From: Wen Gong <wgong@codeaurora.org>
To: Ben Greear <greearb@candelatech.com>
Cc: Kalle Valo <kvalo@codeaurora.org>,
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
Date: Thu, 10 Dec 2020 10:29:35 +0800 [thread overview]
Message-ID: <e4b4f4d1fadd4d691729ef422e8732d7@codeaurora.org> (raw)
In-Reply-To: <8a97f5ba-8eba-d61b-4c92-bdfd08d388ee@candelatech.com>
On 2020-12-09 23:00, Ben Greear wrote:
> On 12/9/20 1:24 AM, 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:
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git/commit/?h=pending&id=e0a466d296bd862080f7796b41349f9f586272c9
>>
>
> Why do you not need locking? You can't just check a bit is set and
> then do work and set
> it later without locking, two concurrent CPU threads can pass the
> first check and both get into
> the logic below it?
>
maybe because which I said before:
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.
> Thanks,
> Ben
next prev parent reply other threads:[~2020-12-10 2:30 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-28 12:22 [PATCH v3] ath10k: add flag to protect napi operation to avoid dead loop hang Wen Gong
2020-08-28 14:09 ` Krishna Chaitanya
2020-12-09 9:11 ` Kalle Valo
2020-09-07 16:23 ` Kalle Valo
[not found] ` <87d02x1rqb.fsf@codeaurora.org>
2020-09-08 3:45 ` Wen Gong
[not found] ` <010101746bd17881-819242de-7cbb-4df3-93e2-59473d281155-000000@us-west-2.amazonses.com>
2020-12-09 9:24 ` Kalle Valo
2020-12-09 15:00 ` Ben Greear
2020-12-10 2:29 ` Wen Gong [this message]
2020-12-15 8:05 ` Kalle Valo
2020-12-15 7:56 ` Kalle Valo
2020-12-10 2:27 ` Wen Gong
2020-12-17 6:52 ` Kalle Valo
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