Strashko <grygorii.strashko@ti.com>
> Sent: 2021年8月5日 16:21
> To: Heiner Kallweit <hkallweit1@gmail.com>; Jakub Kicinski
> <kuba@kernel.org>; David Miller <davem@davemloft.net>
> Cc: netdev@vger.kernel.org; Linux PM list <linux-pm@vger.kernel.org>;
> Andrew Lunn <andrew@lunn.ch>; Florian Fainelli <f.fainelli@gmail.com>
> Subject: Re: [PATCH net-next 1/4] ethtool: runtime-resume netdev parent
> before ethtool ioctl ops
> 
> 
> 
> On 04/08/2021 22:33, Heiner Kallweit wrote:
> > On 04.08.2021 10:43, Grygorii Strashko wrote:
> >>
> >>
> >> On 04/08/2021 00:32, Heiner Kallweit wrote:
> >>> On 03.08.2021 22:41, Grygorii Strashko wrote:
> >>>>
> >>>>
> >>>> On 01/08/2021 13:36, Heiner Kallweit wrote:
> >>>>> If a network device is runtime-suspended then:
> >>>>> - network device may be flagged as detached and all ethtool ops
> >>>>> (even if not
> >>>>>      accessing the device) will fail because
> >>>>> netif_device_present() returns
> >>>>>      false
> >>>>> - ethtool ops may fail because device is not accessible (e.g.
> >>>>> because being
> >>>>>      in D3 in case of a PCI device)
> >>>>>
> >>>>> It may not be desirable that userspace can't use even simple
> >>>>> ethtool ops that not access the device if interface or link is
> >>>>> down. To be more friendly to userspace let's ensure that device is
> >>>>> runtime-resumed when executing the respective ethtool op in kernel.
> >>>>>
> >>>>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> >>>>> ---
> >>>>>     net/ethtool/ioctl.c | 18 +++++++++++++++---
> >>>>>     1 file changed, 15 insertions(+), 3 deletions(-)
> >>>>>
> >>>>> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c index
> >>>>> baa5d1004..b7ff9abe7 100644
> >>>>> --- a/net/ethtool/ioctl.c
> >>>>> +++ b/net/ethtool/ioctl.c
> >>>>> @@ -23,6 +23,7 @@
> >>>>>     #include <linux/rtnetlink.h>
> >>>>>     #include <linux/sched/signal.h>
> >>>>>     #include <linux/net.h>
> >>>>> +#include <linux/pm_runtime.h>
> >>>>>     #include <net/devlink.h>
> >>>>>     #include <net/xdp_sock_drv.h>
> >>>>>     #include <net/flow_offload.h>
> >>>>> @@ -2589,7 +2590,7 @@ int dev_ethtool(struct net *net, struct
> >>>>> ifreq *ifr)
> >>>>>         int rc;
> >>>>>         netdev_features_t old_features;
> >>>>>     -    if (!dev || !netif_device_present(dev))
> >>>>> +    if (!dev)
> >>>>>             return -ENODEV;
> >>>>>           if (copy_from_user(&ethcmd, useraddr, sizeof(ethcmd)))
> >>>>> @@ -2645,10 +2646,18 @@ int dev_ethtool(struct net *net, struct
> >>>>> ifreq *ifr)
> >>>>>                 return -EPERM;
> >>>>>         }
> >>>>>     +    if (dev->dev.parent)
> >>>>> +        pm_runtime_get_sync(dev->dev.parent);
> >>>>
> >>>> the PM Runtime should allow to wake up parent when child is resumed if
> everything is configured properly.
> >>>>
> >>> Not sure if there's any case yet where the netdev-embedded device is
> power-managed.
> >>> Typically only the parent (e.g. a PCI device) is.
> >>>
> >>>> rpm_resume()
> >>>> ...
> >>>>       if (!parent && dev->parent) {
> >>>>    --> here
> >>>>
> >>> Currently we don't get that far because we will bail out here already:
> >>>
> >>> else if (dev->power.disable_depth > 0)
> >>>          retval = -EACCES;
> >>>
> >>> If netdev-embedded device isn't power-managed then disable_depth is 1.
> >>
> >> Right. But if pm_runtime_enable() is added for ndev->dev then PM
> >> runtime will start working for it and should handle parent properly -
> >> from my experience, every time any code need manipulate with "parent" or
> smth. else to make PM runtime working it means smth. is wrong.
> >>
> >> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c index
> >> f6197774048b..33b72b788aa2 100644
> >> --- a/net/core/net-sysfs.c
> >> +++ b/net/core/net-sysfs.c
> >> @@ -1963,6 +1963,7 @@ int netdev_register_kobject(struct net_device
> >> *ndev)
> >>          }
> >>
> >>          pm_runtime_set_memalloc_noio(dev, true);
> >> +       pm_runtime_enable(dev);
> >>
> >>          return error;
> >>   }
> >>
> >>
> >>>
> >>>> So, hence PM runtime calls are moved to from drivers to net_core
> >>>> wouldn't be more correct approach to enable PM runtime for netdev->dev
> and lets PM runtime do the job?
> >>>>
> >>> Where would netdev->dev be runtime-resumed so that
> netif_device_present() passes?
> >>
> >> That's the biggest issues here. Some driver uses
> >> netif_device_detach() in PM runtime and, this way, introduces custom
> dependency between Core device PM (runtime) sate and Net core, other driver
> does not do.
> >> Does it means every driver with PM runtime now have to be updated to
> indicate it PM state to Net core with netif_device_detach()?
> >
> > No, that's not needed.
> >
> >> Why? Why return value from pm_runtime_get calls is not enough?
> >>
> >> Believe me it's terrible idea to introduce custom PM state dependency
> >> between PM runtime and Net core, for example it took years to sync
> properly System wide suspend and PM runtime which are separate framworks.
> >>
> >> By the way netif_device_detach() during System Wide suspend is looks
> >> perfectly valid, because entering System wide Suspend should prohibit
> >> any access to netdev at some stage. And that's what 99% of network
> >> drivers are doing (actually I can find only ./realtek/r8169_main.c
> >> which abuse netif_device_detach() function and, I assume, it is your
> >> case)
> >>
> > Actually I was inspired by the Intel drivers, see e.g.
> > __igc_shutdown(). They also detach the netdevice on runtime suspend.
> > One reason is that several core functions check for device presence
> > before e.g. calling a ndo callback. Example: dev_set_mtu_ext()
> 
> right and also:
> - netlink - which you've hacked already
> - 8021q:
> vlan_dev_ioctl/vlan_dev_neigh_setup/vlan_add_rx_filter_info/vlan_kill_rx_filte
> r_info

Yes, there are many place need to do such check. I always face a problem that where I need to
runtime-resume the device, is there any suggestion? I always add it when an issue came out.

What confuse me it that, is there any document describe that which .ndo callback should be called
with interface up, instead .ndo callback _CAN_ be called with interface down? I think this can help
us decide when we need runtime-resume device.

After leaning all your discussion, from my point of view, it seems not a good choice to add RPM
to net core. It had better handled by driver itself.
 
> 
> > Same applies for __dev_set_rx_mode(). Therefore I wondered whether
> > cpsw_ndo_set_rx_mode()
> > - that does not include runtime-resuming the device - may be called
> > when device is runtime-suspended, e.g. if interface is up, but link is down.
> 
> CPSW doesn't manage PM runtime in link status handler, as it has only on/off
> state and off state can cause full context loss restore of which is expensive and
> hard to implement. And for most of netdev drivers no aggressive PM runtime is
> implemented exactly because of that (mac/vlan/fdb/mdb/...). Common
> patterns:
> 
> (a)
> .probe
>   -get
> .remove
>   -put
> 
> (b)
> .probe
>   -get
>   -put
> .open
>   -get
> .close
>   -put
> .protect places which may be called when netif is down
> 
> The CPSW follows (b) and so cpsw_ndo_set_rx_mode() can't be called when
> when device is runtime-suspended.
> 
> I assume, some hw like PCI, can have more PM states and in some of them
> keep HW context intact.
> 
> 
> >
> >>> Wouldn't we then need RPM ops for the parent (e.g. PCI) and for
> netdev->dev?
> >>
> >> No. as I know -  netdev->dev can be declared as
> >> pm_runtime_no_callbacks(&adap->dev);
> >> I2C adapter might be a good example to check.
> >>
> >>> E.g. the parent runtime-resume can be triggered by a PCI PME, then
> >>> it would have to resume netdev->dev.
> >>>
> >>>> But, to be honest, I'm not sure adding PM runtime manipulation to
> >>>> the net core is a good idea -
> >>>
> >>> The TI CPSW driver runtime-resumes the device in begin ethtool op
> >>> and suspends it in complete. This pattern is used in more than one
> >>> driver and may be worth being moved to the core.
> >>
> >> I'm not against code refactoring and optimization, but in my opinion
> >> it has to be done right from the beginning or not done at all.
> >>
> >>>
> >>>> at minimum it might be tricky and required very careful approach
> (especially in err path).
> >>>> For example, even in this patch you do not check return value of
> >>>> pm_runtime_get_sync() and in commit bd869245a3dc ("net: core: try to
> runtime-resume detached device in __dev_open") also actualy.
> >>>
> >>> The pm_runtime_get_sync() calls are attempts here. We don't want to
> >>> bail out if a device doesn't support RPM.
> >>
> >> And if 'parent' is not supporting PM runtime - it, as i see, should be handled
> by PM runtime core properly.
> >>
> >> I agree that checking the return code could make sense, but then we
> >> would
> >>> have to be careful which error codes we consider as failed.
> >>
> >> huh. you can't 'try' pm_runtime_get_sync() and then align on
> >> netif_device_present() :(
> >>
> >> might be, some how, it will work for r8169_main, but will not work for
> others.
> >> - no checking pm_runtime_get_sync() err code will cause PM runtime
> >> 'usage_count' leak
> >
> > No. pm_runtime_get_sync() always bumps the usage count, no matter
> whether it fails or not.
> 
> 
> > This makes it easy to deal with this. The problem you describe exists
> > with pm_runtime_resume_and_get(). That's why I wondered whether we
> > should annotate this function as __must_check. See here:
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore
> > .kernel.org%2Flinux-pm%2FCAJZ5v0gps0C2923VqM8876npvhcETsyN%2BajAk
> BKX5k
> >
> f49J0%2BMg%40mail.gmail.com%2FT%2F%23t&amp;data=04%7C01%7Cqiang
> qing.zh
> >
> ang%40nxp.com%7C392a231908da48658f4108d957e9f47c%7C686ea1d3bc2b
> 4c6fa92
> >
> cd99c5c301635%7C0%7C0%7C637637484629499490%7CUnknown%7CTWFpb
> GZsb3d8eyJ
> >
> WIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7
> C1000
> >
> &amp;sdata=lbHf9xDmV7w7QkolIsc%2FdmN%2FPKcOCkb2quaMa1JWI2g%3D
> &amp;rese
> > rved=0
> >
> >> - no checking pm_runtime_get_sync() err may cause to continue( for TI
> >> CPSW for example) with
> >>    device in undefined PM state ("disabled" or "half-enabled") and so crash
> later.
> >>
> > I'd say 95% of rpm callers don't check the return value. I'm not
> > saying this is a good thing, but obviously it doesn't cause relevant harm.
> 
> this is completely wrong assumption as PM errors cause silent stuck, undefined
> behavior or dumps (sometimes delayed) which is terribly hard to root cause.
> 
> yes. many drivers do not check, but over last few years more and more strict
> policies applied to avoid that and in many case no checking return code - is red
> flag and patch reject.
> Don't like that phrase ;), but "It doesn't mean that incorrect code has to be
> copy-pasted all over the places"
> 
> this is correct get pattern for get:
> 	ret = pm_runtime_get_sync(&pdev->dev);
> 	if (ret < 0) {
> 		pm_runtime_put_noidle(&pdev->dev);
> 		return ret;
> 	}

Yes, it’s the correct usage for pm_runtime_get_sync.

Best Regards,
Joakim Zhang
> My strong opinion
>   - PM runtime return code must be checked.
>   - get rid of netif_device_detach() in r8169
> 
> by the way, have you tried below test with your driver (not sure how it works
> for you):
> 
> .rtl_open
>   - pm_runtime_get_sync
>   - pm_runtime_put_sync - usage_count == 0 .r8169_phylink_handler
>   - pm_request_resume - why async? still usage_count == 0 .some ethtool
> request to go through dev_ethtool()
>   - pm_runtime_get_sync
>   - pm_runtime_put - async, usage_count == 0
>     ^ would not it put r8169 in runtime-suspended state while link is still UP?
> 
> 
> >
> >>
> >>
> >>>
> >>>>
> >>>>
> >>>> The TI CPSW driver may also be placed in non reachable state when
> >>>> netdev is closed (and even lose context), but we do not use
> >>>> netif_device_detach() (so netdev is accessible through
> >>>> netdev_ops/ethtool_ops), but instead wake up device by runtime PM for
> allowed operations or just save requested configuration which is applied at
> netdev->open() time then.
> >>>> I feel that using netif_device_detach() in PM runtime sounds like a
> >>>> too heavy approach ;)
> >>>>
> >>> That's not a rare pattern when suspending or runtime-suspending to
> >>> prevent different types of access to a not accessible device. But yes, it's
> relatively big hammer ..
> >>
> >> Again, netif_device_detach() seems correct for System wide suspend,
> >> but in my opinion - it's not correct for PM runtime.
> >>
> >> Sry, with all do respect, first corresponding driver has to be fixed and not
> Net core hacked to support it.
> >>
> >> Further decisions is up to maintainers.
> >>
> >>
> >>>
> >>>> huh, see it's merged already, so...
> >>>>
> >>>>> +
> >>>>> +    if (!netif_device_present(dev)) {
> >>>>> +        rc = -ENODEV;
> >>>>> +        goto out;
> >>>>> +    }
> >>>>> +
> >>>>>         if (dev->ethtool_ops->begin) {
> >>>>>             rc = dev->ethtool_ops->begin(dev);
> >>>>> -        if (rc  < 0)
> >>>>> -            return rc;
> >>>>> +        if (rc < 0)
> >>>>> +            goto out;
> >>>>>         }
> >>>>>         old_features = dev->features;
> >>>>>     @@ -2867,6 +2876,9 @@ int dev_ethtool(struct net *net, struct
> >>>>> ifreq *ifr)
> >>>>>           if (old_features != dev->features)
> >>>>>             netdev_features_change(dev);
> >>>>> +out:
> >>>>> +    if (dev->dev.parent)
> >>>>> +        pm_runtime_put(dev->dev.parent);
> >>>>>           return rc;
> >>>>>     }
> >>>>>
> >>>>
> >>>
> >>
> >
> 
> --
> Best regards,
> grygorii

Re: [PATCH net-next 1/4] ethtool: runtime-resume netdev parent before ethtool ioctl ops

[Grygorii Strashko]

On 05/08/2021 14:11, Joakim Zhang wrote:
> 
>> -----Original Message-----
>> From: Grygorii Strashko <grygorii.strashko@ti.com>
>> Sent: 2021年8月5日 16:21
>> To: Heiner Kallweit <hkallweit1@gmail.com>; Jakub Kicinski
>> <kuba@kernel.org>; David Miller <davem@davemloft.net>
>> Cc: netdev@vger.kernel.org; Linux PM list <linux-pm@vger.kernel.org>;
>> Andrew Lunn <andrew@lunn.ch>; Florian Fainelli <f.fainelli@gmail.com>
>> Subject: Re: [PATCH net-next 1/4] ethtool: runtime-resume netdev parent
>> before ethtool ioctl ops
>>
>>
>>
>> On 04/08/2021 22:33, Heiner Kallweit wrote:
>>> On 04.08.2021 10:43, Grygorii Strashko wrote:
>>>>
>>>>
>>>> On 04/08/2021 00:32, Heiner Kallweit wrote:
>>>>> On 03.08.2021 22:41, Grygorii Strashko wrote:
>>>>>>
>>>>>>
>>>>>> On 01/08/2021 13:36, Heiner Kallweit wrote:
>>>>>>> If a network device is runtime-suspended then:
>>>>>>> - network device may be flagged as detached and all ethtool ops
>>>>>>> (even if not
>>>>>>>       accessing the device) will fail because
>>>>>>> netif_device_present() returns
>>>>>>>       false
>>>>>>> - ethtool ops may fail because device is not accessible (e.g.
>>>>>>> because being
>>>>>>>       in D3 in case of a PCI device)
>>>>>>>
>>>>>>> It may not be desirable that userspace can't use even simple
>>>>>>> ethtool ops that not access the device if interface or link is
>>>>>>> down. To be more friendly to userspace let's ensure that device is
>>>>>>> runtime-resumed when executing the respective ethtool op in kernel.
>>>>>>>
>>>>>>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>>>>>>> ---
>>>>>>>      net/ethtool/ioctl.c | 18 +++++++++++++++---
>>>>>>>      1 file changed, 15 insertions(+), 3 deletions(-)
>>>>>>>
>>>>>>> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c index
>>>>>>> baa5d1004..b7ff9abe7 100644
>>>>>>> --- a/net/ethtool/ioctl.c
>>>>>>> +++ b/net/ethtool/ioctl.c
>>>>>>> @@ -23,6 +23,7 @@
>>>>>>>      #include <linux/rtnetlink.h>
>>>>>>>      #include <linux/sched/signal.h>
>>>>>>>      #include <linux/net.h>
>>>>>>> +#include <linux/pm_runtime.h>
>>>>>>>      #include <net/devlink.h>
>>>>>>>      #include <net/xdp_sock_drv.h>
>>>>>>>      #include <net/flow_offload.h>
>>>>>>> @@ -2589,7 +2590,7 @@ int dev_ethtool(struct net *net, struct
>>>>>>> ifreq *ifr)
>>>>>>>          int rc;
>>>>>>>          netdev_features_t old_features;
>>>>>>>      -    if (!dev || !netif_device_present(dev))
>>>>>>> +    if (!dev)
>>>>>>>              return -ENODEV;
>>>>>>>            if (copy_from_user(&ethcmd, useraddr, sizeof(ethcmd)))
>>>>>>> @@ -2645,10 +2646,18 @@ int dev_ethtool(struct net *net, struct
>>>>>>> ifreq *ifr)
>>>>>>>                  return -EPERM;
>>>>>>>          }
>>>>>>>      +    if (dev->dev.parent)
>>>>>>> +        pm_runtime_get_sync(dev->dev.parent);
>>>>>>
>>>>>> the PM Runtime should allow to wake up parent when child is resumed if
>> everything is configured properly.
>>>>>>
>>>>> Not sure if there's any case yet where the netdev-embedded device is
>> power-managed.
>>>>> Typically only the parent (e.g. a PCI device) is.
>>>>>
>>>>>> rpm_resume()
>>>>>> ...
>>>>>>        if (!parent && dev->parent) {
>>>>>>     --> here
>>>>>>
>>>>> Currently we don't get that far because we will bail out here already:
>>>>>
>>>>> else if (dev->power.disable_depth > 0)
>>>>>           retval = -EACCES;
>>>>>
>>>>> If netdev-embedded device isn't power-managed then disable_depth is 1.
>>>>
>>>> Right. But if pm_runtime_enable() is added for ndev->dev then PM
>>>> runtime will start working for it and should handle parent properly -
>>>> from my experience, every time any code need manipulate with "parent" or
>> smth. else to make PM runtime working it means smth. is wrong.
>>>>
>>>> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c index
>>>> f6197774048b..33b72b788aa2 100644
>>>> --- a/net/core/net-sysfs.c
>>>> +++ b/net/core/net-sysfs.c
>>>> @@ -1963,6 +1963,7 @@ int netdev_register_kobject(struct net_device
>>>> *ndev)
>>>>           }
>>>>
>>>>           pm_runtime_set_memalloc_noio(dev, true);
>>>> +       pm_runtime_enable(dev);
>>>>
>>>>           return error;
>>>>    }
>>>>
>>>>
>>>>>
>>>>>> So, hence PM runtime calls are moved to from drivers to net_core
>>>>>> wouldn't be more correct approach to enable PM runtime for netdev->dev
>> and lets PM runtime do the job?
>>>>>>
>>>>> Where would netdev->dev be runtime-resumed so that
>> netif_device_present() passes?
>>>>
>>>> That's the biggest issues here. Some driver uses
>>>> netif_device_detach() in PM runtime and, this way, introduces custom
>> dependency between Core device PM (runtime) sate and Net core, other driver
>> does not do.
>>>> Does it means every driver with PM runtime now have to be updated to
>> indicate it PM state to Net core with netif_device_detach()?
>>>
>>> No, that's not needed.
>>>
>>>> Why? Why return value from pm_runtime_get calls is not enough?
>>>>
>>>> Believe me it's terrible idea to introduce custom PM state dependency
>>>> between PM runtime and Net core, for example it took years to sync
>> properly System wide suspend and PM runtime which are separate framworks.
>>>>
>>>> By the way netif_device_detach() during System Wide suspend is looks
>>>> perfectly valid, because entering System wide Suspend should prohibit
>>>> any access to netdev at some stage. And that's what 99% of network
>>>> drivers are doing (actually I can find only ./realtek/r8169_main.c
>>>> which abuse netif_device_detach() function and, I assume, it is your
>>>> case)
>>>>
>>> Actually I was inspired by the Intel drivers, see e.g.
>>> __igc_shutdown(). They also detach the netdevice on runtime suspend.
>>> One reason is that several core functions check for device presence
>>> before e.g. calling a ndo callback. Example: dev_set_mtu_ext()
>>
>> right and also:
>> - netlink - which you've hacked already
>> - 8021q:
>> vlan_dev_ioctl/vlan_dev_neigh_setup/vlan_add_rx_filter_info/vlan_kill_rx_filte
>> r_info
> 
> Yes, there are many place need to do such check. I always face a problem that where I need to
> runtime-resume the device, is there any suggestion? I always add it when an issue came out.
> 
> What confuse me it that, is there any document describe that which .ndo callback should be called
> with interface up, instead .ndo callback _CAN_ be called with interface down? I think this can help
> us decide when we need runtime-resume device.

In general, you can assume that any ndo can be called which are not part of data path (xmit, watchdog, irq/napi),
so the only option is to put netif down and go through every ndo testing.

> 
> After leaning all your discussion, from my point of view, it seems not a good choice to add RPM
> to net core. It had better handled by driver itself.


-- 
Best regards,
grygorii

Re: [PATCH net-next 1/4] ethtool: runtime-resume netdev parent before ethtool ioctl ops

[Heiner Kallweit]

On 05.08.2021 10:20, Grygorii Strashko wrote:
> 
> 
> On 04/08/2021 22:33, Heiner Kallweit wrote:
>> On 04.08.2021 10:43, Grygorii Strashko wrote:
>>>
>>>
>>> On 04/08/2021 00:32, Heiner Kallweit wrote:
>>>> On 03.08.2021 22:41, Grygorii Strashko wrote:
>>>>>
>>>>>
>>>>> On 01/08/2021 13:36, Heiner Kallweit wrote:
>>>>>> If a network device is runtime-suspended then:
>>>>>> - network device may be flagged as detached and all ethtool ops (even if not
>>>>>>      accessing the device) will fail because netif_device_present() returns
>>>>>>      false
>>>>>> - ethtool ops may fail because device is not accessible (e.g. because being
>>>>>>      in D3 in case of a PCI device)
>>>>>>
>>>>>> It may not be desirable that userspace can't use even simple ethtool ops
>>>>>> that not access the device if interface or link is down. To be more friendly
>>>>>> to userspace let's ensure that device is runtime-resumed when executing the
>>>>>> respective ethtool op in kernel.
>>>>>>
>>>>>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>>>>>> ---
>>>>>>     net/ethtool/ioctl.c | 18 +++++++++++++++---
>>>>>>     1 file changed, 15 insertions(+), 3 deletions(-)
>>>>>>
>>>>>> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
>>>>>> index baa5d1004..b7ff9abe7 100644
>>>>>> --- a/net/ethtool/ioctl.c
>>>>>> +++ b/net/ethtool/ioctl.c
>>>>>> @@ -23,6 +23,7 @@
>>>>>>     #include <linux/rtnetlink.h>
>>>>>>     #include <linux/sched/signal.h>
>>>>>>     #include <linux/net.h>
>>>>>> +#include <linux/pm_runtime.h>
>>>>>>     #include <net/devlink.h>
>>>>>>     #include <net/xdp_sock_drv.h>
>>>>>>     #include <net/flow_offload.h>
>>>>>> @@ -2589,7 +2590,7 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>>>>>         int rc;
>>>>>>         netdev_features_t old_features;
>>>>>>     -    if (!dev || !netif_device_present(dev))
>>>>>> +    if (!dev)
>>>>>>             return -ENODEV;
>>>>>>           if (copy_from_user(&ethcmd, useraddr, sizeof(ethcmd)))
>>>>>> @@ -2645,10 +2646,18 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>>>>>                 return -EPERM;
>>>>>>         }
>>>>>>     +    if (dev->dev.parent)
>>>>>> +        pm_runtime_get_sync(dev->dev.parent);
>>>>>
>>>>> the PM Runtime should allow to wake up parent when child is resumed if everything is configured properly.
>>>>>
>>>> Not sure if there's any case yet where the netdev-embedded device is power-managed.
>>>> Typically only the parent (e.g. a PCI device) is.
>>>>
>>>>> rpm_resume()
>>>>> ...
>>>>>       if (!parent && dev->parent) {
>>>>>    --> here
>>>>>
>>>> Currently we don't get that far because we will bail out here already:
>>>>
>>>> else if (dev->power.disable_depth > 0)
>>>>          retval = -EACCES;
>>>>
>>>> If netdev-embedded device isn't power-managed then disable_depth is 1.
>>>
>>> Right. But if pm_runtime_enable() is added for ndev->dev then PM runtime will start working for it
>>> and should handle parent properly - from my experience, every time any code need manipulate with "parent" or
>>> smth. else to make PM runtime working it means smth. is wrong.
>>>
>>> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
>>> index f6197774048b..33b72b788aa2 100644
>>> --- a/net/core/net-sysfs.c
>>> +++ b/net/core/net-sysfs.c
>>> @@ -1963,6 +1963,7 @@ int netdev_register_kobject(struct net_device *ndev)
>>>          }
>>>            pm_runtime_set_memalloc_noio(dev, true);
>>> +       pm_runtime_enable(dev);
>>>            return error;
>>>   }
>>>
>>>
>>>>
>>>>> So, hence PM runtime calls are moved to from drivers to net_core wouldn't be more correct approach to
>>>>> enable PM runtime for netdev->dev and lets PM runtime do the job?
>>>>>
>>>> Where would netdev->dev be runtime-resumed so that netif_device_present() passes?
>>>
>>> That's the biggest issues here. Some driver uses netif_device_detach() in PM runtime and, this way, introduces custom dependency
>>> between Core device PM (runtime) sate and Net core, other driver does not do.
>>> Does it means every driver with PM runtime now have to be updated to indicate it PM state to Net core with netif_device_detach()?
>>
>> No, that's not needed.
>>
>>> Why? Why return value from pm_runtime_get calls is not enough?
>>>
>>> Believe me it's terrible idea to introduce custom PM state dependency between PM runtime and Net core,
>>> for example it took years to sync properly System wide suspend and PM runtime which are separate framworks.
>>>
>>> By the way netif_device_detach() during System Wide suspend is looks perfectly valid, because entering
>>> System wide Suspend should prohibit any access to netdev at some stage. And that's what 99% of network drivers are doing
>>> (actually I can find only ./realtek/r8169_main.c which abuse netif_device_detach() function and,
>>> I assume, it is your case)
>>>
>> Actually I was inspired by the Intel drivers, see e.g. __igc_shutdown(). They also detach the
>> netdevice on runtime suspend. One reason is that several core functions check for device
>> presence before e.g. calling a ndo callback. Example: dev_set_mtu_ext()
> 
> right and also:
> - netlink - which you've hacked already
> - 8021q: vlan_dev_ioctl/vlan_dev_neigh_setup/vlan_add_rx_filter_info/vlan_kill_rx_filter_info
> 
> 
>> Same applies for __dev_set_rx_mode(). Therefore I wondered whether cpsw_ndo_set_rx_mode()
>> - that does not include runtime-resuming the device - may be called when device is
>> runtime-suspended, e.g. if interface is up, but link is down.
> 
> CPSW doesn't manage PM runtime in link status handler, as it has only on/off state and off state can cause full
> context loss restore of which is expensive and hard to implement. And for most of netdev drivers no aggressive PM runtime
> is implemented exactly because of that (mac/vlan/fdb/mdb/...). Common patterns:
> 
> (a)
> .probe
>  -get
> .remove
>  -put
> 
> (b)
> .probe
>  -get
>  -put
> .open
>  -get
> .close
>  -put
> .protect places which may be called when netif is down
> 
> The CPSW follows (b) and so cpsw_ndo_set_rx_mode() can't be called when when device is
> runtime-suspended.
> 
> I assume, some hw like PCI, can have more PM states and in some of them keep HW context intact.
> 
Exactly, there's no reason to keep PCI in D0 if link is down. Once NIC detects a cable was
plugged in it triggers a PCI PME and PCI core sets PCI bus from D3cold/D3hot to D0 and
runtime-resumes device.

> 
>>
>>>> Wouldn't we then need RPM ops for the parent (e.g. PCI) and for netdev->dev?
>>>
>>> No. as I know -  netdev->dev can be declared as pm_runtime_no_callbacks(&adap->dev);
>>> I2C adapter might be a good example to check.
>>>
>>>> E.g. the parent runtime-resume can be triggered by a PCI PME, then it would
>>>> have to resume netdev->dev.
>>>>
>>>>> But, to be honest, I'm not sure adding PM runtime manipulation to the net core is a good idea -
>>>>
>>>> The TI CPSW driver runtime-resumes the device in begin ethtool op and suspends
>>>> it in complete. This pattern is used in more than one driver and may be worth
>>>> being moved to the core.
>>>
>>> I'm not against code refactoring and optimization, but in my opinion it has to be done right from the beginning or
>>> not done at all.
>>>
>>>>
>>>>> at minimum it might be tricky and required very careful approach (especially in err path).
>>>>> For example, even in this patch you do not check return value of pm_runtime_get_sync() and in
>>>>> commit bd869245a3dc ("net: core: try to runtime-resume detached device in __dev_open") also actualy.
>>>>
>>>> The pm_runtime_get_sync() calls are attempts here. We don't want to bail out if a device
>>>> doesn't support RPM.
>>>
>>> And if 'parent' is not supporting PM runtime - it, as i see, should be handled by PM runtime core properly.
>>>
>>> I agree that checking the return code could make sense, but then we would
>>>> have to be careful which error codes we consider as failed.
>>>
>>> huh. you can't 'try' pm_runtime_get_sync() and then align on netif_device_present() :(
>>>
>>> might be, some how, it will work for r8169_main, but will not work for others.
>>> - no checking pm_runtime_get_sync() err code will cause PM runtime 'usage_count' leak
>>
>> No. pm_runtime_get_sync() always bumps the usage count, no matter whether it fails or not.
> 
> 
>> This makes it easy to deal with this. The problem you describe exists with
>> pm_runtime_resume_and_get(). That's why I wondered whether we should annotate this
>> function as __must_check. See here:
>> https://lore.kernel.org/linux-pm/CAJZ5v0gps0C2923VqM8876npvhcETsyN+ajAkBKX5kf49J0+Mg@mail.gmail.com/T/#t
>>
>>> - no checking pm_runtime_get_sync() err may cause to continue( for TI CPSW for example) with
>>>    device in undefined PM state ("disabled" or "half-enabled") and so crash later.
>>>
>> I'd say 95% of rpm callers don't check the return value. I'm not saying this is a good thing,
>> but obviously it doesn't cause relevant harm.
> 
> this is completely wrong assumption as PM errors cause silent stuck, undefined behavior or dumps (sometimes delayed)
> which is terribly hard to root cause.
> 
> yes. many drivers do not check, but over last few years more and more strict policies applied to avoid that and
> in many case no checking return code - is red flag and patch reject.
> Don't like that phrase ;), but "It doesn't mean that incorrect code has to be copy-pasted all over the places"
> 
> this is correct get pattern for get:
>     ret = pm_runtime_get_sync(&pdev->dev);
>     if (ret < 0) {
>         pm_runtime_put_noidle(&pdev->dev);
>         return ret;
>     }
> 
That's exactly what pm_runtime_resume_and_get() does. IIRC this helper hasn't been
part of the API from the beginning and was added later.

> My strong opinion
>  - PM runtime return code must be checked.
>  - get rid of netif_device_detach() in r8169
> 
> by the way, have you tried below test with your driver (not sure how it works for you):
> 
> .rtl_open
>  - pm_runtime_get_sync
>  - pm_runtime_put_sync - usage_count == 0
> .r8169_phylink_handler
>  - pm_request_resume - why async? still usage_count == 0

pm_request_resume() is only meant to cancel a potentially scheduled runtime-suspend
if link has a short drop. In such a case link would be up again after ~ 3-4s,
timeout for runtime-suspending device after link drop is 10s.

> .some ethtool request to go through dev_ethtool()
>  - pm_runtime_get_sync
>  - pm_runtime_put - async, usage_count == 0
>    ^ would not it put r8169 in runtime-suspended state while link is still UP?
>  
No, see rtl8169_runtime_idle(). If link is up no runtime suspend is scheduled.

> 
>>
>>>
>>>
>>>>
>>>>>
>>>>>
>>>>> The TI CPSW driver may also be placed in non reachable state when netdev is closed (and even lose context),
>>>>> but we do not use netif_device_detach() (so netdev is accessible through netdev_ops/ethtool_ops),
>>>>> but instead wake up device by runtime PM for allowed operations or just save requested configuration which
>>>>> is applied at netdev->open() time then.
>>>>> I feel that using netif_device_detach() in PM runtime sounds like a too heavy approach ;)
>>>>>
>>>> That's not a rare pattern when suspending or runtime-suspending to prevent different types
>>>> of access to a not accessible device. But yes, it's relatively big hammer ..
>>>
>>> Again, netif_device_detach() seems correct for System wide suspend, but in my opinion - it's
>>> not correct for PM runtime.
>>>
>>> Sry, with all do respect, first corresponding driver has to be fixed and not Net core hacked to support it.
>>>
>>> Further decisions is up to maintainers.
>>>
>>>
>>>>
>>>>> huh, see it's merged already, so...
>>>>>
>>>>>> +
>>>>>> +    if (!netif_device_present(dev)) {
>>>>>> +        rc = -ENODEV;
>>>>>> +        goto out;
>>>>>> +    }
>>>>>> +
>>>>>>         if (dev->ethtool_ops->begin) {
>>>>>>             rc = dev->ethtool_ops->begin(dev);
>>>>>> -        if (rc  < 0)
>>>>>> -            return rc;
>>>>>> +        if (rc < 0)
>>>>>> +            goto out;
>>>>>>         }
>>>>>>         old_features = dev->features;
>>>>>>     @@ -2867,6 +2876,9 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>>>>>           if (old_features != dev->features)
>>>>>>             netdev_features_change(dev);
>>>>>> +out:
>>>>>> +    if (dev->dev.parent)
>>>>>> +        pm_runtime_put(dev->dev.parent);
>>>>>>           return rc;
>>>>>>     }
>>>>>>
>>>>>
>>>>
>>>
>>
> 

Re: [PATCH net-next 1/4] ethtool: runtime-resume netdev parent before ethtool ioctl ops

[Grygorii Strashko]

On 05/08/2021 22:24, Heiner Kallweit wrote:
> On 05.08.2021 10:20, Grygorii Strashko wrote:
>>
>>
>> On 04/08/2021 22:33, Heiner Kallweit wrote:
>>> On 04.08.2021 10:43, Grygorii Strashko wrote:
>>>>
>>>>
>>>> On 04/08/2021 00:32, Heiner Kallweit wrote:
>>>>> On 03.08.2021 22:41, Grygorii Strashko wrote:
>>>>>>
>>>>>>
>>>>>> On 01/08/2021 13:36, Heiner Kallweit wrote:
>>>>>>> If a network device is runtime-suspended then:
>>>>>>> - network device may be flagged as detached and all ethtool ops (even if not
>>>>>>>       accessing the device) will fail because netif_device_present() returns
>>>>>>>       false
>>>>>>> - ethtool ops may fail because device is not accessible (e.g. because being
>>>>>>>       in D3 in case of a PCI device)
>>>>>>>
>>>>>>> It may not be desirable that userspace can't use even simple ethtool ops
>>>>>>> that not access the device if interface or link is down. To be more friendly
>>>>>>> to userspace let's ensure that device is runtime-resumed when executing the
>>>>>>> respective ethtool op in kernel.
>>>>>>>
>>>>>>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>>>>>>> ---
>>>>>>>      net/ethtool/ioctl.c | 18 +++++++++++++++---
>>>>>>>      1 file changed, 15 insertions(+), 3 deletions(-)
>>>>>>>
>>>>>>> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
>>>>>>> index baa5d1004..b7ff9abe7 100644
>>>>>>> --- a/net/ethtool/ioctl.c
>>>>>>> +++ b/net/ethtool/ioctl.c
>>>>>>> @@ -23,6 +23,7 @@
>>>>>>>      #include <linux/rtnetlink.h>
>>>>>>>      #include <linux/sched/signal.h>
>>>>>>>      #include <linux/net.h>
>>>>>>> +#include <linux/pm_runtime.h>
>>>>>>>      #include <net/devlink.h>
>>>>>>>      #include <net/xdp_sock_drv.h>
>>>>>>>      #include <net/flow_offload.h>
>>>>>>> @@ -2589,7 +2590,7 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>>>>>>          int rc;
>>>>>>>          netdev_features_t old_features;
>>>>>>>      -    if (!dev || !netif_device_present(dev))
>>>>>>> +    if (!dev)
>>>>>>>              return -ENODEV;
>>>>>>>            if (copy_from_user(&ethcmd, useraddr, sizeof(ethcmd)))
>>>>>>> @@ -2645,10 +2646,18 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>>>>>>                  return -EPERM;
>>>>>>>          }
>>>>>>>      +    if (dev->dev.parent)
>>>>>>> +        pm_runtime_get_sync(dev->dev.parent);
>>>>>>
>>>>>> the PM Runtime should allow to wake up parent when child is resumed if everything is configured properly.
>>>>>>
>>>>> Not sure if there's any case yet where the netdev-embedded device is power-managed.
>>>>> Typically only the parent (e.g. a PCI device) is.
>>>>>
>>>>>> rpm_resume()
>>>>>> ...
>>>>>>        if (!parent && dev->parent) {
>>>>>>     --> here
>>>>>>
>>>>> Currently we don't get that far because we will bail out here already:
>>>>>
>>>>> else if (dev->power.disable_depth > 0)
>>>>>           retval = -EACCES;
>>>>>
>>>>> If netdev-embedded device isn't power-managed then disable_depth is 1.
>>>>
>>>> Right. But if pm_runtime_enable() is added for ndev->dev then PM runtime will start working for it
>>>> and should handle parent properly - from my experience, every time any code need manipulate with "parent" or
>>>> smth. else to make PM runtime working it means smth. is wrong.
>>>>
>>>> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
>>>> index f6197774048b..33b72b788aa2 100644
>>>> --- a/net/core/net-sysfs.c
>>>> +++ b/net/core/net-sysfs.c
>>>> @@ -1963,6 +1963,7 @@ int netdev_register_kobject(struct net_device *ndev)
>>>>           }
>>>>             pm_runtime_set_memalloc_noio(dev, true);
>>>> +       pm_runtime_enable(dev);
>>>>             return error;
>>>>    }
>>>>
>>>>
>>>>>
>>>>>> So, hence PM runtime calls are moved to from drivers to net_core wouldn't be more correct approach to
>>>>>> enable PM runtime for netdev->dev and lets PM runtime do the job?
>>>>>>
>>>>> Where would netdev->dev be runtime-resumed so that netif_device_present() passes?
>>>>
>>>> That's the biggest issues here. Some driver uses netif_device_detach() in PM runtime and, this way, introduces custom dependency
>>>> between Core device PM (runtime) sate and Net core, other driver does not do.
>>>> Does it means every driver with PM runtime now have to be updated to indicate it PM state to Net core with netif_device_detach()?
>>>
>>> No, that's not needed.
>>>
>>>> Why? Why return value from pm_runtime_get calls is not enough?
>>>>
>>>> Believe me it's terrible idea to introduce custom PM state dependency between PM runtime and Net core,
>>>> for example it took years to sync properly System wide suspend and PM runtime which are separate framworks.
>>>>
>>>> By the way netif_device_detach() during System Wide suspend is looks perfectly valid, because entering
>>>> System wide Suspend should prohibit any access to netdev at some stage. And that's what 99% of network drivers are doing
>>>> (actually I can find only ./realtek/r8169_main.c which abuse netif_device_detach() function and,
>>>> I assume, it is your case)
>>>>
>>> Actually I was inspired by the Intel drivers, see e.g. __igc_shutdown(). They also detach the
>>> netdevice on runtime suspend. One reason is that several core functions check for device
>>> presence before e.g. calling a ndo callback. Example: dev_set_mtu_ext()
>>
>> right and also:
>> - netlink - which you've hacked already
>> - 8021q: vlan_dev_ioctl/vlan_dev_neigh_setup/vlan_add_rx_filter_info/vlan_kill_rx_filter_info
>>
>>
>>> Same applies for __dev_set_rx_mode(). Therefore I wondered whether cpsw_ndo_set_rx_mode()
>>> - that does not include runtime-resuming the device - may be called when device is
>>> runtime-suspended, e.g. if interface is up, but link is down.
>>
>> CPSW doesn't manage PM runtime in link status handler, as it has only on/off state and off state can cause full
>> context loss restore of which is expensive and hard to implement. And for most of netdev drivers no aggressive PM runtime
>> is implemented exactly because of that (mac/vlan/fdb/mdb/...). Common patterns:
>>
>> (a)
>> .probe
>>   -get
>> .remove
>>   -put
>>
>> (b)
>> .probe
>>   -get
>>   -put
>> .open
>>   -get
>> .close
>>   -put
>> .protect places which may be called when netif is down
>>
>> The CPSW follows (b) and so cpsw_ndo_set_rx_mode() can't be called when when device is
>> runtime-suspended.
>>
>> I assume, some hw like PCI, can have more PM states and in some of them keep HW context intact.
>>
> Exactly, there's no reason to keep PCI in D0 if link is down. Once NIC detects a cable was
> plugged in it triggers a PCI PME and PCI core sets PCI bus from D3cold/D3hot to D0 and
> runtime-resumes device.
> 
>>
>>>
>>>>> Wouldn't we then need RPM ops for the parent (e.g. PCI) and for netdev->dev?
>>>>
>>>> No. as I know -  netdev->dev can be declared as pm_runtime_no_callbacks(&adap->dev);
>>>> I2C adapter might be a good example to check.
>>>>
>>>>> E.g. the parent runtime-resume can be triggered by a PCI PME, then it would
>>>>> have to resume netdev->dev.
>>>>>
>>>>>> But, to be honest, I'm not sure adding PM runtime manipulation to the net core is a good idea -
>>>>>
>>>>> The TI CPSW driver runtime-resumes the device in begin ethtool op and suspends
>>>>> it in complete. This pattern is used in more than one driver and may be worth
>>>>> being moved to the core.
>>>>
>>>> I'm not against code refactoring and optimization, but in my opinion it has to be done right from the beginning or
>>>> not done at all.
>>>>
>>>>>
>>>>>> at minimum it might be tricky and required very careful approach (especially in err path).
>>>>>> For example, even in this patch you do not check return value of pm_runtime_get_sync() and in
>>>>>> commit bd869245a3dc ("net: core: try to runtime-resume detached device in __dev_open") also actualy.
>>>>>
>>>>> The pm_runtime_get_sync() calls are attempts here. We don't want to bail out if a device
>>>>> doesn't support RPM.
>>>>
>>>> And if 'parent' is not supporting PM runtime - it, as i see, should be handled by PM runtime core properly.
>>>>
>>>> I agree that checking the return code could make sense, but then we would
>>>>> have to be careful which error codes we consider as failed.
>>>>
>>>> huh. you can't 'try' pm_runtime_get_sync() and then align on netif_device_present() :(
>>>>
>>>> might be, some how, it will work for r8169_main, but will not work for others.
>>>> - no checking pm_runtime_get_sync() err code will cause PM runtime 'usage_count' leak
>>>
>>> No. pm_runtime_get_sync() always bumps the usage count, no matter whether it fails or not.
>>
>>
>>> This makes it easy to deal with this. The problem you describe exists with
>>> pm_runtime_resume_and_get(). That's why I wondered whether we should annotate this
>>> function as __must_check. See here:
>>> https://lore.kernel.org/linux-pm/CAJZ5v0gps0C2923VqM8876npvhcETsyN+ajAkBKX5kf49J0+Mg@mail.gmail.com/T/#t
>>>
>>>> - no checking pm_runtime_get_sync() err may cause to continue( for TI CPSW for example) with
>>>>     device in undefined PM state ("disabled" or "half-enabled") and so crash later.
>>>>
>>> I'd say 95% of rpm callers don't check the return value. I'm not saying this is a good thing,
>>> but obviously it doesn't cause relevant harm.
>>
>> this is completely wrong assumption as PM errors cause silent stuck, undefined behavior or dumps (sometimes delayed)
>> which is terribly hard to root cause.
>>
>> yes. many drivers do not check, but over last few years more and more strict policies applied to avoid that and
>> in many case no checking return code - is red flag and patch reject.
>> Don't like that phrase ;), but "It doesn't mean that incorrect code has to be copy-pasted all over the places"
>>
>> this is correct get pattern for get:
>>      ret = pm_runtime_get_sync(&pdev->dev);
>>      if (ret < 0) {
>>          pm_runtime_put_noidle(&pdev->dev);
>>          return ret;
>>      }
>>
> That's exactly what pm_runtime_resume_and_get() does. IIRC this helper hasn't been
> part of the API from the beginning and was added later.
> 
>> My strong opinion
>>   - PM runtime return code must be checked.
>>   - get rid of netif_device_detach() in r8169
>>
>> by the way, have you tried below test with your driver (not sure how it works for you):
>>
>> .rtl_open
>>   - pm_runtime_get_sync
>>   - pm_runtime_put_sync - usage_count == 0
>> .r8169_phylink_handler
>>   - pm_request_resume - why async? still usage_count == 0
> 
> pm_request_resume() is only meant to cancel a potentially scheduled runtime-suspend
> if link has a short drop. In such a case link would be up again after ~ 3-4s,
> timeout for runtime-suspending device after link drop is 10s.
> 
>> .some ethtool request to go through dev_ethtool()
>>   - pm_runtime_get_sync
>>   - pm_runtime_put - async, usage_count == 0
>>     ^ would not it put r8169 in runtime-suspended state while link is still UP?
>>   
> No, see rtl8169_runtime_idle(). If link is up no runtime suspend is scheduled.

really :) This one

static int rtl8169_runtime_idle(struct device *device)
{
	struct rtl8169_private *tp = dev_get_drvdata(device);

	if (!netif_running(tp->dev) || !netif_carrier_ok(tp->dev))
		pm_schedule_suspend(device, 10000);

	return -EBUSY;
}

Sry, but you really need to take pause and rump up on PM runtime, with all do respect.

Pay attention on PM runtime autosupend, so you can do properly get_sync on link up and use autosuspend on Link down.

Hope PM people can comment here also.

-- 
Best regards,
grygorii