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Date: Mon, 12 Dec 2016 08:33:24 -0800 From: Florian Fainelli <f.fainelli@...il.com> To: maowenan <maowenan@...wei.com>, David Laight <David.Laight@...LAB.COM>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "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 12/12/2016 12:49 AM, maowenan wrote: > > > 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? I am trying to reproduce what you are seeing, but at first glance is looks like an appropriate solution to me. Do you mind giving me a couple more days? Thanks! -- Florian
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