Re: [PATCH v8 08/13] coresight: etm4x: fix inconsistencies with sysfs configuration

[Leo Yan <leo.yan@arm.com>]

On Mon, Jun 29, 2026 at 10:00:01AM +0100, Yeoreum Yun wrote:

[...]

> @@ -619,27 +622,52 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
>  static void etm4_enable_sysfs_smp_call(void *info)
>  {
>  	struct etm4_enable_arg *arg = info;
> +	struct etmv4_drvdata *drvdata;
>  	struct coresight_device *csdev;
> +	unsigned long cfg_hash;
> +	int preset;
>  
>  	if (WARN_ON(!arg))
>  		return;
>  
> -	csdev = arg->drvdata->csdev;
> +	drvdata = arg->drvdata;
> +	csdev = drvdata->csdev;
>  	if (!coresight_take_mode(csdev, CS_MODE_SYSFS)) {
>  		/* Someone is already using the tracer */
>  		arg->rc = -EBUSY;
>  		return;
>  	}
>  
> -	arg->rc = etm4_enable_hw(arg->drvdata);
> +	drvdata->active_config = arg->config;
>  
> -	/* The tracer didn't start */
> +	/* enable any config activated by configfs */
> +	cscfg_config_sysfs_get_active_cfg(&cfg_hash, &preset);
> +	if (cfg_hash) {
> +		arg->rc = cscfg_csdev_enable_active_config(csdev,
> +							   cfg_hash,
> +							   preset);
> +		if (arg->rc)
> +			goto err;
> +	}


I try best to not paste any non-sense AI reviews, record one from
Sashiko [1]:

 | If a user writes to a sysfs attribute like pe_sel_store(), it acquires
 | drvdata->spinlock without disabling interrupts. If an IPI is then handled
 | on the same CPU, etm4_enable_sysfs_smp_call() will call
 | cscfg_csdev_enable_active_config() which attempts to acquire the exact
 | same spinlock, hanging the CPU."

The flow for acquiring drvdata->spinlock in SMP call is:

  etm4_enable_sysfs_smp_call()
    `> cscfg_csdev_enable_active_config()
         `> cscfg_csdev_enable_config()
              `> cscfg_prog_config()
                   `> cscfg_set_on_enable()
                        `> raw_spin_lock_irqsave(feat_csdev->drv_spinlock, flags);

We might expect the complaint from LOCKDEP with this patch.

To be clear, I am not object to this patch, just record in case we will
handle it later.

[1] https://sashiko.dev/#/patchset/20260629090007.1718746-1-yeoreum.yun%40arm.com