[PATCH net] net: phy: mscc: fix deadlock in vsc85xx_default_config

[PATCH net] net: phy: mscc: fix deadlock in vsc85xx_default_config

[Quentin Schulz]

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@bootlin.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);
 
 out_unlock:
 	rc = phy_restore_page(phydev, rc, rc > 0 ? 0 : rc);
-- 
2.17.1

Re: [PATCH net] net: phy: mscc: fix deadlock in vsc85xx_default_config

[Andrew Lunn]

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@bootlin.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.

    Andrew

Re: [PATCH net] net: phy: mscc: fix deadlock in vsc85xx_default_config

[Quentin Schulz]

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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@bootlin.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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