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spf=none smtp.mailfrom=saiprakash.ranjan@codeaurora.org From: Sai Prakash Ranjan To: Mathieu Poirier , Suzuki K Poulose , Mike Leach Subject: [PATCH] coresight: etm4x: Fix etm4_count race using atomic variable Date: Mon, 27 Jul 2020 11:37:28 +0530 Message-Id: <20200727060728.15027-1-saiprakash.ranjan@codeaurora.org> X-Mailer: git-send-email 2.27.0 MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200727_020846_936536_78793EBF X-CRM114-Status: GOOD ( 15.50 ) X-Spam-Score: 0.0 (/) X-Spam-Report: SpamAssassin version 3.4.4 on merlin.infradead.org summary: Content analysis details: (0.0 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at https://www.dnswl.org/, no trust [69.72.43.7 listed in list.dnswl.org] 0.0 RCVD_IN_MSPIKE_H3 RBL: Good reputation (+3) [69.72.43.7 listed in wl.mailspike.net] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid 0.0 RCVD_IN_MSPIKE_WL Mailspike good senders X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Sai Prakash Ranjan , linux-arm-msm@vger.kernel.org, coresight@lists.linaro.org, linux-kernel@vger.kernel.org, Stephen Boyd , linux-arm-kernel@lists.infradead.org Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org 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; ret = cpu_pm_register_notifier(&etm4_cpu_pm_nb); @@ -1434,13 +1434,13 @@ static int etm4_pm_setup_cpuslocked(void) cpu_pm_unregister_notifier(&etm4_cpu_pm_nb); reduce_count: - --etm4_count; + atomic_dec(&etm4_count); return ret; } static void etm4_pm_clear(void) { - if (--etm4_count != 0) + if (atomic_dec_return(&etm4_count) != 0) return; cpu_pm_unregister_notifier(&etm4_cpu_pm_nb);