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Mon, 27 Jul 2020 08:56:01 GMT Received: by smtp.codeaurora.org (Postfix, from userid 1001) id A3CEFC43395; Mon, 27 Jul 2020 08:56:01 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: saiprakash.ranjan) by smtp.codeaurora.org (Postfix) with ESMTPSA id 0AEF0C433C9; Mon, 27 Jul 2020 08:56:01 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Mon, 27 Jul 2020 14:26:00 +0530 From: Sai Prakash Ranjan To: Mathieu Poirier , Suzuki K Poulose , Mike Leach Cc: linux-arm-kernel@lists.infradead.org, linux-arm-msm@vger.kernel.org, Stephen Boyd , linux-kernel@vger.kernel.org, coresight@lists.linaro.org Subject: Re: [PATCH] coresight: etm4x: Fix etm4_count race using atomic variable In-Reply-To: <20200727060728.15027-1-saiprakash.ranjan@codeaurora.org> References: <20200727060728.15027-1-saiprakash.ranjan@codeaurora.org> Message-ID: <0541ded117bb2a63481de8c015282b11@codeaurora.org> X-Sender: saiprakash.ranjan@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-07-27 11:37, Sai Prakash Ranjan wrote: > 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. > > coresight-etm4x: probe of 7040000.etm failed with error -16 > > 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". > > Prevent this race by converting etm4_count variable to atomic. > > Fixes: 9b6a3f3633a5 ("coresight: etmv4: Fix CPU power management setup > in probe() function") > Fixes: 58eb457be028 ("hwtracing/coresight-etm4x: Convert to hotplug > state machine") > Suggested-by: Mike Leach > (Mike: Rootcause and context for commit message) > Signed-off-by: Sai Prakash Ranjan > --- > drivers/hwtracing/coresight/coresight-etm4x.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c > b/drivers/hwtracing/coresight/coresight-etm4x.c > index 6d7d2169bfb2..f256ea744c51 100644 > --- a/drivers/hwtracing/coresight/coresight-etm4x.c > +++ b/drivers/hwtracing/coresight/coresight-etm4x.c > @@ -49,7 +49,7 @@ MODULE_PARM_DESC(pm_save_enable, > "Save/restore state on power down: 1 = never, 2 = self-hosted"); > > /* The number of ETMv4 currently registered */ > -static int etm4_count; > +static atomic_t etm4_count; > static struct etmv4_drvdata *etmdrvdata[NR_CPUS]; > static void etm4_set_default_config(struct etmv4_config *config); > static int etm4_set_event_filters(struct etmv4_drvdata *drvdata, > @@ -1403,7 +1403,7 @@ static int etm4_pm_setup_cpuslocked(void) > { > int ret; > > - if (etm4_count++) > + if (atomic_inc_return(&etm4_count)) > return 0; > Sorry, I messed up here, will send a next version fixing this. Thanks, Sai -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation