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Date: Sat, 22 Jan 2022 00:45:53 +0100 From: Andrew Lunn <andrew@...n.ch> To: Sergei Trofimovich <slyich@...il.com> Cc: netdev@...r.kernel.org Subject: Re: atl1c drivers run 'napi/eth%d-385' named threads with unsubstituted %d On Fri, Jan 21, 2022 at 09:57:47PM +0000, Sergei Trofimovich wrote: > Hia atl1c maintainers! > > This cosmetics bothered me for some time: atl1c driver > shows unexpanded % in kernel thread names. Looks like a > minor bug: > > $ ping -f 172.16.0.1 # host1 > $ top # host2 > ... > 621 root 20 0 0 0 0 S 11.0 0.0 0:05.01 napi/eth%d-385 > 622 root 20 0 0 0 0 S 5.6 0.0 0:02.64 napi/eth%d-386 > ... > > Was happening for a few years. Likely not a recent regression. > > System: > - linux-5.16.1 > - x86_64 > - 02:00.0 Ethernet controller: Qualcomm Atheros AR8151 v2.0 Gigabit Ethernet (rev c0) > > >From what I understand thread name comes from somewhere around: > > net/core/dev.c: > int dev_set_threaded(struct net_device *dev, bool threaded) > ... > err = napi_kthread_create(napi); > ... > static int napi_kthread_create(struct napi_struct *n) > ... > n->thread = kthread_run(napi_threaded_poll, n, "napi/%s-%d", > > drivers/net/ethernet/atheros/atl1c/atl1c_main.c: > static int atl1c_probe(struct pci_dev *pdev, const struct pci_device_id *ent) > ... > dev_set_threaded(netdev, true); > > ${somewhere} (not sure where): > ... > strcpy(netdev->name, "eth%d"); > > I was not able to pinpoint where expansion should ideally happen. > Looks like many driver do `strcpy(netdev->name, "eth%d");` style > initialization and almost none call `dev_set_threaded(netdev, true);`. > > Can you help me find it out how it should be fixed? Hi Sergei This is a fun one. So, the driver does the usual alloc_etherdev_mq() https://elixir.bootlin.com/linux/latest/source/drivers/net/ethernet/atheros/atl1c/atl1c_main.c#L2703 which ends up here: https://elixir.bootlin.com/linux/latest/source/net/ethernet/eth.c#L391 struct net_device *alloc_etherdev_mqs(int sizeof_priv, unsigned int txqs, unsigned int rxqs) { return alloc_netdev_mqs(sizeof_priv, "eth%d", NET_NAME_UNKNOWN, ether_setup, txqs, rxqs); } So at this point in time, the device has the name "eth%d". The normal flow is that sometime later in probe, it calls register_netdev(). https://elixir.bootlin.com/linux/latest/source/net/core/dev.c#L10454 if you follow that down, you get to: __dev_alloc_name(), which does the expansion of the %d to an actual number: https://elixir.bootlin.com/linux/latest/source/net/core/dev.c#L1087 So between alloc_etherdev_mq() and register_netdev(), the device name is not valid. And as you pointed out, dev_set_threaded() tries to use the name, and is called between these two. The atl1c driver appears to be the only driver actually doing this. There is a sysfs interface which can call dev_set_threaded(), but the sysfs interface is probably not available until after register_netdev() has given the interface its name. There is a fix for atl1c. Any time after alloc_etherdev_mq(), the driver can call dev_alloc_name(). So please give this a try. I've not even compile tested it... iff --git a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c index da595242bc13..983a52f77bda 100644 --- a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c +++ b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c @@ -2706,6 +2706,10 @@ static int atl1c_probe(struct pci_dev *pdev, const struct pci_device_id *ent) goto err_alloc_etherdev; } + err = dev_alloc_name(netdev, netdev->name); + if (err < 0) + goto err_init_netdev; + err = atl1c_init_netdev(netdev, pdev); if (err) { dev_err(&pdev->dev, "init netdevice failed\n"); If this works, i can turn it into a real patch submission. Andrew
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