Re: [PATCH net] net: davicom: dm9000: dm9000_phy_write(): fix deadlock during netdev watchdog handling

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 11.10.2023 00:21:31, Francois Romieu wrote:
> Marc Kleine-Budde <mkl@pengutronix.de> :
> > The dm9000 takes the db->lock spin lock in dm9000_timeout() and calls
> > into dm9000_init_dm9000(). For the DM9000B the PHY is reset with
> > dm9000_phy_write(). That function again takes the db->lock spin lock,
> > which results in a deadlock. For reference the backtrace:
> [...]
> > To workaround similar problem (take mutex inside spin lock ) , a
> > "in_timeout" variable was added in 582379839bbd ("dm9000: avoid
> > sleeping in dm9000_timeout callback"). Use this variable and not take
> > the spin lock inside dm9000_phy_write() if in_timeout is true.
> > 
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
> > ---
> > During the netdev watchdog handling the dm9000 driver takes the same
> > spin lock twice. Avoid this by extending an existing workaround.
> > ---
> 
> I can review it but I can't really endorse it. :o)
> 
> Extending ugly workaround in pre-2000 style device drivers...
> I'd rather see the thing fixed if there is some real use for it.

There definitely are still users of this drivers on modern kernels out
there.

I too don't like the feeling of wrapping more and more duct tape
around existing drivers. How about moving the functionality to
dm9000_phy_write_locked() and leave the locking in dm9000_phy_write().
I will prepare a patch.

regards,
Marc

-- 
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