On Fri, May 26, 2023 at 03:35:37PM +0800, Chen-Yu Tsai wrote:
> 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@xxxxxxxxxxxx>
Good catch, thank you!
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> ---
>
> Also, the original patch subject said "srcu_update", however the data
> structure ended up as "srcu_usage". Maybe that could be updated?
>
> include/linux/notifier.h | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/include/linux/notifier.h b/include/linux/notifier.h
> index 2aba75145144..86544707236a 100644
> --- a/include/linux/notifier.h
> +++ b/include/linux/notifier.h
> @@ -106,12 +106,22 @@ extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
> #define RAW_NOTIFIER_INIT(name) { \
> .head = NULL }
>
> +#ifdef CONFIG_TREE_SRCU
> #define SRCU_NOTIFIER_INIT(name, pcpu) \
> { \
> .mutex = __MUTEX_INITIALIZER(name.mutex), \
> .head = NULL, \
> + .srcuu = __SRCU_USAGE_INIT(name.srcuu), \
> .srcu = __SRCU_STRUCT_INIT(name.srcu, name.srcuu, pcpu), \
> }
> +#else
> +#define SRCU_NOTIFIER_INIT(name, pcpu) \
> + { \
> + .mutex = __MUTEX_INITIALIZER(name.mutex), \
> + .head = NULL, \
> + .srcu = __SRCU_STRUCT_INIT(name.srcu, name.srcuu, pcpu), \
> + }
> +#endif
>
> #define ATOMIC_NOTIFIER_HEAD(name) \
> struct atomic_notifier_head name = \
> --
> 2.41.0.rc0.172.g3f132b7071-goog
>
