Re: [PATCH v5 07/12] coresight: etm4x: fix inconsistencies with sysfs configuration

Jie Gan
2026-04-16T04:35:56Z

On 4/16/2026 12:55 AM, Yeoreum Yun wrote:
> The current ETM4x configuration via sysfs can lead to
> several inconsistencies:
>
> - If the configuration is modified via sysfs while a perf session is
> active, the running configuration may differ before a sched-out and
> after a subsequent sched-in.
>
> - If a perf session and a sysfs session enable tracing concurrently,
> the configuration from configfs may become corrupted.
>
> - There is a risk of corrupting drvdata->config if a perf session enables
> tracing while cscfg_csdev_disable_active_config() is being handled in
> etm4_disable_sysfs().
>
> To resolve these issues, separate the configuration into:
>
> - active_config: the configuration applied to the current session
> - config: the configuration set via sysfs
>
> Additionally:
>
> - Apply the configuration from configfs after taking the appropriate mode.
>
> - Since active_config and related fields are accessed only by the local CPU
> in etm4_enable/disable_sysfs_smp_call() (similar to perf enable/disable),
> remove the lock/unlock from the sysfs enable/disable path and
> startup/dying_cpu except when to access config fields.
>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---

<...>

> @@ -618,23 +624,45 @@ 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;
>
> 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 */
> + if (arg->cfg_hash) {
> + arg->rc = cscfg_csdev_enable_active_config(csdev,
> + arg->cfg_hash,
> + arg->preset);
> + if (arg->rc)
> + goto err;
> + }
> +
> + drvdata->trcid = arg->trace_id;
> +
> + /* Tracer will never be paused in sysfs mode */
> + drvdata->paused = false;
> +
> + arg->rc = etm4_enable_hw(drvdata);
> if (arg->rc)
> - coresight_set_mode(csdev, CS_MODE_DISABLED);

needs disable the active config in error path:
cscfg_csdev_disable_active_config(drvdata->csdev);

Thanks,
Jie

> + goto err;
> +
> + drvdata->sticky_enable = true;
> +
> + return;
> +err:
> + /* The tracer didn't start */
> + coresight_set_mode(csdev, CS_MODE_DISABLED);
> }
>
> /*
> @@ -672,7 +700,7 @@ static int etm4_config_timestamp_event(struct etmv4_drvdata *drvdata,
> int ctridx;
> int rselector;
> const struct etmv4_caps *caps = &drvdata->caps;
> - struct etmv4_config *config = &drvdata->config;
> + struct etmv4_config *config = &drvdata->active_config;
>
> /* No point in trying if we don't have at least one counter */
> if (!caps->nr_cntr)
> @@ -756,7 +784,7 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
> int ret = 0;
> struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> const struct etmv4_caps *caps = &drvdata->caps;
> - struct etmv4_config *config = &drvdata->config;
> + struct etmv4_config *config = &drvdata->active_config;
> struct perf_event_attr max_timestamp = {
> .ATTR_CFG_FLD_timestamp_CFG = U64_MAX,
> };
> @@ -918,40 +946,29 @@ static int etm4_enable_sysfs(struct coresight_device *csdev, struct coresight_pa
>
> /* enable any config activated by configfs */
> cscfg_config_sysfs_get_active_cfg(&cfg_hash, &preset);
> - if (cfg_hash) {
> - ret = cscfg_csdev_enable_active_config(csdev, cfg_hash, preset);
> - if (ret) {
> - etm4_release_trace_id(drvdata);
> - return ret;
> - }
> - }
> -
> - raw_spin_lock(&drvdata->spinlock);
> -
> - drvdata->trcid = path->trace_id;
> -
> - /* Tracer will never be paused in sysfs mode */
> - drvdata->paused = false;
>
> /*
> * Executing etm4_enable_hw on the cpu whose ETM is being enabled
> * ensures that register writes occur when cpu is powered.
> */
> arg.drvdata = drvdata;
> + arg.cfg_hash = cfg_hash;
> + arg.preset = preset;
> + arg.trace_id = path->trace_id;
> +
> + raw_spin_lock(&drvdata->spinlock);
> + arg.config = drvdata->config;
> + raw_spin_unlock(&drvdata->spinlock);
> +
> ret = smp_call_function_single(drvdata->cpu,
> etm4_enable_sysfs_smp_call, &arg, 1);
> if (!ret)
> ret = arg.rc;
> if (!ret)
> - drvdata->sticky_enable = true;
> -
> - if (ret)
> + dev_dbg(&csdev->dev, "ETM tracing enabled\n");
> + else
> etm4_release_trace_id(drvdata);
>
> - raw_spin_unlock(&drvdata->spinlock);
> -
> - if (!ret)
> - dev_dbg(&csdev->dev, "ETM tracing enabled\n");
> return ret;
> }
>
> @@ -1038,7 +1055,7 @@ static void etm4_disable_hw(struct etmv4_drvdata *drvdata)
> {
> u32 control;
> const struct etmv4_caps *caps = &drvdata->caps;
> - struct etmv4_config *config = &drvdata->config;
> + struct etmv4_config *config = &drvdata->active_config;
> struct coresight_device *csdev = drvdata->csdev;
> struct csdev_access *csa = &csdev->access;
> int i;
> @@ -1074,6 +1091,8 @@ static void etm4_disable_sysfs_smp_call(void *info)
>
> etm4_disable_hw(drvdata);
>
> + cscfg_csdev_disable_active_config(drvdata->csdev);
> +
> coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED);
> }
>
> @@ -1124,7 +1143,6 @@ static void etm4_disable_sysfs(struct coresight_device *csdev)
> * DYING hotplug callback is serviced by the ETM driver.
> */
> cpus_read_lock();
> - raw_spin_lock(&drvdata->spinlock);
>
> /*
> * Executing etm4_disable_hw on the cpu whose ETM is being disabled
> @@ -1133,10 +1151,6 @@ static void etm4_disable_sysfs(struct coresight_device *csdev)
> smp_call_function_single(drvdata->cpu, etm4_disable_sysfs_smp_call,
> drvdata, 1);
>
> - raw_spin_unlock(&drvdata->spinlock);
> -
> - cscfg_csdev_disable_active_config(csdev);
> -
> cpus_read_unlock();
>
> /*
> @@ -1379,6 +1393,7 @@ static void etm4_init_arch_data(void *info)
> struct etm4_init_arg *init_arg = info;
> struct etmv4_drvdata *drvdata;
> struct etmv4_caps *caps;
> + struct etmv4_config *config;
> struct csdev_access *csa;
> struct device *dev = init_arg->dev;
> int i;
> @@ -1386,6 +1401,7 @@ static void etm4_init_arch_data(void *info)
> drvdata = dev_get_drvdata(init_arg->dev);
> caps = &drvdata->caps;
> csa = init_arg->csa;
> + config = &drvdata->active_config;
>
> /*
> * If we are unable to detect the access mechanism,
> @@ -1446,7 +1462,7 @@ static void etm4_init_arch_data(void *info)
>
> /* EXLEVEL_S, bits[19:16] Secure state instruction tracing */
> caps->s_ex_level = FIELD_GET(TRCIDR3_EXLEVEL_S_MASK, etmidr3);
> - drvdata->config.s_ex_level = caps->s_ex_level;
> + config->s_ex_level = caps->s_ex_level;
> /* EXLEVEL_NS, bits[23:20] Non-secure state instruction tracing */
> caps->ns_ex_level = FIELD_GET(TRCIDR3_EXLEVEL_NS_MASK, etmidr3);
> /*
> @@ -1692,7 +1708,7 @@ static void etm4_set_default(struct etmv4_config *config)
> static int etm4_get_next_comparator(struct etmv4_drvdata *drvdata, u32 type)
> {
> int nr_comparator, index = 0;
> - struct etmv4_config *config = &drvdata->config;
> + struct etmv4_config *config = &drvdata->active_config;
>
> /*
> * nr_addr_cmp holds the number of comparator _pair_, so time 2
> @@ -1733,7 +1749,7 @@ static int etm4_set_event_filters(struct etmv4_drvdata *drvdata,
> {
> int i, comparator, ret = 0;
> u64 address;
> - struct etmv4_config *config = &drvdata->config;
> + struct etmv4_config *config = &drvdata->active_config;
> struct etm_filters *filters = event->hw.addr_filters;
>
> if (!filters)
> @@ -1851,13 +1867,11 @@ static int etm4_starting_cpu(unsigned int cpu)
> if (!etmdrvdata[cpu])
> return 0;
>
> - raw_spin_lock(&etmdrvdata[cpu]->spinlock);
> if (!etmdrvdata[cpu]->os_unlock)
> etm4_os_unlock(etmdrvdata[cpu]);
>
> if (coresight_get_mode(etmdrvdata[cpu]->csdev))
> etm4_enable_hw(etmdrvdata[cpu]);
> - raw_spin_unlock(&etmdrvdata[cpu]->spinlock);
> return 0;
> }
>
> @@ -1866,10 +1880,8 @@ static int etm4_dying_cpu(unsigned int cpu)
> if (!etmdrvdata[cpu])
> return 0;
>
> - raw_spin_lock(&etmdrvdata[cpu]->spinlock);
> if (coresight_get_mode(etmdrvdata[cpu]->csdev))
> etm4_disable_hw(etmdrvdata[cpu]);
> - raw_spin_unlock(&etmdrvdata[cpu]->spinlock);
> return 0;
> }
>
> @@ -2255,7 +2267,8 @@ static int etm4_add_coresight_dev(struct etm4_init_arg *init_arg)
> if (!desc.name)
> return -ENOMEM;
>
> - etm4_set_default(&drvdata->config);
> + etm4_set_default(&drvdata->active_config);
> + drvdata->config = drvdata->active_config;
>
> pdata = coresight_get_platform_data(dev);
> if (IS_ERR(pdata))
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> index cbd8890d166a..9b50aaa368cf 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> @@ -1069,6 +1069,7 @@ struct etmv4_save_state {
> * allows tracing at all ELs. We don't want to compute this
> * at runtime, due to the additional setting of TRFCR_CX when
> * in EL2. Otherwise, 0.
> + * @active_config: structure holding current applied configuration parameters.
> * @config: structure holding configuration parameters.
> * @save_state: State to be preserved across power loss
> * @paused: Indicates if the trace unit is paused.
> @@ -1089,6 +1090,7 @@ struct etmv4_drvdata {
> bool os_unlock : 1;
> bool paused : 1;
> u64 trfcr;
> + struct etmv4_config active_config;
> struct etmv4_config config;
> struct etmv4_save_state *save_state;
> DECLARE_BITMAP(arch_features, ETM4_IMPDEF_FEATURE_MAX);