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In-Reply-To: <20200729051310.18436-1-saiprakash.ranjan@codeaurora.org>
References: <20200729051310.18436-1-saiprakash.ranjan@codeaurora.org>
Subject: Re: [PATCHv3] coresight: etm4x: Fix etm4_count race by moving cpuhp callbacks to init
From:   Stephen Boyd <swboyd@chromium.org>
Cc:     coresight@lists.linaro.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
To:     Mathieu Poirier <mathieu.poirier@linaro.org>,
        Mike Leach <mike.leach@linaro.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
        Suzuki K Poulose <suzuki.poulose@arm.com>
Date:   Mon, 03 Aug 2020 13:36:04 -0700
Message-ID: <159648696483.1360974.2828241668912900602@swboyd.mtv.corp.google.com>
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Quoting Sai Prakash Ranjan (2020-07-28 22:13:10)
> etm4_count keeps track of number of ETMv4 registered and on some systems,
> a race is observed on etm4_count variable which can lead to multiple calls
> to cpuhp_setup_state_nocalls_cpuslocked(). This function internally calls
> cpuhp_store_callbacks() which prevents multiple registrations of callbacks
> for a given state and due to this race, it returns -EBUSY leading to ETM
> probe failures like below.
>=20
>  coresight-etm4x: probe of 7040000.etm failed with error -16
>=20
> This race can easily be triggered with async probe by setting probe type
> as PROBE_PREFER_ASYNCHRONOUS and with ETM power management property
> "arm,coresight-loses-context-with-cpu".
>=20
> Prevent this race by moving cpuhp callbacks to etm driver init since the
> cpuhp callbacks doesn't have to depend on the etm4_count and can be once
> setup during driver init. Similarly we move cpu_pm notifier registration
> to driver init and completely remove etm4_count usage. Also now we can
> use non cpuslocked version of cpuhp callbacks with this movement.
>=20
> Fixes: 9b6a3f3633a5 ("coresight: etmv4: Fix CPU power management setup in=
 probe() function")
> Fixes: 58eb457be028 ("hwtracing/coresight-etm4x: Convert to hotplug state=
 machine")
> Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
> ---

Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Tested-by: Stephen Boyd <swboyd@chromium.org>