ath11k: checking RCU usage

[Kalle Valo]

(old discussion, changing title)

Johan Hovold <johan@xxxxxxxxxx> writes:

> On Tue, Oct 24, 2023 at 05:07:38PM +0300, Kalle Valo wrote:
>
>> Johan Hovold <johan+linaro@xxxxxxxxxx> writes:
>> 
>> > RCU lockdep reported suspicious RCU usage when accessing the temperature
>> > sensor. Inspection revealed that the DFS radar event code was also
>> > missing the required RCU read-side critical section marking.
>> >
>> > Johan
>> >
>> >
>> > Changes in v2
>> >  - add the missing rcu_read_unlock() to an
>> >    ath11k_wmi_pdev_temperature_event() error path as noticed by Jeff
>> >
>> >
>> > Johan Hovold (2):
>> >   wifi: ath11k: fix temperature event locking
>> >   wifi: ath11k: fix dfs radar event locking
>> 
>> Thanks for the fixes. I really like using lockdep_assert_held() to
>> document if a function requires some lock held, is there anything
>> similar for RCU?
>
> Not really, but the checking is instead built into the primitives like
> rcu_dereference() and enabled whenever CONFIG_PROVE_RCU is set.
>
> For some special cases, we have open-coded checks like:
>
> 	RCU_LOCKDEP_WARN(!rcu_read_lock_held());
>
> which similarly depend on CONFIG_PROVE_RCU or simply
>
> 	WARN_ON_ONCE(!rcu_read_lock_held());

I just found out that sparse has __must_hold():

https://lore.kernel.org/linux-wireless/87sf31hhfp.fsf@xxxxxxxxxx/

That looks promising, should we start using that in ath11k and ath12k to
check our RCU usage?

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