linux-kernel - Re: [PATCH net] net: phy: Fix deadlocking in phy

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Message-ID: <6e52f88e-73ad-4e2a-90ca-ada471f30b9d@lunn.ch>
Date:   Fri, 18 Aug 2023 15:07:49 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Francesco Dolcini <francesco.dolcini@...adex.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: phy: Fix deadlocking in phy_error() invocation

On Fri, Aug 18, 2023 at 03:54:45PM +0300, Serge Semin wrote:
>  static void phy_process_error(struct phy_device *phydev)
>  {
> -	mutex_lock(&phydev->lock);
> +	/* phydev->lock must be held for the state change to be safe */
> +	if (!mutex_is_locked(&phydev->lock))
> +		phydev_err(phydev, "PHY-device data unsafe context\n");
> +
>  	phydev->state = PHY_ERROR;
> -	mutex_unlock(&phydev->lock);
>  
>  	phy_trigger_machine(phydev);
>  }

Thanks for the patch Serge. It looks like a good implementation of
what i suggested. But thinking about it further, if the error ever
appears in somebodies kernel log, there is probably not enough
information to actually fix it. There is no call path. So i think it
should actually use WARN_ON_ONCE() so we get a stack trace.

Sorry for changing my mind.

    Andrew

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