linux-kernel - Re: [PATCH V2 11/15] coresight: tmc: make sysFS and Perf mode mutually exclusive

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Date:	Tue, 19 Apr 2016 14:42:30 +0100
From:	Suzuki K Poulose <Suzuki.Poulose@....com>
To:	Mathieu Poirier <mathieu.poirier@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 11/15] coresight: tmc: make sysFS and Perf mode
 mutually exclusive

On 12/04/16 18:54, Mathieu Poirier wrote:
> The sysFS and Perf access methods can't be allowed to interfere
> with one another.  As such introducing guards to access
> functions that prevents moving forward if a TMC is already
> being used.
>
> Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> ---
>   drivers/hwtracing/coresight/coresight-tmc-etf.c | 59 +++++++++++++++++++++-
>   drivers/hwtracing/coresight/coresight-tmc-etr.c | 67 +++++++++++++++++++++++--
>   2 files changed, 119 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> index 9b4cdaed09f5..50d32e8ef4ea 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> @@ -111,7 +111,7 @@ static void tmc_etf_disable_hw(struct tmc_drvdata *drvdata)
>   	CS_LOCK(drvdata->base);
>   }
>
> -static int tmc_enable_etf_sink(struct coresight_device *csdev, u32 mode)
> +static int tmc_enable_etf_sink_sysfs(struct coresight_device *csdev, u32 mode)
>   {
>   	bool allocated = false;
>   	char *buf = NULL;
> @@ -189,6 +189,53 @@ out:
>   	return 0;
>   }
>
> +static int tmc_enable_etf_sink_perf(struct coresight_device *csdev, u32 mode)
> +{
> +	int ret = 0;
> +	u32 val;

To be on the safer side, I believe 'val' should be unsigned long, to match the size of local_t.

> +	unsigned long flags;
> +	struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> +
> +	 /* This shouldn't be happening */
> +	WARN_ON(mode != CS_MODE_PERF);

I think the above check, and the mode parameter itself is superfluous, given
that this is a static function used internally only for the PERF mode.
Similarly for the _sysfs version.

> +
> +	spin_lock_irqsave(&drvdata->spinlock, flags);
> +	if (drvdata->reading) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	val = local_xchg(&drvdata->mode, mode);

We should be using local_cmpxchg() here. Otherwise, we could corrupt the mode.
Similarly for the _sysfs version. I though the previous version of your series
did that.

> +	/*
> +	 * In Perf mode there can be only one writer per sink.  There
> +	 * is also no need to continue if the ETB/ETR is already operated
> +	 * from sysFS.
> +	 */
> +	if (val != CS_MODE_DISABLED) {
> +		ret = -EINVAL;
> +		goto out;
> +	}


>   static void tmc_disable_etf_sink(struct coresight_device *csdev)
>   {
>   	u32 val;
> @@ -271,6 +318,7 @@ const struct coresight_ops tmc_etf_cs_ops = {
>
>   int tmc_read_prepare_etb(struct tmc_drvdata *drvdata)
>   {
> +	u32 val;
>   	enum tmc_mode mode;
>   	int ret = 0;
>   	unsigned long flags;
> @@ -289,6 +337,13 @@ int tmc_read_prepare_etb(struct tmc_drvdata *drvdata)
>   		goto out;
>   	}
>
> +	val = local_read(&drvdata->mode);
> +	/* Don't interfere if operated from Perf */
> +	if (val == CS_MODE_PERF) {
> +		ret = -EINVAL;
> +		goto out;
> +	}

Could we get here when CS_DISABLED ? If not, we could get rid of the check
for CS_MODE_SYSFS below.

> +
>   	/* If drvdata::buf is NULL the trace data has been read already */
>   	if (drvdata->buf == NULL) {
>   		ret = -EINVAL;
> @@ -296,7 +351,7 @@ int tmc_read_prepare_etb(struct tmc_drvdata *drvdata)
>   	}
>
>   	/* Disable the TMC if need be */
> -	if (local_read(&drvdata->mode) == CS_MODE_SYSFS)
> +	if (val == CS_MODE_SYSFS)
>   		tmc_etb_disable_hw(drvdata);
See above

>   	drvdata->reading = true;
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> index de5cf0056802..04fc63d85696 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> @@ -87,7 +87,7 @@ static void tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
>   	CS_LOCK(drvdata->base);
>   }
>
> -static int tmc_enable_etr_sink(struct coresight_device *csdev, u32 mode)
> +static int tmc_enable_etr_sink_sysfs(struct coresight_device *csdev, u32 mode)
>   {
>   	bool allocated = false;
>   	u32 val;
> @@ -166,6 +166,53 @@ out:
>   	return 0;
>   }
>

> +static int tmc_enable_etr_sink_perf(struct coresight_device *csdev, u32 mode)
...

>   static void tmc_disable_etr_sink(struct coresight_device *csdev)

Same comments as for the etb side.

Suzuki

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