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

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Date: Wed, 11 Oct 2023 00:21:31 +0200
From: Francois Romieu <romieu@...zoreil.com>
To: Marc Kleine-Budde <mkl@...gutronix.de>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Kalle Valo <kvalo@...nel.org>,
        Wei Fang <wei.fang@....com>, kernel@...gutronix.de,
        stable@...r.kernel.org
Subject: Re: [PATCH net] net: davicom: dm9000: dm9000_phy_write(): fix
 deadlock during netdev watchdog handling

Marc Kleine-Budde <mkl@...gutronix.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@...r.kernel.org
> Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.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.

-- 
Ueimor