linux-kernel - Re: [PATCH v2 0/2] wifi: ath11k: fix event locking

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Message-ID: <ZTfgJCBxsNv3bVjv@hovoldconsulting.com>
Date:   Tue, 24 Oct 2023 17:17:56 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Kalle Valo <kvalo@...nel.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Jeff Johnson <quic_jjohnson@...cinc.com>,
        ath11k@...ts.infradead.org, linux-wireless@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] wifi: ath11k: fix event locking

On Tue, Oct 24, 2023 at 05:07:38PM +0300, Kalle Valo wrote:
> Johan Hovold <johan+linaro@...nel.org> 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());

Johan