netdev - Re: [PATCH net-next v2 2/4] net: phy: warn if phy

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Date:   Mon, 21 Jan 2019 19:25:23 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 2/4] net: phy: warn if phy_start is called
 from invalid state

On 21.01.2019 17:40, Andrew Lunn wrote:
> On Sun, Jan 20, 2019 at 10:02:13AM +0100, Heiner Kallweit wrote:
>> phy_start() should be called from states PHY_READY or PHY_HALTED only.
>> Check for this to detect misbehaving drivers. Also the state machine
>> should be started only when being called from one of the valid states.
>>
>> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
>> ---
>>  drivers/net/phy/phy.c | 11 +++++++++--
>>  1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
>> index 3df6aadc5..fd928979b 100644
>> --- a/drivers/net/phy/phy.c
>> +++ b/drivers/net/phy/phy.c
>> @@ -861,9 +861,16 @@ void phy_start(struct phy_device *phydev)
>>  
>>  	mutex_lock(&phydev->lock);
>>  
>> +	if (phydev->state != PHY_READY && phydev->state != PHY_HALTED) {
>> +		WARN(1, "called from state %s\n",
>> +		     phy_state_to_str(phydev->state));
>> +		goto out;
>> +	}
> 
> Hi Heiner
> 
> Warning is good. But jumping to out i'm not so sure about. Drivers
> which are 'broken' work well enough that users don't know they are
> broken. But jumping to out is going to really break them. It seems
> better to have the kernel only warn for one cycle so we find out about
> such drivers and fix them, and later add the goto out.
> 
For all invalid states phy_start() basically was a no-op. All it did was
triggering a state machine run, but for all "running" states the poll
loop was active anyway. And if called from PHY_DOWN, the state machine
does nothing. Therefore I see no scenario where jumping to out would
break anything.

>      Andrew
> 
Heiner