i2c: img-scb: BUG: spinlock bad magic in img_i2c_isr() on early IRQ

[Jaeyoung Chung]

Hi,

img_i2c_probe() in drivers/i2c/busses/i2c-img-scb.c registers the
interrupt handler with devm_request_irq() before it initializes
i2c->lock with spin_lock_init(). If an interrupt arrives before
spin_lock_init() runs, the handler acquires an uninitialized spinlock,
which triggers a kernel warning.

The probe path, in img_i2c_probe():

    i2c = devm_kzalloc(&pdev->dev, ...); /* i2c->lock zeroed */
    ...
    ret = devm_request_irq(&pdev->dev, irq, img_i2c_isr, 0,
                           pdev->name, i2c);                  /* register handler */
    ...
    spin_lock_init(&i2c->lock);                               /* initialize lock */

The interrupt handler, img_i2c_isr(), takes the spinlock.

If the device raises an interrupt before spin_lock_init() runs, the
handler acquires i2c->lock while it is still uninitialized, which
triggers "BUG: spinlock bad magic" when CONFIG_DEBUG_SPINLOCK is
enabled.

Suggested fix: move spin_lock_init(&i2c->lock) above devm_request_irq(),
so the lock is valid before the handler can run.

Reported-by: Sangyun Kim <sangyun.kim@xxxxxxxxx>
Reported-by: Kyungwook Boo <bookyungwook@xxxxxxxxx>

Thanks,
Jaeyoung Chung