From: James Clark <james.clark@linaro.org>
To: Jie Gan <jie.gan@oss.qualcomm.com>
Cc: coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Mike Leach <mike.leach@arm.com>, 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>
Subject: Re: [PATCH] coresight: tpda: fix race between refcnt check and register access
Date: Wed, 8 Apr 2026 14:27:54 +0100 [thread overview]
Message-ID: <511c0ae1-6ad4-4607-92b5-4ea2be2ee04d@linaro.org> (raw)
In-Reply-To: <20260408-fix-race-condition-issue-v1-1-9a148d07e08f@oss.qualcomm.com>
On 08/04/2026 2:23 pm, Jie Gan wrote:
> 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>
Reviewed-by: James Clark <james.clark@linaro.org>
> ---
> 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,
prev parent reply other threads:[~2026-04-08 13:28 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-08 13:23 [PATCH] coresight: tpda: fix race between refcnt check and register access Jie Gan
2026-04-08 13:27 ` James Clark [this message]
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