[PATCH v11 3/9] coresight: etm4x: fix inconsistencies with sysfs configuration
Mike Leach
mike.leach at arm.com
Fri Sep 18 06:49:09 PDT 2026
Hi,
On 9/15/26 12:34, 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
>
I'll add a comment about naming here - active_config is a bit overloaded
in the code as it is also used by the csconfig code to represent a
loaded and active configuration - which may at some point be applied to
the active_config above.
If active_config is for the current session then curr_config would work.
Additionally config also appears as a local pointer in many of the
functions. If this is the sysfs config then sysfs_config would work better.
This should make all the code a lot more readable, and easier to spot
exactly which config we are dealing with.
> 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.
>
> As the active_config is used for cfg-configfs, etmv4 doesn't need to set
> its lock for the cfg-configfs since the active_config is proceted by cs_mode
> otherwise it would make a possible cpu-stall when it get interrupt while
> setting the sysfs configuration.
>
> Therefore, set the drv_spinlock for cfg-configfs as NULL and
> let the cfg-configfs disable irq without grap drv_spinlock when it is NULL.
>
> Fixes: 54ff892b76c6 ("coresight: etm4x: splitting struct etmv4_drvdata")
> Signed-off-by: Yeoreum Yun <yeoreum.yun at arm.com>
> ---
> drivers/hwtracing/coresight/coresight-config.c | 18 ++--
> drivers/hwtracing/coresight/coresight-config.h | 22 ++++
> drivers/hwtracing/coresight/coresight-etm4x-cfg.c | 13 ++-
> drivers/hwtracing/coresight/coresight-etm4x-core.c | 118 ++++++++++++---------
> .../hwtracing/coresight/coresight-etm4x-sysfs.c | 6 +-
> drivers/hwtracing/coresight/coresight-etm4x.h | 4 +-
> 6 files changed, 113 insertions(+), 68 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-config.c b/drivers/hwtracing/coresight/coresight-config.c
> index 4f72ae71b696e..0e296289f286d 100644
> --- a/drivers/hwtracing/coresight/coresight-config.c
> +++ b/drivers/hwtracing/coresight/coresight-config.c
> @@ -73,13 +73,12 @@ static void cscfg_init_reg_param(struct cscfg_feature_csdev *feat_csdev,
> /* set values into the driver locations referenced in cscfg_reg_csdev */
> static int cscfg_set_on_enable(struct cscfg_feature_csdev *feat_csdev)
> {
> - unsigned long flags;
> int i;
>
> - raw_spin_lock_irqsave(feat_csdev->drv_spinlock, flags);
> - for (i = 0; i < feat_csdev->nr_regs; i++)
> - cscfg_set_reg(&feat_csdev->regs_csdev[i]);
> - raw_spin_unlock_irqrestore(feat_csdev->drv_spinlock, flags);
> + scoped_guard(feat_csdev_lock, feat_csdev) {
> + for (i = 0; i < feat_csdev->nr_regs; i++)
> + cscfg_set_reg(&feat_csdev->regs_csdev[i]);
> + }
> dev_dbg(&feat_csdev->csdev->dev, "Feature %s: %s",
> feat_csdev->feat_desc->name, "set on enable");
> return 0;
> @@ -88,13 +87,12 @@ static int cscfg_set_on_enable(struct cscfg_feature_csdev *feat_csdev)
> /* copy back values from the driver locations referenced in cscfg_reg_csdev */
> static void cscfg_save_on_disable(struct cscfg_feature_csdev *feat_csdev)
> {
> - unsigned long flags;
> int i;
>
> - raw_spin_lock_irqsave(feat_csdev->drv_spinlock, flags);
> - for (i = 0; i < feat_csdev->nr_regs; i++)
> - cscfg_save_reg(&feat_csdev->regs_csdev[i]);
> - raw_spin_unlock_irqrestore(feat_csdev->drv_spinlock, flags);
> + scoped_guard(feat_csdev_lock, feat_csdev) {
> + for (i = 0; i < feat_csdev->nr_regs; i++)
> + cscfg_save_reg(&feat_csdev->regs_csdev[i]);
> + }
> dev_dbg(&feat_csdev->csdev->dev, "Feature %s: %s",
> feat_csdev->feat_desc->name, "save on disable");
> }
> diff --git a/drivers/hwtracing/coresight/coresight-config.h b/drivers/hwtracing/coresight/coresight-config.h
> index 90fd937d3bd83..ae6295e308131 100644
> --- a/drivers/hwtracing/coresight/coresight-config.h
> +++ b/drivers/hwtracing/coresight/coresight-config.h
> @@ -7,6 +7,7 @@
> #ifndef _CORESIGHT_CORESIGHT_CONFIG_H
> #define _CORESIGHT_CORESIGHT_CONFIG_H
>
> +#include <linux/cleanup.h>
> #include <linux/coresight.h>
> #include <linux/types.h>
>
> @@ -259,4 +260,25 @@ void cscfg_csdev_disable_config(struct cscfg_config_csdev *config_csdev);
> /* reset a feature to default values */
> void cscfg_reset_feat(struct cscfg_feature_csdev *feat_csdev);
>
> +#define feat_csdev_lock(feat_csdev, flags) \
> + do { \
> + raw_spinlock_t *__lock = feat_csdev->drv_spinlock; \
> + typecheck(unsigned long, flags); \
> + if (__lock) \
> + raw_spin_lock_irqsave(__lock, flags); \
> + } while (0)
> +
> +#define feat_csdev_unlock(feat_csdev, flags) \
> + do { \
> + raw_spinlock_t *__lock = feat_csdev->drv_spinlock; \
> + typecheck(unsigned long, flags); \
> + if (__lock) \
> + raw_spin_unlock_irqrestore(__lock, flags); \
> + } while (0)
> +
> +DEFINE_LOCK_GUARD_1(feat_csdev_lock, struct cscfg_feature_csdev,
> + feat_csdev_lock(_T->lock, _T->flags),
> + feat_csdev_unlock(_T->lock, _T->flags),
> + unsigned long flags)
> +
> #endif /* _CORESIGHT_CORESIGHT_CONFIG_H */
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> index e1a59b4345052..d24f533c623d0 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;
>
> if (((offset >= TRCEVENTCTL0R) && (offset <= TRCVIPCSSCTLR)) ||
> @@ -154,11 +154,14 @@ static int etm4_cfg_load_feature(struct coresight_device *csdev,
> int i = 0, err = 0;
>
> /*
> - * essential we set the device spinlock - this is used in the generic
> - * programming routines when copying values into the drvdata structures
> - * via the pointers setup in etm4_cfg_map_reg_offset().
> + * drvdata structure of etm4 for configfs is active_config and
> + * this active_config is protected with csdev->mode by restricting
> + * access to active_config after mode changed to PERF or SYSFS.
> + *
> + * Therefore, it doesn't need to protected with etmv4_drvdata->spinlock
> + * to feature applying and set the NULL.
> */
> - feat_csdev->drv_spinlock = &drvdata->spinlock;
> + feat_csdev->drv_spinlock = NULL;
>
> /* process the register descriptions */
> for (i = 0; i < feat_csdev->nr_regs && !err; i++) {
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index 2247ad55d4442..2df7f592bb5cf 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -239,6 +239,7 @@ void etm4_release_trace_id(struct etmv4_drvdata *drvdata)
> struct etm4_enable_arg {
> struct etmv4_drvdata *drvdata;
> struct coresight_path *path;
> + struct etmv4_config config;
drvdata contains both active_config and config - why the extra copy here?
> int rc;
> };
>
> @@ -264,10 +265,11 @@ static void etm4x_prohibit_trace(struct etmv4_drvdata *drvdata)
> static u64 etm4x_get_kern_user_filter(struct etmv4_drvdata *drvdata)
> {
> u64 trfcr = drvdata->trfcr;
> + struct etmv4_config *config = &drvdata->active_config;
>
> - if (drvdata->config.mode & ETM_MODE_EXCL_KERN)
> + if (config->mode & ETM_MODE_EXCL_KERN)
> trfcr &= ~TRFCR_EL1_ExTRE;
> - if (drvdata->config.mode & ETM_MODE_EXCL_USER)
> + if (config->mode & ETM_MODE_EXCL_USER)
> trfcr &= ~TRFCR_EL1_E0TRE;
>
> return trfcr;
> @@ -275,7 +277,7 @@ static u64 etm4x_get_kern_user_filter(struct etmv4_drvdata *drvdata)
>
> /*
> * etm4x_allow_trace - Allow CPU tracing in the respective ELs,
> - * as configured by the drvdata->config.mode for the current
> + * as configured by the drvdata->active_config.mode for the current
> * session. Even though we have TRCVICTLR bits to filter the
> * trace in the ELs, it doesn't prevent the ETM from generating
> * a packet (e.g, TraceInfo) that might contain the addresses from
> @@ -286,12 +288,13 @@ static u64 etm4x_get_kern_user_filter(struct etmv4_drvdata *drvdata)
> static void etm4x_allow_trace(struct etmv4_drvdata *drvdata)
> {
> u64 trfcr, guest_trfcr;
> + struct etmv4_config *config = &drvdata->active_config;
>
> /* If the CPU doesn't support FEAT_TRF, nothing to do */
> if (!drvdata->trfcr)
> return;
>
> - if (drvdata->config.mode & ETM_MODE_EXCL_HOST)
> + if (config->mode & ETM_MODE_EXCL_HOST)
> trfcr = drvdata->trfcr & ~(TRFCR_EL1_ExTRE | TRFCR_EL1_E0TRE);
> else
> trfcr = etm4x_get_kern_user_filter(drvdata);
> @@ -299,7 +302,7 @@ static void etm4x_allow_trace(struct etmv4_drvdata *drvdata)
> write_trfcr(trfcr);
>
> /* Set filters for guests and pass to KVM */
> - if (drvdata->config.mode & ETM_MODE_EXCL_GUEST)
> + if (config->mode & ETM_MODE_EXCL_GUEST)
> guest_trfcr = drvdata->trfcr & ~(TRFCR_EL1_ExTRE | TRFCR_EL1_E0TRE);
> else
> guest_trfcr = etm4x_get_kern_user_filter(drvdata);
> @@ -492,7 +495,7 @@ static int etm4_enable_trace_unit(struct etmv4_drvdata *drvdata)
> static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
> {
> int i, rc;
> - struct etmv4_config *config = &drvdata->config;
> + struct etmv4_config *config = &drvdata->active_config;
> struct coresight_device *csdev = drvdata->csdev;
> struct device *etm_dev = &csdev->dev;
> struct csdev_access *csa = &csdev->access;
> @@ -612,27 +615,44 @@ 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;
> - if (!coresight_take_mode(csdev, CS_MODE_SYSFS)) {
> - /* Someone is already using the tracer */
> - arg->rc = -EBUSY;
> - return;
> + drvdata = arg->drvdata;
> + csdev = drvdata->csdev;
> +
> + drvdata->active_config = arg->config;
This can happen before the smp call removing the need for arg->config?
> +
> + /* 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)
> + return;
> }
>
> - arg->rc = etm4_enable_hw(arg->drvdata);
> + drvdata->trcid = arg->path->trace_id;
>
> - /* The tracer didn't start */
> + /* 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);
> + cscfg_csdev_disable_active_config(csdev);
> return;
> }
>
> + drvdata->sticky_enable = true;
> csdev->path = arg->path;
> +
> + return;
> }
>
> /*
> @@ -669,7 +689,7 @@ static int etm4_config_timestamp_event(struct etmv4_drvdata *drvdata,
> {
> int ctridx;
> int rselector;
> - 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 (!drvdata->nr_cntr)
> @@ -752,7 +772,7 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
> {
> int ret = 0;
> struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> - 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,
> };
> @@ -919,46 +939,36 @@ static int etm4_enable_sysfs(struct coresight_device *csdev, struct coresight_pa
> {
> struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> struct etm4_enable_arg arg = { };
> - unsigned long cfg_hash;
> - int ret, preset;
> + int ret;
>
> - /* 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;
> - }
> + if (!coresight_take_mode(csdev, CS_MODE_SYSFS)) {
> + /* Someone is already using the tracer */
> + return -EBUSY;
> }
>
> - 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.path = path;
> +
> + scoped_guard(raw_spinlock, &drvdata->spinlock) {
> + arg.config = drvdata->config;
Given as mentioned above that once a mode is set then active_config is
protected, this should simply be drvdata->active_config =
drvdata->config; ??
> + }
> +
> 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)
> + if (!ret) {
> + dev_dbg(&csdev->dev, "ETM tracing enabled\n");
> + } else {
> etm4_release_trace_id(drvdata);
> + /* The tracer didn't start */
> + coresight_set_mode(csdev, CS_MODE_DISABLED);
> + }
>
> - raw_spin_unlock(&drvdata->spinlock);
> -
> - if (!ret)
> - dev_dbg(&csdev->dev, "ETM tracing enabled\n");
> return ret;
> }
>
> @@ -1044,7 +1054,7 @@ static void etm4_disable_trace_unit(struct etmv4_drvdata *drvdata)
> static void etm4_disable_hw(struct etmv4_drvdata *drvdata)
> {
> u32 control;
> - 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;
> @@ -1086,8 +1096,9 @@ static void etm4_disable_sysfs_smp_call(void *info)
>
> etm4_disable_hw(drvdata);
>
> + cscfg_csdev_disable_active_config(drvdata->csdev);
> +
> drvdata->csdev->path = NULL;
> - coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED);
> }
>
> static int etm4_disable_perf(struct coresight_device *csdev,
> @@ -1130,8 +1141,9 @@ static int etm4_disable_perf(struct coresight_device *csdev,
> static void etm4_disable_sysfs(struct coresight_device *csdev)
> {
> struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> -
> - raw_spin_lock(&drvdata->spinlock);
> + struct etmv4_config *config = &drvdata->config;
> + const struct etmv4_config *active_config = &drvdata->active_config;
> + int i;
>
> /*
> * Executing etm4_disable_hw on the cpu whose ETM is being disabled
> @@ -1140,9 +1152,17 @@ 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);
> + /*
> + * Userspace may read ss_status and cntr_val through sysfs after
> + * the sysfs-session has been disabled.
> + */
> + for (i = 0; i < drvdata->nr_ss_cmp; i++)
> + config->ss_status[i] = active_config->ss_status[i];
>
> - cscfg_csdev_disable_active_config(csdev);
> + for (i = 0; i < drvdata->nr_cntr; i++)
> + config->cntr_val[i] = active_config->cntr_val[i];
> +
Readback of TRCSEQSTR needed here too.
> + coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED);
>
> /*
> * we only release trace IDs when resetting sysfs.
> @@ -1690,7 +1710,7 @@ 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
> @@ -1731,7 +1751,7 @@ 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)
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> index 8d73248b840a6..f64c0acebc701 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> @@ -1613,7 +1613,7 @@ static ssize_t cntr_val_store(struct device *dev,
> return -EINVAL;
> if (val > ETM_CNTR_MAX_VAL)
> return -EINVAL;
> - if (coresight_get_mode(drvdata->csdev))
> + if (coresight_get_mode(drvdata->csdev) == CS_MODE_SYSFS)
> return -EBUSY;
>
> raw_spin_lock(&drvdata->spinlock);
> @@ -1799,7 +1799,7 @@ static ssize_t sshot_ctrl_store(struct device *dev,
>
> if (kstrtoul(buf, 16, &val))
> return -EINVAL;
> - if (coresight_get_mode(drvdata->csdev))
> + if (coresight_get_mode(drvdata->csdev) == CS_MODE_SYSFS)
> return -EBUSY;
>
> raw_spin_lock(&drvdata->spinlock);
> @@ -1851,7 +1851,7 @@ static ssize_t sshot_pe_ctrl_store(struct device *dev,
>
> if (kstrtoul(buf, 16, &val))
> return -EINVAL;
> - if (coresight_get_mode(drvdata->csdev))
> + if (coresight_get_mode(drvdata->csdev) == CS_MODE_SYSFS)
> return -EBUSY;
>
> raw_spin_lock(&drvdata->spinlock);
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> index df9e0748d71ec..c33700711154d 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> @@ -1019,7 +1019,8 @@ 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.
> - * @config: structure holding configuration parameters.
> + * @active_config: structure holding current applied configuration.
> + * @config: structure holding sysfs mode configuration.
> * @save_state: State to be preserved across power loss
> * @skip_power_up: Indicates if an implementation can skip powering up
> * the trace unit.
> @@ -1077,6 +1078,7 @@ struct etmv4_drvdata {
> bool skip_power_up : 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);
>
Regards
Mike
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