[PATCH v7 03/11] coresight: etm3x: Always set tracer's device mode on target CPU

[Leo Yan]

The ETMv3 driver shares the same issue as ETMv4 regarding race
conditions when accessing the device mode.

This commit applies the same fix: ensuring that the device mode is
modified only by the target CPU to eliminate race conditions across
CPUs.

Fixes: 22fd532eaa0c ("coresight: etm3x: adding operation mode for etm_enable()")
Reviewed-by: Mike Leach <mike.leach at linaro.org>
Tested-by: James Clark <james.clark at linaro.org>
Signed-off-by: Leo Yan <leo.yan at arm.com>
---
 drivers/hwtracing/coresight/coresight-etm3x-core.c | 59 +++++++++++++++-------
 1 file changed, 40 insertions(+), 19 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm3x-core.c b/drivers/hwtracing/coresight/coresight-etm3x-core.c
index 45630a1cd32fbd05ec8b2a6979f0174cacce365e..a5e809589d3e382acde24ee457e94e5dcb18ea35 100644
--- a/drivers/hwtracing/coresight/coresight-etm3x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm3x-core.c
@@ -439,13 +439,26 @@ struct etm_enable_arg {
 	int rc;
 };
 
-static void etm_enable_hw_smp_call(void *info)
+static void etm_enable_sysfs_smp_call(void *info)
 {
 	struct etm_enable_arg *arg = info;
+	struct coresight_device *csdev;
 
 	if (WARN_ON(!arg))
 		return;
+
+	csdev = arg->drvdata->csdev;
+	if (!coresight_take_mode(csdev, CS_MODE_SYSFS)) {
+		/* Someone is already using the tracer */
+		arg->rc = -EBUSY;
+		return;
+	}
+
 	arg->rc = etm_enable_hw(arg->drvdata);
+
+	/* The tracer didn't start */
+	if (arg->rc)
+		coresight_set_mode(csdev, CS_MODE_DISABLED);
 }
 
 static int etm_cpu_id(struct coresight_device *csdev)
@@ -465,16 +478,26 @@ static int etm_enable_perf(struct coresight_device *csdev,
 			   struct coresight_path *path)
 {
 	struct etm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
+	int ret;
 
 	if (WARN_ON_ONCE(drvdata->cpu != smp_processor_id()))
 		return -EINVAL;
 
+	if (!coresight_take_mode(csdev, CS_MODE_PERF))
+		return -EBUSY;
+
 	/* Configure the tracer based on the session's specifics */
 	etm_parse_event_config(drvdata, event);
 	drvdata->traceid = path->trace_id;
 
 	/* And enable it */
-	return etm_enable_hw(drvdata);
+	ret = etm_enable_hw(drvdata);
+
+	/* Failed to start tracer; roll back to DISABLED mode */
+	if (ret)
+		coresight_set_mode(csdev, CS_MODE_DISABLED);
+
+	return ret;
 }
 
 static int etm_enable_sysfs(struct coresight_device *csdev, struct coresight_path *path)
@@ -494,7 +517,7 @@ static int etm_enable_sysfs(struct coresight_device *csdev, struct coresight_pat
 	if (cpu_online(drvdata->cpu)) {
 		arg.drvdata = drvdata;
 		ret = smp_call_function_single(drvdata->cpu,
-					       etm_enable_hw_smp_call, &arg, 1);
+					       etm_enable_sysfs_smp_call, &arg, 1);
 		if (!ret)
 			ret = arg.rc;
 		if (!ret)
@@ -517,12 +540,6 @@ static int etm_enable(struct coresight_device *csdev, struct perf_event *event,
 		      enum cs_mode mode, struct coresight_path *path)
 {
 	int ret;
-	struct etm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
-
-	if (!coresight_take_mode(csdev, mode)) {
-		/* Someone is already using the tracer */
-		return -EBUSY;
-	}
 
 	switch (mode) {
 	case CS_MODE_SYSFS:
@@ -535,17 +552,12 @@ static int etm_enable(struct coresight_device *csdev, struct perf_event *event,
 		ret = -EINVAL;
 	}
 
-	/* The tracer didn't start */
-	if (ret)
-		coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED);
-
 	return ret;
 }
 
-static void etm_disable_hw(void *info)
+static void etm_disable_hw(struct etm_drvdata *drvdata)
 {
 	int i;
-	struct etm_drvdata *drvdata = info;
 	struct etm_config *config = &drvdata->config;
 	struct coresight_device *csdev = drvdata->csdev;
 
@@ -567,6 +579,15 @@ static void etm_disable_hw(void *info)
 		"cpu: %d disable smp call done\n", drvdata->cpu);
 }
 
+static void etm_disable_sysfs_smp_call(void *info)
+{
+	struct etm_drvdata *drvdata = info;
+
+	etm_disable_hw(drvdata);
+
+	coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED);
+}
+
 static void etm_disable_perf(struct coresight_device *csdev)
 {
 	struct etm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
@@ -588,6 +609,8 @@ static void etm_disable_perf(struct coresight_device *csdev)
 
 	CS_LOCK(drvdata->csa.base);
 
+	coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED);
+
 	/*
 	 * perf will release trace ids when _free_aux()
 	 * is called at the end of the session
@@ -612,7 +635,8 @@ static void etm_disable_sysfs(struct coresight_device *csdev)
 	 * Executing etm_disable_hw on the cpu whose ETM is being disabled
 	 * ensures that register writes occur when cpu is powered.
 	 */
-	smp_call_function_single(drvdata->cpu, etm_disable_hw, drvdata, 1);
+	smp_call_function_single(drvdata->cpu, etm_disable_sysfs_smp_call,
+				 drvdata, 1);
 
 	spin_unlock(&drvdata->spinlock);
 	cpus_read_unlock();
@@ -652,9 +676,6 @@ static void etm_disable(struct coresight_device *csdev,
 		WARN_ON_ONCE(mode);
 		return;
 	}
-
-	if (mode)
-		coresight_set_mode(csdev, CS_MODE_DISABLED);
 }
 
 static const struct coresight_ops_source etm_source_ops = {

-- 
2.34.1