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

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Message-ID: <65f24bc5-2211-0139-ee12-b2608e81ceb1@igalia.com>
Date:   Mon, 9 May 2022 10:09:21 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        akpm@...ux-foundation.org, bhe@...hat.com, pmladek@...e.com,
        kexec@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com, coresight@...ts.linaro.org,
        linuxppc-dev@...ts.ozlabs.org, linux-alpha@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-edac@...r.kernel.org,
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        tglx@...utronix.de, vgoyal@...hat.com, vkuznets@...hat.com,
        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

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.

Thanks in advance,


Guilherme