Re: [PATCH v12 05/14] coresight: etm3x: fix inconsistencies with sysfs configuration

[Mike Leach <mike.leach@arm.com>]

Reviewed-by: Mike Leach <mike.leach@arm.com>

On 9/24/26 18:33, Yeoreum Yun wrote:
> The current ETM3x configuration via sysfs can lead to the following
> inconsistencies:
> 
>    - If a configuration is modified via sysfs while a perf session is
>      active, the running configuration may differ between before
>      a sched-out and after a subsequent sched-in.
> 
> To resolve these issues, separate the configuration into:
> 
>    - curr_config: the configuration applied to the current session
>    - config: the configuration set via sysfs
> 
> Additionally:
> 
>    - Since curr_config and related fields are accessed only by the local CPU
>      in etm_enable/disable_sysfs_smp_call() (similar to perf enable/disable),
>      remove the lock/unlock from the sysfs enable/disable path and
>      starting/dying_cpu path except when to access config fields only.
> 
>    - Some of sysfs interface read etm register directly. To reduce lock
>      scope while the etm_enable_hw()/etm_disable_hw(), handle it via
>      IPI so that registers could be read from on proper CPU.
> 
> Fixes: 1925a470ce69 ("coresight: etm3x: splitting struct etm_drvdata")
> Tested-by: Leo Yan <leo.yan@arm.com>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
>   drivers/hwtracing/coresight/coresight-etm.h        |  4 +-
>   drivers/hwtracing/coresight/coresight-etm3x-core.c | 66 ++++++++++--------
>   .../hwtracing/coresight/coresight-etm3x-sysfs.c    | 80 +++++++++++++++-------
>   3 files changed, 98 insertions(+), 52 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm.h b/drivers/hwtracing/coresight/coresight-etm.h
> index 1d753cca2943..52f23a3c7364 100644
> --- a/drivers/hwtracing/coresight/coresight-etm.h
> +++ b/drivers/hwtracing/coresight/coresight-etm.h
> @@ -226,7 +226,8 @@ struct etm_config {
>    * @etmccr:	value of register ETMCCR.
>    * @etmccer:	value of register ETMCCER.
>    * @traceid:	value of the current ID for this component.
> - * @config:	structure holding configuration parameters.
> + * @curr_config:	structure holding current running configuration.
> + * @config:	structure holding sysfs mode configuration.
>    */
>   struct etm_drvdata {
>   	struct csdev_access		csa;
> @@ -248,6 +249,7 @@ struct etm_drvdata {
>   	u32				etmccr;
>   	u32				etmccer;
>   	u32				traceid;
> +	struct etm_config		curr_config;
>   	struct etm_config		config;
>   };
>   
> diff --git a/drivers/hwtracing/coresight/coresight-etm3x-core.c b/drivers/hwtracing/coresight/coresight-etm3x-core.c
> index 862ad0786699..dcadcc383012 100644
> --- a/drivers/hwtracing/coresight/coresight-etm3x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm3x-core.c
> @@ -308,7 +308,7 @@ void etm_config_trace_mode(struct etm_config *config)
>   static int etm_parse_event_config(struct etm_drvdata *drvdata,
>   				  struct perf_event *event)
>   {
> -	struct etm_config *config = &drvdata->config;
> +	struct etm_config *config = &drvdata->curr_config;
>   	struct perf_event_attr *attr = &event->attr;
>   	u8 ts_level;
>   
> @@ -367,7 +367,7 @@ static int etm_enable_hw(struct etm_drvdata *drvdata)
>   {
>   	int i, rc;
>   	u32 etmcr;
> -	struct etm_config *config = &drvdata->config;
> +	struct etm_config *config = &drvdata->curr_config;
>   	struct coresight_device *csdev = drvdata->csdev;
>   
>   	CS_UNLOCK(drvdata->csa.base);
> @@ -448,26 +448,22 @@ struct etm_enable_arg {
>   static void etm_enable_sysfs_smp_call(void *info)
>   {
>   	struct etm_enable_arg *arg = info;
> +	struct etm_drvdata *drvdata;
>   	struct coresight_device *csdev;
>   
>   	if (WARN_ON(!arg))
>   		return;
>   
> -	csdev = arg->drvdata->csdev;
> -	if (!coresight_take_mode(csdev, CS_MODE_SYSFS)) {
> -		/* Someone is already using the tracer */
> -		arg->rc = -EBUSY;
> -		return;
> -	}
> +	drvdata = arg->drvdata;
> +	csdev = drvdata->csdev;
>   
> -	arg->rc = etm_enable_hw(arg->drvdata);
> +	drvdata->traceid = arg->path->trace_id;
>   
> -	/* The tracer didn't start */
> -	if (arg->rc) {
> -		coresight_set_mode(csdev, CS_MODE_DISABLED);
> +	arg->rc = etm_enable_hw(arg->drvdata);
> +	if (arg->rc)
>   		return;
> -	}
>   
> +	drvdata->sticky_enable = true;
>   	csdev->path = arg->path;
>   }
>   
> @@ -512,9 +508,10 @@ static int etm_enable_sysfs(struct coresight_device *csdev, struct coresight_pat
>   	struct etm_enable_arg arg = { };
>   	int ret;
>   
> -	spin_lock(&drvdata->spinlock);
> -
> -	drvdata->traceid = path->trace_id;
> +	if (!coresight_take_mode(csdev, CS_MODE_SYSFS)) {
> +		/* Someone is already using the tracer */
> +		return -EBUSY;
> +	}
>   
>   	/*
>   	 * Configure the ETM only if the CPU is online.  If it isn't online
> @@ -523,23 +520,27 @@ static int etm_enable_sysfs(struct coresight_device *csdev, struct coresight_pat
>   	if (cpu_online(drvdata->cpu)) {
>   		arg.drvdata = drvdata;
>   		arg.path = path;
> +
> +		scoped_guard(spinlock, &drvdata->spinlock) {
> +			drvdata->curr_config = drvdata->config;
> +		}
> +
>   		ret = smp_call_function_single(drvdata->cpu,
>   					       etm_enable_sysfs_smp_call, &arg, 1);
>   		if (!ret)
>   			ret = arg.rc;
> -		if (!ret)
> -			drvdata->sticky_enable = true;
>   	} else {
>   		ret = -ENODEV;
>   	}
>   
> -	if (ret)
> +	if (!ret) {
> +		dev_dbg(&csdev->dev, "ETM tracing enabled\n");
> +	} else {
>   		etm_release_trace_id(drvdata);
> +		/* The tracer didn't start */
> +		coresight_set_mode(csdev, CS_MODE_DISABLED);
> +	}
>   
> -	spin_unlock(&drvdata->spinlock);
> -
> -	if (!ret)
> -		dev_dbg(&csdev->dev, "ETM tracing enabled\n");
>   	return ret;
>   }
>   
> @@ -565,7 +566,7 @@ static int etm_enable(struct coresight_device *csdev, struct perf_event *event,
>   static void etm_disable_hw(struct etm_drvdata *drvdata)
>   {
>   	int i;
> -	struct etm_config *config = &drvdata->config;
> +	struct etm_config *config = &drvdata->curr_config;
>   	struct coresight_device *csdev = drvdata->csdev;
>   
>   	CS_UNLOCK(drvdata->csa.base);
> @@ -593,7 +594,6 @@ static void etm_disable_sysfs_smp_call(void *info)
>   	etm_disable_hw(drvdata);
>   
>   	drvdata->csdev->path = NULL;
> -	coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED);
>   }
>   
>   static void etm_disable_perf(struct coresight_device *csdev)
> @@ -630,8 +630,9 @@ static void etm_disable_perf(struct coresight_device *csdev)
>   static void etm_disable_sysfs(struct coresight_device *csdev)
>   {
>   	struct etm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> -
> -	spin_lock(&drvdata->spinlock);
> +	struct etm_config *config = &drvdata->config;
> +	const struct etm_config *curr_config = &drvdata->curr_config;
> +	int i;
>   
>   	/*
>   	 * Executing etm_disable_hw on the cpu whose ETM is being disabled
> @@ -640,7 +641,14 @@ static void etm_disable_sysfs(struct coresight_device *csdev)
>   	smp_call_function_single(drvdata->cpu, etm_disable_sysfs_smp_call,
>   				 drvdata, 1);
>   
> -	spin_unlock(&drvdata->spinlock);
> +	/*
> +	 * Userspace may read seq_curr_state and cntr_val through sysfs
> +	 * after the sysfs-session has been disabled.
> +	 */
> +	for (i = 0; i < drvdata->nr_cntr; i++)
> +		config->cntr_val[i] = curr_config->cntr_val[i];
> +
> +	config->seq_curr_state = curr_config->seq_curr_state;
>   
>   	/*
>   	 * we only release trace IDs when resetting sysfs.
> @@ -649,6 +657,8 @@ static void etm_disable_sysfs(struct coresight_device *csdev)
>   	 * prior trace id allocation method
>   	 */
>   
> +	coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED);
> +
>   	dev_dbg(&csdev->dev, "ETM tracing disabled\n");
>   }
>   
> diff --git a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> index cdb70a4382eb..284998f18017 100644
> --- a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> +++ b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> @@ -6,10 +6,48 @@
>   
>   #include <linux/pid_namespace.h>
>   #include <linux/pm_runtime.h>
> +#include <linux/smp.h>
>   #include <linux/sysfs.h>
>   #include "coresight-etm.h"
>   #include "coresight-priv.h"
>   
> +struct etm_readl_cslocked_arg {
> +	struct etm_drvdata *drvdata;
> +	u32 off;
> +	unsigned long *val;
> +};
> +
> +static void etm_readl_cslocked_smp_call(void *info)
> +{
> +	struct etm_readl_cslocked_arg *arg = info;
> +
> +	CS_UNLOCK(arg->drvdata->csa.base);
> +	*arg->val = etm_readl(arg->drvdata, arg->off);
> +	CS_LOCK(arg->drvdata->csa.base);
> +}
> +
> +static int etm_readl_cslocked(struct etm_drvdata *drvdata, u32 off,
> +			      unsigned long *val)
> +{
> +	int ret;
> +	struct etm_readl_cslocked_arg arg;
> +
> +	ret = pm_runtime_get_sync(drvdata->csdev->dev.parent);
> +	if (ret < 0)
> +		goto out;
> +
> +	arg.drvdata = drvdata;
> +	arg.off = off;
> +	arg.val = val;
> +
> +	ret = smp_call_function_single(drvdata->cpu,
> +				       etm_readl_cslocked_smp_call,
> +				       (void *)&arg, 1);
> +out:
> +	pm_runtime_put(drvdata->csdev->dev.parent);
> +	return ret;
> +}
> +
>   static ssize_t nr_addr_cmp_show(struct device *dev,
>   				struct device_attribute *attr, char *buf)
>   {
> @@ -45,18 +83,13 @@ static DEVICE_ATTR_RO(nr_ctxid_cmp);
>   static ssize_t etmsr_show(struct device *dev,
>   			  struct device_attribute *attr, char *buf)
>   {
> -	unsigned long flags, val;
> +	int ret;
> +	unsigned long val;
>   	struct etm_drvdata *drvdata = dev_get_drvdata(dev->parent);
>   
> -	pm_runtime_get_sync(dev->parent);
> -	spin_lock_irqsave(&drvdata->spinlock, flags);
> -	CS_UNLOCK(drvdata->csa.base);
> -
> -	val = etm_readl(drvdata, ETMSR);
> -
> -	CS_LOCK(drvdata->csa.base);
> -	spin_unlock_irqrestore(&drvdata->spinlock, flags);
> -	pm_runtime_put(dev->parent);
> +	ret = etm_readl_cslocked(drvdata, ETMSR, &val);
> +	if (ret)
> +		return ret;
>   
>   	return sprintf(buf, "%#lx\n", val);
>   }
> @@ -76,7 +109,7 @@ static ssize_t reset_store(struct device *dev,
>   		return ret;
>   
>   	if (IS_ERR_OR_NULL(drvdata->csdev) ||
> -	    coresight_get_mode(drvdata->csdev))
> +	    coresight_get_mode(drvdata->csdev) == CS_MODE_SYSFS)
>   		return -EBUSY;
>   
>   	if (val) {
> @@ -721,7 +754,9 @@ static DEVICE_ATTR_RW(cntr_rld_event);
>   static ssize_t cntr_val_show(struct device *dev,
>   			     struct device_attribute *attr, char *buf)
>   {
> +	int ret;
>   	u32 val;
> +	unsigned long val2;
>   	struct etm_drvdata *drvdata = dev_get_drvdata(dev->parent);
>   	struct etm_config *config = &drvdata->config;
>   
> @@ -730,7 +765,10 @@ static ssize_t cntr_val_show(struct device *dev,
>   		val = config->cntr_val[config->cntr_idx];
>   		spin_unlock(&drvdata->spinlock);
>   	} else {
> -		val = etm_readl(drvdata, ETMCNTVRn(config->cntr_idx));
> +		ret = etm_readl_cslocked(drvdata, ETMCNTVRn(config->cntr_idx), &val2);
> +		if (ret)
> +			return ret;
> +		val = val2;
>   	}
>   
>   	return sysfs_emit(buf, "%#x\n", val);
> @@ -749,7 +787,7 @@ static ssize_t cntr_val_store(struct device *dev,
>   	if (ret)
>   		return ret;
>   	if (IS_ERR_OR_NULL(drvdata->csdev) ||
> -	    coresight_get_mode(drvdata->csdev))
> +	    coresight_get_mode(drvdata->csdev) == CS_MODE_SYSFS)
>   		return -EBUSY;
>   
>   	spin_lock(&drvdata->spinlock);
> @@ -937,7 +975,8 @@ static DEVICE_ATTR_RW(seq_13_event);
>   static ssize_t seq_curr_state_show(struct device *dev,
>   				   struct device_attribute *attr, char *buf)
>   {
> -	unsigned long val, flags;
> +	int ret;
> +	unsigned long val;
>   	struct etm_drvdata *drvdata = dev_get_drvdata(dev->parent);
>   	struct etm_config *config = &drvdata->config;
>   
> @@ -946,15 +985,10 @@ static ssize_t seq_curr_state_show(struct device *dev,
>   		goto out;
>   	}
>   
> -	pm_runtime_get_sync(dev->parent);
> -	spin_lock_irqsave(&drvdata->spinlock, flags);
> -
> -	CS_UNLOCK(drvdata->csa.base);
> -	val = (etm_readl(drvdata, ETMSQR) & ETM_SQR_MASK);
> -	CS_LOCK(drvdata->csa.base);
> -
> -	spin_unlock_irqrestore(&drvdata->spinlock, flags);
> -	pm_runtime_put(dev->parent);
> +	ret = etm_readl_cslocked(drvdata, ETMSQR, &val);
> +	if (ret)
> +		return ret;
> +	val &= ETM_SQR_MASK;
>   out:
>   	return sprintf(buf, "%#lx\n", val);
>   }
>