linux-kernel - Re: [PATCH 09/30] coresight: cpu-debug: Replace mutex with mutex

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Message-ID: <d9ec6f31-6125-0723-b7d7-5898abeb3289@arm.com>
Date:   Mon, 9 May 2022 17:14:58 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        akpm@...ux-foundation.org, bhe@...hat.com, pmladek@...e.com,
        kexec@...ts.infradead.org
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        bcm-kernel-feedback-list@...adcom.com, coresight@...ts.linaro.org,
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        will@...nel.org, Leo Yan <leo.yan@...aro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Mike Leach <mike.leach@...aro.org>
Subject: Re: [PATCH 09/30] coresight: cpu-debug: Replace mutex with
 mutex_trylock on panic notifier

Hi

On 09/05/2022 14:09, Guilherme G. Piccoli wrote:
> On 28/04/2022 05:11, Suzuki K Poulose wrote:
>> Hi Guilherme,
>>
>> On 27/04/2022 23:49, Guilherme G. Piccoli wrote:
>>> The panic notifier infrastructure executes registered callbacks when
>>> a panic event happens - such callbacks are executed in atomic context,
>>> with interrupts and preemption disabled in the running CPU and all other
>>> CPUs disabled. That said, mutexes in such context are not a good idea.
>>>
>>> This patch replaces a regular mutex with a mutex_trylock safer approach;
>>> given the nature of the mutex used in the driver, it should be pretty
>>> uncommon being unable to acquire such mutex in the panic path, hence
>>> no functional change should be observed (and if it is, that would be
>>> likely a deadlock with the regular mutex).
>>>
>>> Fixes: 2227b7c74634 ("coresight: add support for CPU debug module")
>>> Cc: Leo Yan <leo.yan@...aro.org>
>>> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
>>> Cc: Mike Leach <mike.leach@...aro.org>
>>> Cc: Suzuki K Poulose <suzuki.poulose@....com>
>>> Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
>>
>> How would you like to proceed with queuing this ? I am happy
>> either way. In case you plan to push this as part of this
>> series (I don't see any potential conflicts) :
>>
>> Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>
> 
> Hi Suzuki, some other maintainers are taking the patches to their next
> branches for example. I'm working on V2, and I guess in the end would be
> nice to reduce the size of the series a bit.
> 
> So, do you think you could pick this one for your coresight/next branch
> (or even for rc cycle, your call - this is really a fix)?
> This way, I won't re-submit this one in V2, since it's gonna be merged
> already in your branch.

I have queued this to coresight/next.

Thanks
Suzuki