coresight: Serialize enabling/disabling a link device.

When tracing etm data of multiple threads on multiple cpus through perf
interface, some link devices are shared between paths of different cpus.
It creates race conditions when different cpus wants to enable/disable
the same link device at the same time.

Example 1:
Two cpus want to enable different ports of a coresight funnel, thus
calling the funnel enable operation at the same time. But the funnel
enable operation isn't reentrantable.

Example 2:
For an enabled coresight dynamic replicator with refcnt=1, one cpu wants
to disable it, while another cpu wants to enable it. Ideally we still have
an enabled replicator with refcnt=1 at the end. But in reality the result
is uncertain.

Since coresight devices claim themselves when enabled for self-hosted
usage, the race conditions above usually make the link devices not usable
after many cycles.

To fix the race conditions, this patch uses spinlocks to serialize
enabling/disabling link devices.

Fixes: a06ae8609b3d ("coresight: add CoreSight core layer framework")
Signed-off-by: Yabin Cui <yabinc@google.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: stable <stable@vger.kernel.org> # 5.3
Link: https://lore.kernel.org/r/20191104181251.26732-14-mathieu.poirier@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 28 insertions, 8 deletions

diff --git a/drivers/hwtracing/coresight/coresight-funnel.c b/drivers/hwtracing/coresight/coresight-funnel.c
index 05f7896c3a01..b605889b507a 100644
--- a/drivers/hwtracing/coresight/coresight-funnel.c
+++ b/drivers/hwtracing/coresight/coresight-funnel.c
@@ -38,12 +38,14 @@ DEFINE_CORESIGHT_DEVLIST(funnel_devs, "funnel");
  * @atclk:	optional clock for the core parts of the funnel.
  * @csdev:	component vitals needed by the framework.
  * @priority:	port selection order.
+ * @spinlock:	serialize enable/disable operations.
  */
 struct funnel_drvdata {
 	void __iomem		*base;
 	struct clk		*atclk;
 	struct coresight_device	*csdev;
 	unsigned long		priority;
+	spinlock_t		spinlock;
 };
 
 static int dynamic_funnel_enable_hw(struct funnel_drvdata *drvdata, int port)
@@ -76,11 +78,21 @@ static int funnel_enable(struct coresight_device *csdev, int inport,
 {
 	int rc = 0;
 	struct funnel_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
-
-	if (drvdata->base)
-		rc = dynamic_funnel_enable_hw(drvdata, inport);
-
+	unsigned long flags;
+	bool first_enable = false;
+
+	spin_lock_irqsave(&drvdata->spinlock, flags);
+	if (atomic_read(&csdev->refcnt[inport]) == 0) {
+		if (drvdata->base)
+			rc = dynamic_funnel_enable_hw(drvdata, inport);
+		if (!rc)
+			first_enable = true;
+	}
 	if (!rc)
+		atomic_inc(&csdev->refcnt[inport]);
+	spin_unlock_irqrestore(&drvdata->spinlock, flags);
+
+	if (first_enable)
 		dev_dbg(&csdev->dev, "FUNNEL inport %d enabled\n", inport);
 	return rc;
 }
@@ -107,11 +119,19 @@ static void funnel_disable(struct coresight_device *csdev, int inport,
 			   int outport)
 {
 	struct funnel_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
+	unsigned long flags;
+	bool last_disable = false;
+
+	spin_lock_irqsave(&drvdata->spinlock, flags);
+	if (atomic_dec_return(&csdev->refcnt[inport]) == 0) {
+		if (drvdata->base)
+			dynamic_funnel_disable_hw(drvdata, inport);
+		last_disable = true;
+	}
+	spin_unlock_irqrestore(&drvdata->spinlock, flags);
 
-	if (drvdata->base)
-		dynamic_funnel_disable_hw(drvdata, inport);
-
-	dev_dbg(&csdev->dev, "FUNNEL inport %d disabled\n", inport);
+	if (last_disable)
+		dev_dbg(&csdev->dev, "FUNNEL inport %d disabled\n", inport);
 }
 
 static const struct coresight_ops_link funnel_link_ops = {