linux-kernel - Re: [PATCH net] net: phy: mscc: fix deadlock in vsc85xx_default

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Message-ID: <20181123081816.vgtsx6fxdsrjjiza@qschulz>
Date:   Fri, 23 Nov 2018 09:18:16 +0100
From:   Quentin Schulz <quentin.schulz@...tlin.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     davem@...emloft.net, f.fainelli@...il.com,
        allan.nielsen@...rochip.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, thomas.petazzoni@...tlin.com,
        alexandre.belloni@...tlin.com
Subject: Re: [PATCH net] net: phy: mscc: fix deadlock in
 vsc85xx_default_config

Hi Andrew,

On Thu, Nov 22, 2018 at 08:28:37PM +0100, Andrew Lunn wrote:
> On Thu, Nov 22, 2018 at 02:12:32PM +0100, Quentin Schulz wrote:
> > The vsc85xx_default_config function called in the vsc85xx_config_init
> > function which is used by VSC8530, VSC8531, VSC8540 and VSC8541 PHYs
> > mistakenly calls phy_read and phy_write in-between phy_select_page and
> > phy_restore_page.
> > 
> > phy_select_page and phy_restore_page actually take and release the MDIO
> > bus lock so __phy_write and __phy_read (which assume that you already
> > have the MDIO bus lock unlike phy_write and phy_read) should be used for
> > any call in between the two said functions.
> > 
> > Let's fix this deadlock.
> > 
> > Fixes: 6a0bfbbe20b0 ("net: phy: mscc: migrate to phy_select/restore_page functions")
> > 
> > Signed-off-by: Quentin Schulz <quentin.schulz@...tlin.com>
> > ---
> >  drivers/net/phy/mscc.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/phy/mscc.c b/drivers/net/phy/mscc.c
> > index 62269e578718..6856fe4d1a60 100644
> > --- a/drivers/net/phy/mscc.c
> > +++ b/drivers/net/phy/mscc.c
> > @@ -814,10 +814,10 @@ static int vsc85xx_default_config(struct phy_device *phydev)
> >  	if (rc < 0)
> >  		goto out_unlock;
> >  
> > -	reg_val = phy_read(phydev, MSCC_PHY_RGMII_CNTL);
> > +	reg_val = __phy_read(phydev, MSCC_PHY_RGMII_CNTL);
> >  	reg_val &= ~(RGMII_RX_CLK_DELAY_MASK);
> >  	reg_val |= (RGMII_RX_CLK_DELAY_1_1_NS << RGMII_RX_CLK_DELAY_POS);
> > -	phy_write(phydev, MSCC_PHY_RGMII_CNTL, reg_val);
> > +	__phy_write(phydev, MSCC_PHY_RGMII_CNTL, reg_val);
> 
> Hi Quentin
> 
> You appear to be only accessing a single register, read/modify/write.
> I think you can use phy_modify_paged(), which will take care of all
> the locking for you.
> 

Grmbl... Of course :)

Thanks,
Quentin

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