Re: [PATCH net] net: dsa: microchip: initialize the IRQ access mutex

[Daniel Machon]

> ksz_switch_register() initializes dev_mutex, regmap_mutex, alu_mutex and
> vlan_mutex but not lock_irq, which the IRQ chip takes in its bus lock
> callbacks on every mask and unmask of a switch interrupt, and the PTP
> code takes the same way. The zeroed mutex happens to work on the
> uncontended fast path, but with CONFIG_DEBUG_MUTEXES the first lock,
> from the IRQ domain mapping during probe, warns:
> 
>   DEBUG_LOCKS_WARN_ON(lock->magic != lock)
>   WARNING: kernel/locking/mutex.c:625 at __mutex_lock
>   ...
>   ksz_irq_domain_map
>   irq_domain_associate_locked
>   irq_create_mapping_affinity
>   ksz_irq_common_setup
>   ksz9477_setup
>   dsa_register_switch
>   ksz_spi_probe
> 
> and turns lock debugging off for the rest of the boot.
> 
> Initialize it with the other mutexes.
> 
> Triggered at every boot of a KSZ9897S over SPI on an i.MX6 SoloX board
> with CONFIG_DEBUG_MUTEXES, on v7.4-rc1 and earlier. With this patch the
> same board boots with lock debugging enabled and it stays enabled
> (debug_locks 1) through two hours of unrelated stress tests.
> 
> Fixes: c9cd961c0d43 ("net: dsa: microchip: lan937x: add interrupt support for port phy link")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Tapio Reijonen <tapio.reijonen@xxxxxxxxxxx>

Reviewed-by: Daniel Machon <daniel.machon@xxxxxxxxxxxxx>