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Date:   Thu, 10 Dec 2020 10:27:31 +0800
From:   Wen Gong <wgong@codeaurora.org>
To:     Kalle Valo <kvalo@codeaurora.org>
Cc:     linux-wireless@vger.kernel.org, ath10k@lists.infradead.org
Subject: Re: [PATCH v3] ath10k: add flag to protect napi operation to avoid
 dead loop hang
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On 2020-12-09 17:24, Kalle Valo wrote:
> Wen Gong <wgong@codeaurora.org> writes:
> 
>> On 2020-09-08 00:22, Kalle Valo wrote:
>> 
>>> Just like with the recent firmware restart patch, isn't
>>> ar->napi_enabled
>>> racy? Wouldn't test_and_set_bit() and test_and_clear_bit() be safer?
>>> 
>>> Or are we holding a lock? But then that should be documented with
>>> lockdep_assert_held().
>> 
>> yes, ath10k_hif_start is only called from ath10k_core_start, it has
>> "lockdep_assert_held(&ar->conf_mutex)", and ath10k_hif_stop is only
>> called from ath10k_core_stop, it also has
>> "lockdep_assert_held(&ar->conf_mutex)". then it will not 2 thread both
>> enter ath10k_hif_start/ath10k_hif_stop meanwhile.
> 
> Ok, but every function depending on a lock being held should still call
> lockdep_assert_held(), that way we can catch the bug if locking changes
> later. So it's not enough that ath10k_core_stop() has
> lockdep_assert_held(), also these napi functions should have it.
> 
> I actually decided to switch using ATH10K_FLAG_NAPI_ENABLED with
> set_bit() & co, simpler locking that way and no lockdep_assert_held()
> needed anymore. Please check my changes in the pending branch, I have
> only compile tested them:
I checked, it only changed ar->napi_enabled to flag 
ATH10K_FLAG_NAPI_ENABLED,
not found probelm.
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git/commit/?h=pending&id=e0a466d296bd862080f7796b41349f9f586272c9