linux-kernel - Re: [PATCH v2 1/3] coresight: cti: Prevent negative values of enable count

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Message-ID: <6e6272ae-1aff-335e-4390-09c7d522dd46@arm.com>
Date:   Fri, 6 Jan 2023 16:41:32 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     James Clark <james.clark@....com>, coresight@...ts.linaro.org,
        quic_jinlmao@...cinc.com, mike.leach@...aro.org
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] coresight: cti: Prevent negative values of enable
 count

Hi James,

Thanks for fixing this.

On 06/01/2023 15:23, James Clark wrote:
> Writing 0 to the enable control repeatedly results in a negative value
> for enable_req_count. After this, writing 1 to the enable control
> appears to not work until the count returns to positive.
> 
> Change it so that it's impossible for enable_req_count to be < 0.

I prefer rephrasing the following :

> Returning an error will also allow us to decide whether to call
> runtime_pm_put() or not in the following commit.

"Return an error to indicate the disable request was invalid"

and don't mention the forward dependency.

> 

May be also add ?

Fixes: 835d722ba10a ("coresight: cti: Initial CoreSight CTI Driver")

> Signed-off-by: James Clark <james.clark@....com>

Rest looks fine to me.

Suzuki


> ---
>   drivers/hwtracing/coresight/coresight-cti-core.c | 11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-cti-core.c b/drivers/hwtracing/coresight/coresight-cti-core.c
> index d2cf4f4848e1..838872f2484d 100644
> --- a/drivers/hwtracing/coresight/coresight-cti-core.c
> +++ b/drivers/hwtracing/coresight/coresight-cti-core.c
> @@ -151,9 +151,16 @@ static int cti_disable_hw(struct cti_drvdata *drvdata)
>   {
>   	struct cti_config *config = &drvdata->config;
>   	struct coresight_device *csdev = drvdata->csdev;
> +	int ret = 0;
>   
>   	spin_lock(&drvdata->spinlock);
>   
> +	/* don't allow negative refcounts, return an error */
> +	if (!atomic_read(&drvdata->config.enable_req_count)) {
> +		ret = -EINVAL;
> +		goto cti_not_disabled;
> +	}
> +
>   	/* check refcount - disable on 0 */
>   	if (atomic_dec_return(&drvdata->config.enable_req_count) > 0)
>   		goto cti_not_disabled;
> @@ -171,12 +178,12 @@ static int cti_disable_hw(struct cti_drvdata *drvdata)
>   	coresight_disclaim_device_unlocked(csdev);
>   	CS_LOCK(drvdata->base);
>   	spin_unlock(&drvdata->spinlock);
> -	return 0;
> +	return ret;
>   
>   	/* not disabled this call */
>   cti_not_disabled:
>   	spin_unlock(&drvdata->spinlock);
> -	return 0;
> +	return ret;
>   }
>   
>   void cti_write_single_reg(struct cti_drvdata *drvdata, int offset, u32 value)