linux-kernel - Re: [PATCH net v2] net: phy: mscc: fix deadlock in vsc85xx_default

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Message-ID: <20181123150806.GB30913@lunn.ch>
Date:   Fri, 23 Nov 2018 16:08:06 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Quentin Schulz <quentin.schulz@...tlin.com>
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 v2] net: phy: mscc: fix deadlock in
 vsc85xx_default_config

On Fri, Nov 23, 2018 at 09:16:36AM +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 and phy_write and phy_read take and release the lock to write
> or read to a PHY register.
> 
> Let's fix this deadlock by using phy_modify_paged which handles
> correctly a read followed by a write in a non-standard page.
> 
> Fixes: 6a0bfbbe20b0 ("net: phy: mscc: migrate to phy_select/restore_page functions")
> 
> Signed-off-by: Quentin Schulz <quentin.schulz@...tlin.com>
> ---
> 
> v2:
>  - use phy_modify_paged instead of
>  phy_select_page -> __phy_read -> __phy_write -> phy_restore_page
> 
>  drivers/net/phy/mscc.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/phy/mscc.c b/drivers/net/phy/mscc.c
> index 62269e578718..4dcf7ad06259 100644
> --- a/drivers/net/phy/mscc.c
> +++ b/drivers/net/phy/mscc.c
> @@ -810,17 +810,16 @@ static int vsc85xx_default_config(struct phy_device *phydev)
>  
>  	phydev->mdix_ctrl = ETH_TP_MDI_AUTO;
>  	mutex_lock(&phydev->lock);
> -	rc = phy_select_page(phydev, MSCC_PHY_PAGE_EXTENDED_2);
> +
> +	reg_val = RGMII_RX_CLK_DELAY_1_1_NS << RGMII_RX_CLK_DELAY_POS;
> +
> +	rc = phy_modify_paged(phydev, MSCC_PHY_PAGE_EXTENDED_2,
> +			      MSCC_PHY_RGMII_CNTL, RGMII_RX_CLK_DELAY_MASK,
> +			      reg_val);
>  	if (rc < 0)
>  		goto out_unlock;

Hi Quentin

Isn't this goto now pointless. You are not jumping over anything.

      Andrew

>  
> -	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);
> -
>  out_unlock:
> -	rc = phy_restore_page(phydev, rc, rc > 0 ? 0 : rc);
>  	mutex_unlock(&phydev->lock);
>  
>  	return rc;
> -- 
> 2.17.1
>