linux-kernel - Re: [PATCH 1/8] coresight: Fix issue where a source device's helpers aren't disabled

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Message-ID: <3c7665ff-b2e2-f10d-a78a-4ddc1791926f@arm.com>
Date:   Wed, 13 Dec 2023 13:54:26 +0000
From:   James Clark <james.clark@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        coresight@...ts.linaro.org
Cc:     Mike Leach <mike.leach@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH 1/8] coresight: Fix issue where a source device's helpers
 aren't disabled



On 12/12/2023 17:44, Suzuki K Poulose wrote:
> Hi James
> 
> On 12/12/2023 15:53, James Clark wrote:
>> The linked commit reverts the change that accidentally used some sysfs
>> enable/disable functions from Perf which broke the refcounting, but it
>> also removes the fact that the sysfs disable function disabled the
>> helpers.
> 
> 
>>
>> Add a new wrapper function that does both which is used by both Perf and
>> sysfs, and label the sysfs disable function appropriately. The naming of
>> all of the functions will be tidied up later to avoid this happening
>> again.
>>
>> Fixes: 287e82cf69aa ("coresight: Fix crash when Perf and sysfs modes
>> are used concurrently")
> 
> But we still don't "enable" the helpers from perf mode with this patch.
> i.e., we use source_ops()->enable directly. So, I guess this patch
> doesn't fix a bug as such. But that said, it would be good to
> enable/disable helpers for sources, in perf mode.
> 
> Suzuki

We do, it happens in coresight_enable_path() which Perf uses. I added
the comment below about that.

 [...]

>>   +/*
>> + * Helper function to call source_ops(csdev)->disable and also
>> disable the
>> + * helpers.
>> + *
>> + * There is an imbalance between coresight_enable_path() and
>> + * coresight_disable_path(). Enabling also enables the source's
>> helpers as part
>> + * of the path, but disabling always skips the first item in the path
>> (which is
>> + * the source), so sources and their helpers don't get disabled as
>> part of that
>> + * function and we need the extra step here.
>> + */

The reason coresight_disable_path() skips the first item is because it's
used after errors where a path is only partially enabled and it unwinds,
skipping the last item, because the last item didn't enable.

It seemed a bit more intrusive to change that, and it's already working.