Re: [PATCH v3 3/5] coresight: etm4x: fix inconsistencies with sysfs configration

Yeoreum Yun
2026-04-13T07:06:38Z

Hi Jie,

> Hi Yeoreum,
>
> On 4/13/2026 1:55 AM, Yeoreum Yun wrote:
> > The current ETM4x 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.
> >
> > - If a perf session and sysfs session tries to enable concurrently,
> > configuration from configfs could be corrupted.
> >
> > - There is chance to corrupt drvdata->config if perf session tries
> > to enabled among handling cscfg_csdev_disable_active_config()
> > in etm4_disable_sysfs().
> >
> > To resolve these inconsistencies, the configuration should be separated into:
> >
> > - active_config, which is applied configuration for the current session
> > - config, which stores the settings configured via sysfs.
> >
> > and apply configuration from configfs after taking a mode.
>
> typo in subject:
> s/configration/configuration

Thanks.

>
> >
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> > ---
> > .../hwtracing/coresight/coresight-etm4x-cfg.c | 2 +-
> > .../coresight/coresight-etm4x-core.c | 74 ++++++++++++-------
> > drivers/hwtracing/coresight/coresight-etm4x.h | 2 +
> > 3 files changed, 49 insertions(+), 29 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> > index d14d7c8a23e5..0553771d04e7 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> > @@ -47,7 +47,7 @@ static int etm4_cfg_map_reg_offset(struct etmv4_drvdata *drvdata,
> > struct cscfg_regval_csdev *reg_csdev, u32 offset)
> > {
> > int err = -EINVAL, idx;
> > - struct etmv4_config *drvcfg = &drvdata->config;
> > + struct etmv4_config *drvcfg = &drvdata->active_config;
> > u32 off_mask;
>
> <...>
>
> > struct device *etm_dev = &csdev->dev;
> > struct csdev_access *csa = &csdev->access;
> > @@ -616,19 +621,36 @@ 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 = drvdata->config;
> > +
> > + if (arg->cfg_hash) {
> > + arg->rc = cscfg_csdev_enable_active_config(csdev,
> > + arg->cfg_hash,
> > + arg->preset);
> > + if (arg->rc)
>
> we need reset the mode once enable failed before return.
> coresight_set_mode(csdev, CS_MODE_DISABLED);

Good catch. also missing some fix more for deadlock.
I'll send again. Thanks!

>
> Thanks,
> Jie
>
> > + return;
> > + }
> > +
> > + drvdata->trcid = arg->trace_id;
> > +
> > + /* Tracer will never be paused in sysfs mode */
> > + drvdata->paused = false;
> > +
> > + arg->rc = etm4_enable_hw(drvdata);
> > /* The tracer didn't start */
> > if (arg->rc)
> > @@ -670,7 +692,7 @@ 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)
> > @@ -754,7 +776,7 @@ 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,
> > };
> > @@ -916,24 +938,18 @@ 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)
> > - 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;
> > +
> > ret = smp_call_function_single(drvdata->cpu,
> > etm4_enable_sysfs_smp_call, &arg, 1);
> > if (!ret)
> > @@ -1034,7 +1050,7 @@ 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;
> > @@ -1070,6 +1086,8 @@ 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);
> > }
> > @@ -1130,9 +1148,6 @@ static void etm4_disable_sysfs(struct coresight_device *csdev)
> > drvdata, 1);
> > raw_spin_unlock(&drvdata->spinlock);
> > -
> > - cscfg_csdev_disable_active_config(csdev);
> > -
> > cpus_read_unlock();
> > /*
> > @@ -1375,6 +1390,7 @@ 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;
> > @@ -1382,6 +1398,7 @@ 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,
> > @@ -1442,7 +1459,7 @@ 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);
> > /*
> > @@ -1687,7 +1704,7 @@ 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
> > @@ -1728,7 +1745,7 @@ 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)
> > @@ -2250,7 +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 3cc1ca76c933..b943c28c9c71 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);
>

--
Sincerely,
Yeoreum Yun