netdev - Re: [PATCH] net:phy fix driver reference count error when attach and detach phy device

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Date:   Mon, 12 Dec 2016 16:49:25 +0800
From:   maowenan <maowenan@...wei.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "dingtianhong@...wei.com" <dingtianhong@...wei.com>,
        "weiyongjun (A)" <weiyongjun1@...wei.com>
Subject: Re: [PATCH] net:phy fix driver reference count error when attach and
 detach phy device



On 2016/12/5 16:47, maowenan wrote:
> 
> 
> On 2016/12/2 17:45, David Laight wrote:
>> From: Mao Wenan
>>> Sent: 30 November 2016 10:23
>>> The nic in my board use the phy dev from marvell, and the system will
>>> load the marvell phy driver automatically, but when I remove the phy
>>> drivers, the system immediately panic:
>>> Call trace:
>>> [ 2582.834493] [<ffff800000715384>] phy_state_machine+0x3c/0x438 [
>>> 2582.851754] [<ffff8000000db3b8>] process_one_work+0x150/0x428 [
>>> 2582.868188] [<ffff8000000db7d4>] worker_thread+0x144/0x4b0 [
>>> 2582.883882] [<ffff8000000e1d0c>] kthread+0xfc/0x110
>>>
>>> there should be proper reference counting in place to avoid that.
>>> I found that phy_attach_direct() forgets to add phy device driver
>>> reference count, and phy_detach() forgets to subtract reference count.
>>> This patch is to fix this bug, after that panic is disappeared when remove
>>> marvell.ko
>>>
>>> Signed-off-by: Mao Wenan <maowenan@...wei.com>
>>> ---
>>>  drivers/net/phy/phy_device.c | 7 +++++++
>>>  1 file changed, 7 insertions(+)
>>>
>>> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
>>> index 1a4bf8a..a7ec7c2 100644
>>> --- a/drivers/net/phy/phy_device.c
>>> +++ b/drivers/net/phy/phy_device.c
>>> @@ -866,6 +866,11 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
>>>  		return -EIO;
>>>  	}
>>>
>>> +	if (!try_module_get(d->driver->owner)) {
>>> +		dev_err(&dev->dev, "failed to get the device driver module\n");
>>> +		return -EIO;
>>> +	}
>>
>> If this is the phy code, what stops the phy driver being unloaded
>> before the try_module_get() obtains a reference.
>> If it isn't the phy driver then there ought to be a reference count obtained
>> when the phy driver is located (by whatever decides which phy driver to use).
>> Even if that code later releases its reference (it probably shouldn't on success)
>> then you can't fail to get an extra reference here.
> 
> [Mao Wenan]Yes, this is phy code, in function phy_attach_direct(), drivers/net/phy/phy_device.c.
> when one NIC driver to do probe behavior, it will attach one matched phy driver. phy_attach_direct()
> is to obtain phy driver reference and bind phy driver, if try_module_get() execute on success, the reference
> count is added; if failed, the driver can't be attached to this NIC, and it can't added the phy driver
> reference count. So before try_module_get obtains a reference, phy driver can't can't be bound to this NIC.
> when the phy driver is attached to NIC, the reference count is added, if someone remove phy driver directly,
> it will be failed because reference count is not equal to 0.
> 
> An example of call trace when there is NIC driver to attch one phy driver:
> hns_nic_dev_probe->hns_nic_try_get_ae->hns_nic_init_phy->of_phy_connect->phy_connect_direct->phy_attach_direct
> 
> Consider the steps of phy driver(marvell.ko) added and removed, and NIC driver(hns_enet_drv.ko) added and removed:
> 1)insmod marvell       ref=0
> 2)insmod hns_enet_drv  ref=1
> 3)rmmod marvell        (should not on success, ref=1)
> 4)rmmod hns_enet_drv   ref=0
> 5)rmmod marvell        (should on success, because ref=0)
> 
> if we don't add the reference count in phy_attach_direct(the second step ref=0), so the third step rmmod marvell will
> be panic, because there is one user remain use marvell driver and phy_stat_machine use the NULL drv pointer.
> 
>>
>>> +
>>>  	get_device(d);
>>>
>>>  	/* Assume that if there is no driver, that it doesn't
>>> @@ -921,6 +926,7 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
>>>
>>>  error:
>>>  	put_device(d);
>>> +	module_put(d->driver->owner);
>>
>> Are those two in the wrong order ?
>>
>>>  	module_put(bus->owner);
>>>  	return err;
>>>  }
>>> @@ -998,6 +1004,7 @@ void phy_detach(struct phy_device *phydev)
>>>  	bus = phydev->mdio.bus;
>>>
>>>  	put_device(&phydev->mdio.dev);
>>> +	module_put(phydev->mdio.dev.driver->owner);
>>>  	module_put(bus->owner);
>>
>> Where is this code called from?
>> You can't call it from the phy driver because the driver can be unloaded
>> as soon as the last reference is removed.
>> At that point the code memory is freed.
> 
> [Mao Wenan] it is called by NIC when it is removed, which aims to disconnect one bound phy driver. If this phy driver
> is not used for this NIC, reference count should be subtracted, and phy driver can be removed if there is no user.
> hns_nic_dev_remove->phy_disconnect->phy_detach
> 
> 
> 
>>
>>>  }
>>>  EXPORT_SYMBOL(phy_detach);
>>> --
>>> 2.7.0
>>>
>>
>>
>> .
>>

@Florian Fainelli, what's your comments about this patch?