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, 29 insertions, 6 deletions

diff --git a/drivers/hwtracing/coresight/coresight-replicator.c b/drivers/hwtracing/coresight/coresight-replicator.c
index b29ba640eb25..43304196a1a6 100644
--- a/drivers/hwtracing/coresight/coresight-replicator.c
+++ b/drivers/hwtracing/coresight/coresight-replicator.c
@@ -31,11 +31,13 @@ DEFINE_CORESIGHT_DEVLIST(replicator_devs, "replicator");
  *		whether this one is programmable or not.
  * @atclk:	optional clock for the core parts of the replicator.
  * @csdev:	component vitals needed by the framework
+ * @spinlock:	serialize enable/disable operations.
  */
 struct replicator_drvdata {
 	void __iomem		*base;
 	struct clk		*atclk;
 	struct coresight_device	*csdev;
+	spinlock_t		spinlock;
 };
 
 static void dynamic_replicator_reset(struct replicator_drvdata *drvdata)
@@ -97,10 +99,22 @@ static int replicator_enable(struct coresight_device *csdev, int inport,
 {
 	int rc = 0;
 	struct replicator_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
-
-	if (drvdata->base)
-		rc = dynamic_replicator_enable(drvdata, inport, outport);
+	unsigned long flags;
+	bool first_enable = false;
+
+	spin_lock_irqsave(&drvdata->spinlock, flags);
+	if (atomic_read(&csdev->refcnt[outport]) == 0) {
+		if (drvdata->base)
+			rc = dynamic_replicator_enable(drvdata, inport,
+						       outport);
+		if (!rc)
+			first_enable = true;
+	}
 	if (!rc)
+		atomic_inc(&csdev->refcnt[outport]);
+	spin_unlock_irqrestore(&drvdata->spinlock, flags);
+
+	if (first_enable)
 		dev_dbg(&csdev->dev, "REPLICATOR enabled\n");
 	return rc;
 }
@@ -137,10 +151,19 @@ static void replicator_disable(struct coresight_device *csdev, int inport,
 			       int outport)
 {
 	struct replicator_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[outport]) == 0) {
+		if (drvdata->base)
+			dynamic_replicator_disable(drvdata, inport, outport);
+		last_disable = true;
+	}
+	spin_unlock_irqrestore(&drvdata->spinlock, flags);
 
-	if (drvdata->base)
-		dynamic_replicator_disable(drvdata, inport, outport);
-	dev_dbg(&csdev->dev, "REPLICATOR disabled\n");
+	if (last_disable)
+		dev_dbg(&csdev->dev, "REPLICATOR disabled\n");
 }
 
 static const struct coresight_ops_link replicator_link_ops = {