From: James Clark <james.clark@linaro.org>
To: Suzuki K Poulose <suzuki.poulose@arm.com>,
Mike Leach <mike.leach@arm.com>, Leo Yan <leo.yan@arm.com>,
Suyash Mahar <smahar@meta.com>,
Yeoreum Yun <yeoreum.yun@arm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Qi Liu <liuqi115@huawei.com>, Junhao He <hejunhao3@huawei.com>,
coresight@lists.linaro.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
James Clark <james.clark@linaro.org>,
Jonathan Cameron <jic23@kernel.org>
Subject: [PATCH v3 5/8] coresight: tmc-etr: Use session ID for buffer ownership
Date: Tue, 28 Jul 2026 16:00:17 +0100 [thread overview]
Message-ID: <20260728-james-cs-multiple-per-threads-v3-5-6aee7579f1dc@linaro.org> (raw)
In-Reply-To: <20260728-james-cs-multiple-per-threads-v3-0-6aee7579f1dc@linaro.org>
Comparing numeric PIDs for ownership no longer matches the sharing rules
in coresight_sink_can_share(), change it to compare the session identity
instead.
Now that we're not using a numeric PID for ownership we can't use the
IDR map. Change it to a simple linear realloc'd array, it's unlikely the
performance difference is measurable, systems wouldn't have more than a
handful of shared sources for one sink, and this is only accessed once
at setup.
Assisted-by: Codex:GPT-5.6-Sol
Fixes: 8d03cfd16a72 ("coresight: tmc-etr: Add support for CPU-wide trace scenarios")
Signed-off-by: James Clark <james.clark@linaro.org>
---
drivers/hwtracing/coresight/coresight-etb10.c | 3 +-
drivers/hwtracing/coresight/coresight-etm-perf.c | 4 +-
drivers/hwtracing/coresight/coresight-tmc-core.c | 4 +-
drivers/hwtracing/coresight/coresight-tmc-etf.c | 5 +-
drivers/hwtracing/coresight/coresight-tmc-etr.c | 139 ++++++++++++-----------
drivers/hwtracing/coresight/coresight-tmc.h | 16 ++-
drivers/hwtracing/coresight/coresight-trbe.c | 3 +-
drivers/hwtracing/coresight/ultrasoc-smb.c | 3 +-
include/linux/coresight.h | 4 +-
9 files changed, 100 insertions(+), 81 deletions(-)
diff --git a/drivers/hwtracing/coresight/coresight-etb10.c b/drivers/hwtracing/coresight/coresight-etb10.c
index a827f76b8144..6a4a1edf46ba 100644
--- a/drivers/hwtracing/coresight/coresight-etb10.c
+++ b/drivers/hwtracing/coresight/coresight-etb10.c
@@ -371,7 +371,8 @@ static int etb_disable(struct coresight_device *csdev)
}
static void *etb_alloc_buffer(struct coresight_device *csdev,
- struct perf_event *event, void **pages,
+ struct perf_event *event,
+ struct etm_session_id *owner, void **pages,
int nr_pages, bool overwrite)
{
int node;
diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
index 28cf319a39da..652beee2edbd 100644
--- a/drivers/hwtracing/coresight/coresight-etm-perf.c
+++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
@@ -517,7 +517,9 @@ static void *etm_setup_aux(struct perf_event *event, void **pages,
* sinks.
*/
event_data->snk_config =
- sink_ops(sink)->alloc_buffer(sink, event, pages,
+ sink_ops(sink)->alloc_buffer(sink, event,
+ &event_data->session_id,
+ pages,
nr_pages, overwrite);
if (!event_data->snk_config)
goto err;
diff --git a/drivers/hwtracing/coresight/coresight-tmc-core.c b/drivers/hwtracing/coresight/coresight-tmc-core.c
index c89fe996af23..873868718b14 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-core.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-core.c
@@ -9,7 +9,6 @@
#include <linux/init.h>
#include <linux/types.h>
#include <linux/device.h>
-#include <linux/idr.h>
#include <linux/io.h>
#include <linux/iommu.h>
#include <linux/err.h>
@@ -832,8 +831,7 @@ static int __tmc_probe(struct device *dev, struct resource *res)
ret = tmc_etr_setup_caps(dev, devid, &desc.access);
if (ret)
goto out;
- idr_init(&drvdata->idr);
- mutex_init(&drvdata->idr_mutex);
+ mutex_init(&drvdata->perf_bufs_mutex);
dev_list = "tmc_etr";
break;
case TMC_CONFIG_TYPE_ETF:
diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
index 3836063031d7..d90090b846ab 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
@@ -419,8 +419,9 @@ static void tmc_disable_etf_link(struct coresight_device *csdev,
}
static void *tmc_alloc_etf_buffer(struct coresight_device *csdev,
- struct perf_event *event, void **pages,
- int nr_pages, bool overwrite)
+ struct perf_event *event,
+ struct etm_session_id *owner,
+ void **pages, int nr_pages, bool overwrite)
{
int node;
struct cs_buffers *buf;
diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
index be5ed04a554f..324d94e6d7e1 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
@@ -8,7 +8,6 @@
#include <linux/coresight.h>
#include <linux/dma-mapping.h>
#include <linux/iommu.h>
-#include <linux/idr.h>
#include <linux/mutex.h>
#include <linux/refcount.h>
#include <linux/slab.h>
@@ -37,8 +36,6 @@ struct etr_buf_hw {
* etr_perf_buffer - Perf buffer used for ETR
* @drvdata - The ETR drvdaga this buffer has been allocated for.
* @etr_buf - Actual buffer used by the ETR
- * @pid - The PID of the session owner that etr_perf_buffer
- * belongs to.
* @snaphost - Perf session mode
* @nr_pages - Number of pages in the ring buffer.
* @pages - Array of Pages in the ring buffer.
@@ -46,7 +43,6 @@ struct etr_buf_hw {
struct etr_perf_buffer {
struct tmc_drvdata *drvdata;
struct etr_buf *etr_buf;
- pid_t pid;
bool snapshot;
int nr_pages;
void **pages;
@@ -1396,16 +1392,16 @@ alloc_etr_buf(struct tmc_drvdata *drvdata, struct perf_event *event,
return ERR_PTR(-ENOMEM);
}
-static struct etr_buf *
-get_perf_etr_buf_cpu_wide(struct tmc_drvdata *drvdata,
- struct perf_event *event, int nr_pages,
- void **pages, bool snapshot)
+static struct etr_buf *get_perf_etr_buf_cpu_wide(struct tmc_drvdata *drvdata,
+ struct perf_event *event,
+ struct etm_session_id *owner,
+ int nr_pages, void **pages,
+ bool snapshot)
{
- int ret;
- pid_t pid = task_pid_nr(event->owner);
- struct etr_buf *etr_buf;
+ struct etr_buf_mapping *perf_bufs;
+ struct etr_buf *etr_buf, *existing;
+ unsigned int i;
-retry:
/*
* An etr_perf_buffer is associated with an event and holds a reference
* to the AUX ring buffer that was created for that event. In CPU-wide
@@ -1424,69 +1420,75 @@ get_perf_etr_buf_cpu_wide(struct tmc_drvdata *drvdata,
* allocated for this session. If so it is shared with this event,
* otherwise it is created.
*/
- mutex_lock(&drvdata->idr_mutex);
- etr_buf = idr_find(&drvdata->idr, pid);
- if (etr_buf) {
- refcount_inc(&etr_buf->refcount);
- mutex_unlock(&drvdata->idr_mutex);
- return etr_buf;
+ mutex_lock(&drvdata->perf_bufs_mutex);
+ for (i = 0; i < drvdata->nr_perf_bufs; i++) {
+ if (etm_perf_compare_session(&drvdata->perf_bufs[i].owner, owner)) {
+ etr_buf = drvdata->perf_bufs[i].buf;
+ refcount_inc(&etr_buf->refcount);
+ mutex_unlock(&drvdata->perf_bufs_mutex);
+ return etr_buf;
+ }
}
/* If we made it here no buffer has been allocated, do so now. */
- mutex_unlock(&drvdata->idr_mutex);
+ mutex_unlock(&drvdata->perf_bufs_mutex);
etr_buf = alloc_etr_buf(drvdata, event, nr_pages, pages, snapshot);
if (IS_ERR(etr_buf))
return etr_buf;
- /* Now that we have a buffer, add it to the IDR. */
- mutex_lock(&drvdata->idr_mutex);
- ret = idr_alloc(&drvdata->idr, etr_buf, pid, pid + 1, GFP_KERNEL);
- mutex_unlock(&drvdata->idr_mutex);
-
- /* Another event with this session ID has allocated this buffer. */
- if (ret == -ENOSPC) {
- tmc_free_etr_buf(etr_buf);
- goto retry;
+ mutex_lock(&drvdata->perf_bufs_mutex);
+ for (i = 0; i < drvdata->nr_perf_bufs; i++) {
+ if (etm_perf_compare_session(&drvdata->perf_bufs[i].owner, owner)) {
+ existing = drvdata->perf_bufs[i].buf;
+ refcount_inc(&existing->refcount);
+ mutex_unlock(&drvdata->perf_bufs_mutex);
+ tmc_free_etr_buf(etr_buf);
+ return existing;
+ }
}
- /* The IDR can't allocate room for a new session, abandon ship. */
- if (ret == -ENOMEM) {
+ perf_bufs = krealloc_array(drvdata->perf_bufs,
+ drvdata->nr_perf_bufs + 1,
+ sizeof(*perf_bufs), GFP_KERNEL);
+ if (!perf_bufs) {
+ mutex_unlock(&drvdata->perf_bufs_mutex);
tmc_free_etr_buf(etr_buf);
- return ERR_PTR(ret);
+ return ERR_PTR(-ENOMEM);
}
+ drvdata->perf_bufs = perf_bufs;
+ perf_bufs[drvdata->nr_perf_bufs].owner = *owner;
+ perf_bufs[drvdata->nr_perf_bufs].buf = etr_buf;
+ drvdata->nr_perf_bufs++;
+ mutex_unlock(&drvdata->perf_bufs_mutex);
return etr_buf;
}
-static struct etr_buf *
-get_perf_etr_buf_per_thread(struct tmc_drvdata *drvdata,
- struct perf_event *event, int nr_pages,
- void **pages, bool snapshot)
+static struct etr_buf *get_perf_etr_buf(struct tmc_drvdata *drvdata,
+ struct perf_event *event,
+ struct etm_session_id *owner,
+ int nr_pages, void **pages,
+ bool snapshot)
{
/*
- * In per-thread mode the etr_buf isn't shared, so just go ahead
- * with memory allocation.
+ * Events without a CPU must have inherit=false so always target a
+ * single process. etm_perf_sink_can_share() prevents other single
+ * process events from sharing sinks, so take a shortcut and go ahead
+ * with memory allocation without using shared drvdata->perf_bufs.
*/
- return alloc_etr_buf(drvdata, event, nr_pages, pages, snapshot);
-}
-
-static struct etr_buf *
-get_perf_etr_buf(struct tmc_drvdata *drvdata, struct perf_event *event,
- int nr_pages, void **pages, bool snapshot)
-{
if (event->cpu == -1)
- return get_perf_etr_buf_per_thread(drvdata, event, nr_pages,
- pages, snapshot);
+ return alloc_etr_buf(drvdata, event, nr_pages, pages, snapshot);
- return get_perf_etr_buf_cpu_wide(drvdata, event, nr_pages,
+ return get_perf_etr_buf_cpu_wide(drvdata, event, owner, nr_pages,
pages, snapshot);
}
static struct etr_perf_buffer *
tmc_etr_setup_perf_buf(struct tmc_drvdata *drvdata, struct perf_event *event,
- int nr_pages, void **pages, bool snapshot)
+ struct etm_session_id *owner, int nr_pages, void **pages,
+ bool snapshot)
{
int node;
struct etr_buf *etr_buf;
@@ -1498,7 +1500,8 @@ tmc_etr_setup_perf_buf(struct tmc_drvdata *drvdata, struct perf_event *event,
if (!etr_perf)
return ERR_PTR(-ENOMEM);
- etr_buf = get_perf_etr_buf(drvdata, event, nr_pages, pages, snapshot);
+ etr_buf = get_perf_etr_buf(drvdata, event, owner, nr_pages, pages,
+ snapshot);
if (!IS_ERR(etr_buf))
goto done;
@@ -1508,7 +1511,7 @@ tmc_etr_setup_perf_buf(struct tmc_drvdata *drvdata, struct perf_event *event,
done:
/*
* Keep a reference to the ETR this buffer has been allocated for
- * in order to have access to the IDR in tmc_free_etr_buffer().
+ * in order to have access to the buffer array in tmc_free_etr_buffer().
*/
etr_perf->drvdata = drvdata;
etr_perf->etr_buf = etr_buf;
@@ -1516,22 +1519,21 @@ tmc_etr_setup_perf_buf(struct tmc_drvdata *drvdata, struct perf_event *event,
return etr_perf;
}
-
static void *tmc_alloc_etr_buffer(struct coresight_device *csdev,
- struct perf_event *event, void **pages,
+ struct perf_event *event,
+ struct etm_session_id *owner, void **pages,
int nr_pages, bool snapshot)
{
struct etr_perf_buffer *etr_perf;
struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
- etr_perf = tmc_etr_setup_perf_buf(drvdata, event,
+ etr_perf = tmc_etr_setup_perf_buf(drvdata, event, owner,
nr_pages, pages, snapshot);
if (IS_ERR(etr_perf)) {
dev_dbg(&csdev->dev, "Unable to allocate ETR buffer\n");
return NULL;
}
- etr_perf->pid = task_pid_nr(event->owner);
etr_perf->snapshot = snapshot;
etr_perf->nr_pages = nr_pages;
etr_perf->pages = pages;
@@ -1543,28 +1545,33 @@ static void tmc_free_etr_buffer(void *config)
{
struct etr_perf_buffer *etr_perf = config;
struct tmc_drvdata *drvdata = etr_perf->drvdata;
- struct etr_buf *buf, *etr_buf = etr_perf->etr_buf;
+ struct etr_buf *etr_buf = etr_perf->etr_buf;
+ unsigned int i;
if (!etr_buf)
goto free_etr_perf_buffer;
- mutex_lock(&drvdata->idr_mutex);
+ mutex_lock(&drvdata->perf_bufs_mutex);
/* If we are not the last one to use the buffer, don't touch it. */
if (!refcount_dec_and_test(&etr_buf->refcount)) {
- mutex_unlock(&drvdata->idr_mutex);
+ mutex_unlock(&drvdata->perf_bufs_mutex);
goto free_etr_perf_buffer;
}
- /* We are the last one, remove from the IDR and free the buffer. */
- buf = idr_remove(&drvdata->idr, etr_perf->pid);
- mutex_unlock(&drvdata->idr_mutex);
+ for (i = 0; i < drvdata->nr_perf_bufs; i++) {
+ if (drvdata->perf_bufs[i].buf != etr_buf)
+ continue;
- /*
- * Something went very wrong if the buffer associated with this ID
- * is not the same in the IDR. Leak to avoid use after free.
- */
- if (buf && WARN_ON(buf != etr_buf))
- goto free_etr_perf_buffer;
+ drvdata->nr_perf_bufs--;
+ drvdata->perf_bufs[i] =
+ drvdata->perf_bufs[drvdata->nr_perf_bufs];
+ if (!drvdata->nr_perf_bufs) {
+ kfree(drvdata->perf_bufs);
+ drvdata->perf_bufs = NULL;
+ }
+ break;
+ }
+ mutex_unlock(&drvdata->perf_bufs_mutex);
tmc_free_etr_buf(etr_perf->etr_buf);
diff --git a/drivers/hwtracing/coresight/coresight-tmc.h b/drivers/hwtracing/coresight/coresight-tmc.h
index 9b153b7910fb..0125f2ad78ed 100644
--- a/drivers/hwtracing/coresight/coresight-tmc.h
+++ b/drivers/hwtracing/coresight/coresight-tmc.h
@@ -8,7 +8,6 @@
#define _CORESIGHT_TMC_H
#include <linux/dma-mapping.h>
-#include <linux/idr.h>
#include <linux/miscdevice.h>
#include <linux/mutex.h>
#include <linux/refcount.h>
@@ -192,6 +191,11 @@ struct etr_buf {
void *private;
};
+struct etr_buf_mapping {
+ struct etm_session_id owner;
+ struct etr_buf *buf;
+};
+
/**
* @paddr : Start address of reserved memory region.
* @vaddr : Corresponding CPU virtual address.
@@ -239,8 +243,9 @@ struct tmc_resrv_buf {
* @etr_caps: Bitmask of capabilities of the TMC ETR, inferred from the
* device configuration register (DEVID)
* @etr_mode: User preferred mode of the ETR device, default auto mode.
- * @idr: Holds etr_bufs allocated for this ETR.
- * @idr_mutex: Access serialisation for idr.
+ * @perf_bufs: CPU-wide Perf buffers and their owners.
+ * @nr_perf_bufs: Number of entries in @perf_bufs.
+ * @perf_bufs_mutex: Access serialisation for @perf_bufs.
* @sysfs_buf: SYSFS buffer for ETR.
* @perf_buf: PERF buffer for ETR.
* @resrv_buf: Used by ETR as hardware trace buffer and for trace data
@@ -274,8 +279,9 @@ struct tmc_drvdata {
u32 trigger_cntr;
u32 etr_caps;
enum etr_mode etr_mode;
- struct idr idr;
- struct mutex idr_mutex;
+ struct etr_buf_mapping *perf_bufs;
+ unsigned int nr_perf_bufs;
+ struct mutex perf_bufs_mutex;
struct etr_buf *sysfs_buf;
struct etr_buf *perf_buf;
struct tmc_resrv_buf resrv_buf;
diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
index c7cbca45f2de..81841dc95e0c 100644
--- a/drivers/hwtracing/coresight/coresight-trbe.c
+++ b/drivers/hwtracing/coresight/coresight-trbe.c
@@ -746,7 +746,8 @@ static unsigned long trbe_get_trace_size(struct perf_output_handle *handle,
}
static void *arm_trbe_alloc_buffer(struct coresight_device *csdev,
- struct perf_event *event, void **pages,
+ struct perf_event *event,
+ struct etm_session_id *owner, void **pages,
int nr_pages, bool snapshot)
{
struct trbe_buf *buf;
diff --git a/drivers/hwtracing/coresight/ultrasoc-smb.c b/drivers/hwtracing/coresight/ultrasoc-smb.c
index 20a950b9dd4f..f66ec53070d7 100644
--- a/drivers/hwtracing/coresight/ultrasoc-smb.c
+++ b/drivers/hwtracing/coresight/ultrasoc-smb.c
@@ -302,7 +302,8 @@ static int smb_disable(struct coresight_device *csdev)
}
static void *smb_alloc_buffer(struct coresight_device *csdev,
- struct perf_event *event, void **pages,
+ struct perf_event *event,
+ struct etm_session_id *owner, void **pages,
int nr_pages, bool overwrite)
{
struct cs_buffers *buf;
diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index 1c06a9800cfe..9e29f2cbf557 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -37,6 +37,7 @@
#define CORESIGHT_UNLOCK 0xc5acce55
extern const struct bus_type coresight_bustype;
+struct etm_session_id;
enum coresight_dev_type {
CORESIGHT_DEV_TYPE_SINK,
@@ -371,7 +372,8 @@ struct coresight_ops_sink {
struct coresight_path *path);
int (*disable)(struct coresight_device *csdev);
void *(*alloc_buffer)(struct coresight_device *csdev,
- struct perf_event *event, void **pages,
+ struct perf_event *event,
+ struct etm_session_id *owner, void **pages,
int nr_pages, bool overwrite);
void (*free_buffer)(void *config);
unsigned long (*update_buffer)(struct coresight_device *csdev,
--
2.34.1
next prev parent reply other threads:[~2026-07-28 15:01 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-28 15:00 [PATCH v3 0/8] coresight: Prevent per-thread events from sharing a sink James Clark
2026-07-28 15:00 ` [PATCH v3 1/8] coresight: tmc-etr: Don't stop Perf cleanup for active sysfs reads James Clark
2026-08-12 16:45 ` Leo Yan
2026-08-13 9:02 ` James Clark
2026-07-28 15:00 ` [PATCH v3 2/8] coresight: configfs: Don't assume active until cscfg_mgr is set James Clark
2026-08-13 9:09 ` Leo Yan
2026-08-13 9:24 ` James Clark
2026-07-28 15:00 ` [PATCH v3 3/8] coresight: etm-perf: Flush workqueue before unloading module James Clark
2026-08-13 14:19 ` Leo Yan
2026-08-14 8:55 ` James Clark
2026-07-28 15:00 ` [PATCH v3 4/8] coresight: tmc-etr: Prevent per-thread events from sharing a sink James Clark
2026-08-13 16:05 ` Leo Yan
2026-08-14 9:09 ` James Clark
2026-08-19 8:45 ` Leo Yan
2026-08-20 11:09 ` James Clark
2026-08-20 11:27 ` James Clark
2026-08-25 17:32 ` Leo Yan
2026-08-26 8:40 ` James Clark
2026-07-28 15:00 ` James Clark [this message]
2026-07-28 15:00 ` [PATCH v3 6/8] coresight: tmc-etf: " James Clark
2026-07-28 15:00 ` [PATCH v3 7/8] coresight: etb10: " James Clark
2026-07-28 15:00 ` [PATCH v3 8/8] coresight: ultrasoc-smb: " James Clark
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