[PATCH] notifier: Initialize new struct srcu_usage field

[AngeloGioacchino Del Regno]

Il 26/05/23 09:35, Chen-Yu Tsai ha scritto:
> In commit 95433f726301 ("srcu: Begin offloading srcu_struct fields to
> srcu_update"), a new struct srcu_usage field was added, but was not
> properly initialized. This led to a "spinlock bad magic" BUG when
> the SRCU notifier was ever used. This was observed in the MediaTek
> CCI devfreq driver on next-20230525. Trimmed stack trace as follows:
> 
>      BUG: spinlock bad magic on CPU#4, swapper/0/1
>       lock: 0xffffff80ff529ac0, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
>      Call trace:
>       spin_bug+0xa4/0xe8
>       do_raw_spin_lock+0xec/0x120
>       _raw_spin_lock_irqsave+0x78/0xb8
>       synchronize_srcu+0x3c/0x168
>       srcu_notifier_chain_unregister+0x5c/0xa0
>       cpufreq_unregister_notifier+0x94/0xe0
>       devfreq_passive_event_handler+0x7c/0x3e0
>       devfreq_remove_device+0x48/0xe8
> 
> Add __SRCU_USAGE_INIT() to SRCU_NOTIFIER_INIT() so that srcu_usage gets
> initialized properly.
> 
> Fixes: 95433f726301 ("srcu: Begin offloading srcu_struct fields to srcu_update")
> Signed-off-by: Chen-Yu Tsai <wenst at chromium.org>

Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>