[PATCH net-next] net: phy: replace mutex_is_locked with lockdep_assert_held in phylib

[PATCH net-next] net: phy: replace mutex_is_locked with lockdep_assert_held in phylib

[Heiner Kallweit]

Switch to lockdep_assert_held(_once), similar to what is being done
in other subsystems. One advantage is that there's zero runtime
overhead if lockdep support isn't enabled.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
 drivers/net/phy/mdio_bus.c   | 4 ++--
 drivers/net/phy/phy.c        | 2 +-
 drivers/net/phy/phy_device.c | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index 2b42e4606..040509b81 100644
--- a/drivers/net/phy/mdio_bus.c
+++ b/drivers/net/phy/mdio_bus.c
@@ -740,7 +740,7 @@ int __mdiobus_read(struct mii_bus *bus, int addr, u32 regnum)
 {
 	int retval;
 
-	WARN_ON_ONCE(!mutex_is_locked(&bus->mdio_lock));
+	lockdep_assert_held_once(&bus->mdio_lock);
 
 	retval = bus->read(bus, addr, regnum);
 
@@ -766,7 +766,7 @@ int __mdiobus_write(struct mii_bus *bus, int addr, u32 regnum, u16 val)
 {
 	int err;
 
-	WARN_ON_ONCE(!mutex_is_locked(&bus->mdio_lock));
+	lockdep_assert_held_once(&bus->mdio_lock);
 
 	err = bus->write(bus, addr, regnum, val);
 
diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
index 45f75533c..9cb7e4dbf 100644
--- a/drivers/net/phy/phy.c
+++ b/drivers/net/phy/phy.c
@@ -724,7 +724,7 @@ static int phy_check_link_status(struct phy_device *phydev)
 {
 	int err;
 
-	WARN_ON(!mutex_is_locked(&phydev->lock));
+	lockdep_assert_held(&phydev->lock);
 
 	/* Keep previous state if loopback is enabled because some PHYs
 	 * report that Link is Down when loopback is enabled.
diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 80c2e646c..8447e56ba 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -1740,7 +1740,7 @@ int __phy_resume(struct phy_device *phydev)
 	struct phy_driver *phydrv = phydev->drv;
 	int ret;
 
-	WARN_ON(!mutex_is_locked(&phydev->lock));
+	lockdep_assert_held(&phydev->lock);
 
 	if (!phydrv || !phydrv->resume)
 		return 0;
-- 
2.30.0

Re: [PATCH net-next] net: phy: replace mutex_is_locked with lockdep_assert_held in phylib

[Andrew Lunn]

On Wed, Jan 06, 2021 at 02:03:40PM +0100, Heiner Kallweit wrote:
> Switch to lockdep_assert_held(_once), similar to what is being done
> in other subsystems. One advantage is that there's zero runtime
> overhead if lockdep support isn't enabled.

Hi Heiner

I'm not sure we are bothered about performance here. MDIO operations
are slow, a mutex check is fast relative to that.

I wonder how many do development work with lockdep enabled? I think i
prefer catching hard to find locking bugs earlier, verses a tiny
performance overhead.

       Andrew

Re: [PATCH net-next] net: phy: replace mutex_is_locked with lockdep_assert_held in phylib

[Heiner Kallweit]

On 06.01.2021 23:39, Andrew Lunn wrote:
> On Wed, Jan 06, 2021 at 02:03:40PM +0100, Heiner Kallweit wrote:
>> Switch to lockdep_assert_held(_once), similar to what is being done
>> in other subsystems. One advantage is that there's zero runtime
>> overhead if lockdep support isn't enabled.
> 
> Hi Heiner
> 
Hi Andrew,

> I'm not sure we are bothered about performance here. MDIO operations
> are slow, a mutex check is fast relative to that.
> 
Right, the performance gain is neglectible here.

What I see is that more and more similar checks (e.g. in_softirq,
in_irq) are migrated to the lockdep framework. And as stated in the
commit message I've seen a number of equivalent patches in other
subsystems.

> I wonder how many do development work with lockdep enabled? I think i
> prefer catching hard to find locking bugs earlier, verses a tiny
> performance overhead.
> 
Well, I always develop with lockdep enabled and like the fact that it
provides a multitude of checks with minimal overhead. Would be
interesting to know the ratio of kernel developers counting on lockdep.

>        Andrew
> 
Heiner

Re: [PATCH net-next] net: phy: replace mutex_is_locked with lockdep_assert_held in phylib

[Andrew Lunn]

On Wed, Jan 06, 2021 at 02:03:40PM +0100, Heiner Kallweit wrote:
> Switch to lockdep_assert_held(_once), similar to what is being done
> in other subsystems. One advantage is that there's zero runtime
> overhead if lockdep support isn't enabled.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew

Re: [PATCH net-next] net: phy: replace mutex_is_locked with lockdep_assert_held in phylib

[Jakub Kicinski]

On Thu, 7 Jan 2021 22:15:06 +0100 Andrew Lunn wrote:
> On Wed, Jan 06, 2021 at 02:03:40PM +0100, Heiner Kallweit wrote:
> > Switch to lockdep_assert_held(_once), similar to what is being done
> > in other subsystems. One advantage is that there's zero runtime
> > overhead if lockdep support isn't enabled.
> > 
> > Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>  
> 
> Reviewed-by: Andrew Lunn <andrew@lunn.ch>

Applied, thanks!

If I was willing to let my pedantic flag fly I'd ask for the lockdep
header to be included explicitly, but I guess in practice the chances
of it not being pulled into sources which use locking is 0.