netdev - Re: [PATCH] cdc_ncm: do not call usbnet_link_change from cdc_ncm

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Date:	Tue, 8 Mar 2016 11:43:26 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Bjørn Mork <bjorn@...k.no>
Cc:	David Miller <davem@...emloft.net>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Oliver Neukum <oneukum@...e.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	USB list <linux-usb@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH] cdc_ncm: do not call usbnet_link_change from cdc_ncm_bind

On Mon, Mar 7, 2016 at 12:15 PM, Bjørn Mork <bjorn@...k.no> wrote:
> usbnet_link_change will call schedule_work and should be
> avoided if bind is failing. Otherwise we will end up with
> scheduled work referring to a netdev which has gone away.
>
> Instead of making the call conditional, we can just defer
> it to usbnet_probe, using the driver_info flag made for
> this purpose.

So looking at this, I wonder...

Why is that FLAG_LINK_INTR thing not just always used?

The _only_ thing that FLAG_LINK_INTR does is to cause

        usbnet_link_change(dev, 0, 0);

to be called after network device attach. That doesn't seem to be controversial.

Looking at some examples, we have ax88179_178a.c that doesn't set the
flag, but instead does that usbnet_link_change() call at the end of
ax88179_bind().

There are a few drivers that seem to never call that
usbnet_link_change() at all, and don't have that FLAG_LINK_INTR flag.
Would they break?

Stupid grep:

    git grep -lw FLAG_ETHER |
        xargs grep -L FLAG_LINK_INTR |
        xargs grep -L usbnet_link_change |
        sed 's:drivers/net/usb/::'

gives

    cdc_eem.c
    ch9200.c
    cx82310_eth.c
    int51x1.c
    rndis_host.c

so maybe that FLAG_LINK_INTR si required.

Why is it called "FLAG_LINK_INTR" anyway? There doesn't seem to be
anything "INTR" about it.

               Linus