netdev - Re: atl1c drivers run 'napi/eth%d-385' named threads with unsubstituted %d

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Date:   Sat, 22 Jan 2022 22:01:21 +0000
From:   Sergei Trofimovich <slyich@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        netdev@...r.kernel.org
Subject: Re: atl1c drivers run 'napi/eth%d-385' named threads with
 unsubstituted %d

On Sat, 22 Jan 2022 20:40:51 +0100
Andrew Lunn <andrew@...n.ch> wrote:

> > > Oh, yes. I looked at some of the users. And some do take rtnl before
> > > calling it. And some don't!
> > > 
> > > Looking at register_netdev(), it seems we need something like:
> > > 
> > > 	if (rtnl_lock_killable()) {
> > > 	       err = -EINTR;
> > > 	       goto err_init_netdev;
> > > 	}
> > > 	err = dev_alloc_name(netdev, netdev->name);
> > > 	rtnl_unlock();
> > > 	if (err < 0)
> > > 		goto err_init_netdev;
> > > 
> > > 
> > > It might also be a good idea to put a ASSERT_RTNL() in
> > > __dev_alloc_name() to catch any driver doing this wrong.  
> 
> I looked at it some more, and some of the current users. And this does
> not really work. There is a race condition.
> 
> Taking rtnl means you at least get a valid name, while you hold
> rtnl. But it does not keep track of the name it just gave out. As a
> result, you can release rtnl, and another device can jump in and be
> given the same name in register_netdev(). When this driver then calls
> register_netdev() the core will notice the clash and return -EEXISTS,
> causing the probe to fail.
> 
> There are some drivers which take rtnl and keep it until after calling
> register_netdevice(), rather than register_netdev(), but this is
> rather ugly. And there are some drivers which don't take the lock, and
> just hope they don't hit the race.
> 
> Maybe a better fix for this driver is:
> 
> From a5fc0e127bdc4b6ba4fb923012729cbf3d529996 Mon Sep 17 00:00:00 2001
> From: Andrew Lunn <andrew@...n.ch>
> Date: Sat, 22 Jan 2022 13:33:58 -0600
> Subject: [PATCH] net: ethernet: atl1c: Move dev_set_threaded() after
>  register_netdev()
> 
> dev_set_threaded() creates new kernel threads to perform napi. The
> threads are given a name based on the interface name. However, the
> interface is not allocated a name until register_netdev() is called.
> By moving the call to dev_set_threaded() to later in the probe
> function, odd thread names like napi/eth%d-385 are avoided.
> 
> Signed-off-by: Andrew Lunn <andrew@...n.ch>

This patch also works:

    687 root 20 0 0 0 0 R 6.7   0.0 0:00.15 napi/eth0-386
    688 root 20 0 0 0 0 S 6.7   0.0 0:00.32 napi/eth0-385

tested in the same environment on top of 5.16.1:

Tested-by: Sergei Trofimovich <slyich@...il.com>

Thank you!

> ---
>  drivers/net/ethernet/atheros/atl1c/atl1c_main.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> index da595242bc13..9b8088905946 100644
> --- a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> +++ b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> @@ -2728,7 +2728,7 @@ static int atl1c_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>         adapter->mii.mdio_write = atl1c_mdio_write;
>         adapter->mii.phy_id_mask = 0x1f;
>         adapter->mii.reg_num_mask = MDIO_CTRL_REG_MASK;
> -       dev_set_threaded(netdev, true);
> +
>         for (i = 0; i < adapter->rx_queue_count; ++i)
>                 netif_napi_add(netdev, &adapter->rrd_ring[i].napi,
>                                atl1c_clean_rx, 64);
> @@ -2781,6 +2781,8 @@ static int atl1c_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>                 goto err_register;
>         }
>  
> +       dev_set_threaded(netdev, true);
> +
>         cards_found++;
>         return 0;
>  
> -- 
> 2.34.1


-- 

  Sergei