linux-kernel - [PATCH v2 1/3] coresight: catu: Introduce refcount and spinlock for enabling/disabling

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Message-ID: <20250402011832.2970072-2-yabinc@google.com>
Date: Tue,  1 Apr 2025 18:18:30 -0700
From: Yabin Cui <yabinc@...gle.com>
To: Suzuki K Poulose <suzuki.poulose@....com>, Mike Leach <mike.leach@...aro.org>, 
	James Clark <james.clark@...aro.org>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, Yabin Cui <yabinc@...gle.com>
Subject: [PATCH v2 1/3] coresight: catu: Introduce refcount and spinlock for enabling/disabling

When tracing ETM data on multiple CPUs concurrently via the
perf interface, the CATU device is shared across different CPU
paths. This can lead to race conditions when multiple CPUs attempt
to enable or disable the CATU device simultaneously.

To address these race conditions, this patch introduces the
following changes:

1. The enable and disable operations for the CATU device are not
   reentrant. Therefore, a spinlock is added to ensure that only
   one CPU can enable or disable a given CATU device at any point
   in time.

2. A reference counter is used to manage the enable/disable state
   of the CATU device. The device is enabled when the first CPU
   requires it and is only disabled when the last CPU finishes
   using it. This ensures the device remains active as long as at
   least one CPU needs it.

Signed-off-by: Yabin Cui <yabinc@...gle.com>
---
 drivers/hwtracing/coresight/coresight-catu.c | 27 ++++++++++++++------
 drivers/hwtracing/coresight/coresight-catu.h |  1 +
 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-catu.c b/drivers/hwtracing/coresight/coresight-catu.c
index fa170c966bc3..b1d490dd7249 100644
--- a/drivers/hwtracing/coresight/coresight-catu.c
+++ b/drivers/hwtracing/coresight/coresight-catu.c
@@ -458,12 +458,17 @@ static int catu_enable_hw(struct catu_drvdata *drvdata, enum cs_mode cs_mode,
 static int catu_enable(struct coresight_device *csdev, enum cs_mode mode,
 		       void *data)
 {
-	int rc;
+	int rc = 0;
 	struct catu_drvdata *catu_drvdata = csdev_to_catu_drvdata(csdev);
+	guard(raw_spinlock_irqsave)(&catu_drvdata->spinlock);
 
-	CS_UNLOCK(catu_drvdata->base);
-	rc = catu_enable_hw(catu_drvdata, mode, data);
-	CS_LOCK(catu_drvdata->base);
+	if (csdev->refcnt == 0) {
+		CS_UNLOCK(catu_drvdata->base);
+		rc = catu_enable_hw(catu_drvdata, mode, data);
+		CS_LOCK(catu_drvdata->base);
+	}
+	if (!rc)
+		csdev->refcnt++;
 	return rc;
 }
 
@@ -486,12 +491,17 @@ static int catu_disable_hw(struct catu_drvdata *drvdata)
 
 static int catu_disable(struct coresight_device *csdev, void *__unused)
 {
-	int rc;
+	int rc = 0;
 	struct catu_drvdata *catu_drvdata = csdev_to_catu_drvdata(csdev);
+	guard(raw_spinlock_irqsave)(&catu_drvdata->spinlock);
 
-	CS_UNLOCK(catu_drvdata->base);
-	rc = catu_disable_hw(catu_drvdata);
-	CS_LOCK(catu_drvdata->base);
+	if (--csdev->refcnt == 0) {
+		CS_UNLOCK(catu_drvdata->base);
+		rc = catu_disable_hw(catu_drvdata);
+		CS_LOCK(catu_drvdata->base);
+	} else {
+		rc = -EBUSY;
+	}
 	return rc;
 }
 
@@ -550,6 +560,7 @@ static int __catu_probe(struct device *dev, struct resource *res)
 	dev->platform_data = pdata;
 
 	drvdata->base = base;
+	raw_spin_lock_init(&drvdata->spinlock);
 	catu_desc.access = CSDEV_ACCESS_IOMEM(base);
 	catu_desc.pdata = pdata;
 	catu_desc.dev = dev;
diff --git a/drivers/hwtracing/coresight/coresight-catu.h b/drivers/hwtracing/coresight/coresight-catu.h
index 141feac1c14b..755776cd19c5 100644
--- a/drivers/hwtracing/coresight/coresight-catu.h
+++ b/drivers/hwtracing/coresight/coresight-catu.h
@@ -65,6 +65,7 @@ struct catu_drvdata {
 	void __iomem *base;
 	struct coresight_device *csdev;
 	int irq;
+	raw_spinlock_t spinlock;
 };
 
 #define CATU_REG32(name, offset)					\
-- 
2.49.0.472.ge94155a9ec-goog