From: Jie Gan <jie.gan@oss.qualcomm.com>
To: Suzuki K Poulose <suzuki.poulose@arm.com>,
Mike Leach <mike.leach@arm.com>,
James Clark <james.clark@linaro.org>, Leo Yan <leo.yan@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Tingwei Zhang <tingwei.zhang@oss.qualcomm.com>,
Tao Zhang <tao.zhang@oss.qualcomm.com>
Cc: coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Jie Gan <jie.gan@oss.qualcomm.com>
Subject: [PATCH] coresight: tpda: fix race between refcnt check and register access
Date: Wed, 08 Apr 2026 21:23:44 +0800 [thread overview]
Message-ID: <20260408-fix-race-condition-issue-v1-1-9a148d07e08f@oss.qualcomm.com> (raw)
Several sysfs show/store handlers check csdev->refcnt before acquiring
the spinlock, then access hardware registers inside the lock. This is
a race: between the check and the lock acquisition, the following can
occur on another CPU:
CPU 0 (sysfs reader) CPU 1 (disable path)
───────────────────────────── ──────────────────────────────────
refcnt == 1, check passes
[waiting for spinlock] tpda_disable(): refcnt → 0
debug clock disabled
spinlock acquired
readl_relaxed() ← FAULT/hang
tpda_disable() decrements csdev->refcnt under the same spinlock, so
moving the refcnt check inside the lock closes the race.
Fix all six affected sysfs handlers: global_flush_req_show/store,
syncr_mode_show, syncr_count_show, and port_flush_req_show/store.
Fixes: 8e1c358a3b0e ("coresight: tpda: add global_flush_req sysfs node")
Fixes: 33f04ead7c49 ("coresight: tpda: add logic to configure TPDA_SYNCR register")
Fixes: a089d585a7f4 ("coresight: tpda: add sysfs node to flush specific port")
Signed-off-by: Jie Gan <jie.gan@oss.qualcomm.com>
---
drivers/hwtracing/coresight/coresight-tpda.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/drivers/hwtracing/coresight/coresight-tpda.c b/drivers/hwtracing/coresight/coresight-tpda.c
index 89c8f71f0aff..63a979312463 100644
--- a/drivers/hwtracing/coresight/coresight-tpda.c
+++ b/drivers/hwtracing/coresight/coresight-tpda.c
@@ -360,10 +360,10 @@ static ssize_t global_flush_req_show(struct device *dev,
struct tpda_drvdata *drvdata = dev_get_drvdata(dev->parent);
unsigned long val;
+ guard(spinlock)(&drvdata->spinlock);
if (!drvdata->csdev->refcnt)
return -EINVAL;
- guard(spinlock)(&drvdata->spinlock);
val = readl_relaxed(drvdata->base + TPDA_CR);
/* read global_flush_req bit */
val &= TPDA_CR_FLREQ;
@@ -382,10 +382,13 @@ static ssize_t global_flush_req_store(struct device *dev,
if (kstrtoul(buf, 0, &val))
return -EINVAL;
- if (!drvdata->csdev->refcnt || !val)
+ if (!val)
return -EINVAL;
guard(spinlock)(&drvdata->spinlock);
+ if (!drvdata->csdev->refcnt)
+ return -EINVAL;
+
val = readl_relaxed(drvdata->base + TPDA_CR);
/* set global_flush_req bit */
val |= TPDA_CR_FLREQ;
@@ -404,10 +407,10 @@ static ssize_t syncr_mode_show(struct device *dev,
struct tpda_drvdata *drvdata = dev_get_drvdata(dev->parent);
unsigned long val, syncr_val;
+ guard(spinlock)(&drvdata->spinlock);
if (!drvdata->csdev->refcnt)
return -EINVAL;
- guard(spinlock)(&drvdata->spinlock);
syncr_val = readl_relaxed(drvdata->base + TPDA_SYNCR);
val = FIELD_GET(TPDA_SYNCR_MODE_CTRL_MASK, syncr_val);
@@ -440,10 +443,10 @@ static ssize_t syncr_count_show(struct device *dev,
struct tpda_drvdata *drvdata = dev_get_drvdata(dev->parent);
unsigned long val;
+ guard(spinlock)(&drvdata->spinlock);
if (!drvdata->csdev->refcnt)
return -EINVAL;
- guard(spinlock)(&drvdata->spinlock);
val = readl_relaxed(drvdata->base + TPDA_SYNCR);
val &= TPDA_SYNCR_COUNT_MASK;
@@ -478,10 +481,10 @@ static ssize_t port_flush_req_show(struct device *dev,
struct tpda_drvdata *drvdata = dev_get_drvdata(dev->parent);
unsigned long val;
+ guard(spinlock)(&drvdata->spinlock);
if (!drvdata->csdev->refcnt)
return -EINVAL;
- guard(spinlock)(&drvdata->spinlock);
val = readl_relaxed(drvdata->base + TPDA_FLUSH_CR);
return sysfs_emit(buf, "0x%lx\n", val);
@@ -498,10 +501,13 @@ static ssize_t port_flush_req_store(struct device *dev,
if (kstrtou32(buf, 0, &val))
return -EINVAL;
- if (!drvdata->csdev->refcnt || !val)
+ if (!val)
return -EINVAL;
guard(spinlock)(&drvdata->spinlock);
+ if (!drvdata->csdev->refcnt)
+ return -EINVAL;
+
CS_UNLOCK(drvdata->base);
writel_relaxed(val, drvdata->base + TPDA_FLUSH_CR);
CS_LOCK(drvdata->base);
---
base-commit: f3e6330d7fe42b204af05a2dbc68b379e0ad179e
change-id: 20260408-fix-race-condition-issue-d44203254b87
Best regards,
--
Jie Gan <jie.gan@oss.qualcomm.com>
next reply other threads:[~2026-04-08 13:24 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-08 13:23 Jie Gan [this message]
2026-04-08 13:27 ` James Clark
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