linux-kernel - Re: [PATCH 4/5] ath10k: detect conf_mutex held ath10k_drain

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Message-ID: <87lfbwtjls.fsf@codeaurora.org>
Date:   Wed, 10 Feb 2021 10:25:35 +0200
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Shuah Khan <skhan@...uxfoundation.org>
Cc:     davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
        ath10k@...ts.infradead.org
Subject: Re: [PATCH 4/5] ath10k: detect conf_mutex held ath10k_drain_tx() calls

Shuah Khan <skhan@...uxfoundation.org> writes:

> ath10k_drain_tx() must not be called with conf_mutex held as workers can
> use that also. Add check to detect conf_mutex held calls.
>
> Signed-off-by: Shuah Khan <skhan@...uxfoundation.org>

The commit log does not answer to "Why?". How did you find this? What
actual problem are you trying to solve?

> ---
>  drivers/net/wireless/ath/ath10k/mac.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/net/wireless/ath/ath10k/mac.c b/drivers/net/wireless/ath/ath10k/mac.c
> index 53f92945006f..3545ce7dce0a 100644
> --- a/drivers/net/wireless/ath/ath10k/mac.c
> +++ b/drivers/net/wireless/ath/ath10k/mac.c
> @@ -4566,6 +4566,7 @@ static void ath10k_mac_op_wake_tx_queue(struct ieee80211_hw *hw,
>  /* Must not be called with conf_mutex held as workers can use that also. */
>  void ath10k_drain_tx(struct ath10k *ar)
>  {
> +	WARN_ON(lockdep_is_held(&ar->conf_mutex));

Empty line after WARN_ON().

Shouldn't this check debug_locks similarly lockdep_assert_held() does?

#define lockdep_assert_held(l)	do {				\
		WARN_ON(debug_locks && !lockdep_is_held(l));	\
	} while (0)

And I suspect you need #ifdef CONFIG_LOCKDEP which should fix the kbuild
bot error.

But honestly I would prefer to have lockdep_assert_not_held() in
include/linux/lockdep.h, much cleaner that way. Also
i915_gem_object_lookup_rcu() could then use the same macro.

-- 
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https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches