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

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

[Tapio Reijonen]

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@vger.kernel.org
Signed-off-by: Tapio Reijonen <tapio.reijonen@vaisala.com>
---
Claude Code (Anthropic) located the missing initialization from the
warning's stack and drafted the commit message; I reviewed the code path
and the Fixes target, and ran the boots with and without the patch.
---
 drivers/net/dsa/microchip/ksz_common.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
index 767c8fe8e819a5c2b76d73d1537e1457b4408582..00ddb692ede013c41a0fe515570d023e35182b52 100644
--- a/drivers/net/dsa/microchip/ksz_common.c
+++ b/drivers/net/dsa/microchip/ksz_common.c
@@ -4023,6 +4023,7 @@ int ksz_switch_register(struct ksz_device *dev)
 	mutex_init(&dev->regmap_mutex);
 	mutex_init(&dev->alu_mutex);
 	mutex_init(&dev->vlan_mutex);
+	mutex_init(&dev->lock_irq);
 
 	ret = ksz_switch_detect(dev);
 	if (ret)

---
base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4
change-id: 20261103-ksz-irq-mutex-init-ef8f8677db06

Best regards,
-- 
Tapio Reijonen <tapio.reijonen@vaisala.com>

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@vger.kernel.org
> Signed-off-by: Tapio Reijonen <tapio.reijonen@vaisala.com>

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

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

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Wed, 04 Nov 2026 07:58:35 +0000 you wrote:
> 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:
> 
> [...]

Here is the summary with links:
  - [net] net: dsa: microchip: initialize the IRQ access mutex
    https://git.kernel.org/netdev/net/c/ba1dc196502f

You are awesome, thank you!
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