[for-next][PATCH 0/4] tracing: Updates for v6.14

[for-next][PATCH 0/4] tracing: Updates for v6.14

[Steven Rostedt]

  git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
trace/for-next

Head SHA1: 80c3e28528ff9f269937fcfe73895213a2e14905


Masami Hiramatsu (Google) (3):
      tracing/hist: Add poll(POLLIN) support on hist file
      tracing/hist: Support POLLPRI event for poll on histogram
      selftests/tracing: Add hist poll() support test

Steven Rostedt (1):
      tracing: Fix using ret variable in tracing_set_tracer()

----
 include/linux/trace_events.h                       | 14 ++++
 kernel/trace/trace.c                               |  3 +-
 kernel/trace/trace_events.c                        | 14 ++++
 kernel/trace/trace_events_hist.c                   | 93 +++++++++++++++++++++-
 tools/testing/selftests/ftrace/Makefile            |  2 +
 tools/testing/selftests/ftrace/poll.c              | 74 +++++++++++++++++
 .../ftrace/test.d/trigger/trigger-hist-poll.tc     | 74 +++++++++++++++++
 7 files changed, 269 insertions(+), 5 deletions(-)
 create mode 100644 tools/testing/selftests/ftrace/poll.c
 create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc

[for-next][PATCH 1/4] tracing: Fix using ret variable in tracing_set_tracer()

[Steven Rostedt]

From: Steven Rostedt <rostedt@goodmis.org>

When the function tracing_set_tracer() switched over to using the guard()
infrastructure, it did not need to save the 'ret' variable and would just
return the value when an error arised, instead of setting ret and jumping
to an out label.

When CONFIG_TRACER_SNAPSHOT is enabled, it had code that expected the
"ret" variable to be initialized to zero and had set 'ret' while holding
an arch_spin_lock() (not used by guard), and then upon releasing the lock
it would check 'ret' and exit if set. But because ret was only set when an
error occurred while holding the locks, 'ret' would be used uninitialized
if there was no error. The code in the CONFIG_TRACER_SNAPSHOT block should
be self contain. Make sure 'ret' is also set when no error occurred.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/20250106111143.2f90ff65@gandalf.local.home
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202412271654.nJVBuwmF-lkp@intel.com/
Fixes: d33b10c0c73ad ("tracing: Switch trace.c code over to use guard()")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 kernel/trace/trace.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 0aaf442271e9..5aeb898054e7 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6104,8 +6104,7 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
 	if (t->use_max_tr) {
 		local_irq_disable();
 		arch_spin_lock(&tr->max_lock);
-		if (tr->cond_snapshot)
-			ret = -EBUSY;
+		ret = tr->cond_snapshot ? -EBUSY : 0;
 		arch_spin_unlock(&tr->max_lock);
 		local_irq_enable();
 		if (ret)
-- 
2.45.2

[for-next][PATCH 2/4] tracing/hist: Add poll(POLLIN) support on hist file

[Steven Rostedt]

From: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>

Add poll syscall support on the `hist` file. The Waiter will be waken
up when the histogram is updated with POLLIN.

Currently, there is no way to wait for a specific event in userspace.
So user needs to peek the `trace` periodicaly, or wait on `trace_pipe`.
But it is not a good idea to peek at the `trace` for an event that
randomly happens. And `trace_pipe` is not coming back until a page is
filled with events.

This allows a user to wait for a specific event on the `hist` file. User
can set a histogram trigger on the event which they want to monitor
and poll() on its `hist` file. Since this poll() returns POLLIN, the next
poll() will return soon unless a read() happens on that hist file.

NOTE: To read the hist file again, you must set the file offset to 0,
but just for monitoring the event, you may not need to read the
histogram.

Cc: Shuah Khan <shuah@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/173527247756.464571.14236296701625509931.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/trace_events.h     | 14 +++++++
 kernel/trace/trace_events.c      | 14 +++++++
 kernel/trace/trace_events_hist.c | 70 ++++++++++++++++++++++++++++++--
 3 files changed, 95 insertions(+), 3 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 91b8ffbdfa8c..02cde1174487 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -673,6 +673,20 @@ struct trace_event_file {
 	atomic_t		tm_ref;	/* trigger-mode reference counter */
 };
 
+#ifdef CONFIG_HIST_TRIGGERS
+extern struct irq_work hist_poll_work;
+extern wait_queue_head_t hist_poll_wq;
+
+static inline void hist_poll_wakeup(void)
+{
+	if (wq_has_sleeper(&hist_poll_wq))
+		irq_work_queue(&hist_poll_work);
+}
+
+#define hist_poll_wait(file, wait)	\
+	poll_wait(file, &hist_poll_wq, wait)
+#endif
+
 #define __TRACE_EVENT_FLAGS(name, value)				\
 	static int __init trace_init_flags_##name(void)			\
 	{								\
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 047d2775184b..2b9222e7bd5a 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -3094,6 +3094,20 @@ static bool event_in_systems(struct trace_event_call *call,
 	return !*p || isspace(*p) || *p == ',';
 }
 
+#ifdef CONFIG_HIST_TRIGGERS
+/*
+ * Wake up waiter on the hist_poll_wq from irq_work because the hist trigger
+ * may happen in any context.
+ */
+static void hist_poll_event_irq_work(struct irq_work *work)
+{
+	wake_up_all(&hist_poll_wq);
+}
+
+DEFINE_IRQ_WORK(hist_poll_work, hist_poll_event_irq_work);
+DECLARE_WAIT_QUEUE_HEAD(hist_poll_wq);
+#endif
+
 static struct trace_event_file *
 trace_create_new_event(struct trace_event_call *call,
 		       struct trace_array *tr)
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 879b58892b9d..af4be28f01e0 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -5311,6 +5311,8 @@ static void event_hist_trigger(struct event_trigger_data *data,
 
 	if (resolve_var_refs(hist_data, key, var_ref_vals, true))
 		hist_trigger_actions(hist_data, elt, buffer, rec, rbe, key, var_ref_vals);
+
+	hist_poll_wakeup();
 }
 
 static void hist_trigger_stacktrace_print(struct seq_file *m,
@@ -5590,15 +5592,36 @@ static void hist_trigger_show(struct seq_file *m,
 		   n_entries, (u64)atomic64_read(&hist_data->map->drops));
 }
 
+struct hist_file_data {
+	struct file *file;
+	u64 last_read;
+};
+
+static u64 get_hist_hit_count(struct trace_event_file *event_file)
+{
+	struct hist_trigger_data *hist_data;
+	struct event_trigger_data *data;
+	u64 ret = 0;
+
+	list_for_each_entry(data, &event_file->triggers, list) {
+		if (data->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+			hist_data = data->private_data;
+			ret += atomic64_read(&hist_data->map->hits);
+		}
+	}
+	return ret;
+}
+
 static int hist_show(struct seq_file *m, void *v)
 {
+	struct hist_file_data *hist_file = m->private;
 	struct event_trigger_data *data;
 	struct trace_event_file *event_file;
 	int n = 0;
 
 	guard(mutex)(&event_mutex);
 
-	event_file = event_file_file(m->private);
+	event_file = event_file_file(hist_file->file);
 	if (unlikely(!event_file))
 		return -ENODEV;
 
@@ -5606,27 +5629,68 @@ static int hist_show(struct seq_file *m, void *v)
 		if (data->cmd_ops->trigger_type == ETT_EVENT_HIST)
 			hist_trigger_show(m, data, n++);
 	}
+	hist_file->last_read = get_hist_hit_count(event_file);
+
 	return 0;
 }
 
+static __poll_t event_hist_poll(struct file *file, struct poll_table_struct *wait)
+{
+	struct trace_event_file *event_file;
+	struct seq_file *m = file->private_data;
+	struct hist_file_data *hist_file = m->private;
+
+	guard(mutex)(&event_mutex);
+
+	event_file = event_file_data(file);
+	if (!event_file)
+		return EPOLLERR;
+
+	hist_poll_wait(file, wait);
+
+	if (hist_file->last_read != get_hist_hit_count(event_file))
+		return EPOLLIN | EPOLLRDNORM;
+
+	return 0;
+}
+
+static int event_hist_release(struct inode *inode, struct file *file)
+{
+	struct seq_file *m = file->private_data;
+	struct hist_file_data *hist_file = m->private;
+
+	kfree(hist_file);
+	return tracing_single_release_file_tr(inode, file);
+}
+
 static int event_hist_open(struct inode *inode, struct file *file)
 {
+	struct hist_file_data *hist_file;
 	int ret;
 
 	ret = tracing_open_file_tr(inode, file);
 	if (ret)
 		return ret;
 
+	hist_file = kzalloc(sizeof(*hist_file), GFP_KERNEL);
+	if (!hist_file)
+		return -ENOMEM;
+	hist_file->file = file;
+
 	/* Clear private_data to avoid warning in single_open() */
 	file->private_data = NULL;
-	return single_open(file, hist_show, file);
+	ret = single_open(file, hist_show, hist_file);
+	if (ret)
+		kfree(hist_file);
+	return ret;
 }
 
 const struct file_operations event_hist_fops = {
 	.open = event_hist_open,
 	.read = seq_read,
 	.llseek = seq_lseek,
-	.release = tracing_single_release_file_tr,
+	.release = event_hist_release,
+	.poll = event_hist_poll,
 };
 
 #ifdef CONFIG_HIST_TRIGGERS_DEBUG
-- 
2.45.2

[for-next][PATCH 3/4] tracing/hist: Support POLLPRI event for poll on histogram

[Steven Rostedt]

From: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>

Since POLLIN will not be flushed until the hist file is read, the user
needs to repeatedly read() and poll() on the hist file for monitoring the
event continuously. But the read() is somewhat redundant when the user is
only monitoring for event updates.

Add POLLPRI poll event on the hist file so the event returns when a
histogram is updated after open(), poll() or read(). Thus it is possible
to wait for the next event without having to issue a read().

Cc: Shuah Khan <shuah@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/173527248770.464571.2536902137325258133.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace_events_hist.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index af4be28f01e0..261163b00137 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -5595,6 +5595,7 @@ static void hist_trigger_show(struct seq_file *m,
 struct hist_file_data {
 	struct file *file;
 	u64 last_read;
+	u64 last_act;
 };
 
 static u64 get_hist_hit_count(struct trace_event_file *event_file)
@@ -5630,6 +5631,11 @@ static int hist_show(struct seq_file *m, void *v)
 			hist_trigger_show(m, data, n++);
 	}
 	hist_file->last_read = get_hist_hit_count(event_file);
+	/*
+	 * Update last_act too so that poll()/POLLPRI can wait for the next
+	 * event after any syscall on hist file.
+	 */
+	hist_file->last_act = hist_file->last_read;
 
 	return 0;
 }
@@ -5639,6 +5645,8 @@ static __poll_t event_hist_poll(struct file *file, struct poll_table_struct *wai
 	struct trace_event_file *event_file;
 	struct seq_file *m = file->private_data;
 	struct hist_file_data *hist_file = m->private;
+	__poll_t ret = 0;
+	u64 cnt;
 
 	guard(mutex)(&event_mutex);
 
@@ -5648,10 +5656,15 @@ static __poll_t event_hist_poll(struct file *file, struct poll_table_struct *wai
 
 	hist_poll_wait(file, wait);
 
-	if (hist_file->last_read != get_hist_hit_count(event_file))
-		return EPOLLIN | EPOLLRDNORM;
+	cnt = get_hist_hit_count(event_file);
+	if (hist_file->last_read != cnt)
+		ret |= EPOLLIN | EPOLLRDNORM;
+	if (hist_file->last_act != cnt) {
+		hist_file->last_act = cnt;
+		ret |= EPOLLPRI;
+	}
 
-	return 0;
+	return ret;
 }
 
 static int event_hist_release(struct inode *inode, struct file *file)
@@ -5665,6 +5678,7 @@ static int event_hist_release(struct inode *inode, struct file *file)
 
 static int event_hist_open(struct inode *inode, struct file *file)
 {
+	struct trace_event_file *event_file;
 	struct hist_file_data *hist_file;
 	int ret;
 
@@ -5672,16 +5686,25 @@ static int event_hist_open(struct inode *inode, struct file *file)
 	if (ret)
 		return ret;
 
+	guard(mutex)(&event_mutex);
+
+	event_file = event_file_data(file);
+	if (!event_file)
+		return -ENODEV;
+
 	hist_file = kzalloc(sizeof(*hist_file), GFP_KERNEL);
 	if (!hist_file)
 		return -ENOMEM;
+
 	hist_file->file = file;
+	hist_file->last_act = get_hist_hit_count(event_file);
 
 	/* Clear private_data to avoid warning in single_open() */
 	file->private_data = NULL;
 	ret = single_open(file, hist_show, hist_file);
 	if (ret)
 		kfree(hist_file);
+
 	return ret;
 }
 
-- 
2.45.2

[for-next][PATCH 4/4] selftests/tracing: Add hist poll() support test

[Steven Rostedt]

From: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>

Add a testcase for poll() on hist file. This introduces a helper binary
to the ftracetest, because there is no good way to reliably execute
poll() on hist file.

Cc: Shuah Khan <shuah@kernel.org>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/173547867935.569911.10127126796879854182.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 tools/testing/selftests/ftrace/Makefile       |  2 +
 tools/testing/selftests/ftrace/poll.c         | 74 +++++++++++++++++++
 .../test.d/trigger/trigger-hist-poll.tc       | 74 +++++++++++++++++++
 3 files changed, 150 insertions(+)
 create mode 100644 tools/testing/selftests/ftrace/poll.c
 create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc

diff --git a/tools/testing/selftests/ftrace/Makefile b/tools/testing/selftests/ftrace/Makefile
index a1e955d2de4c..49d96bb16355 100644
--- a/tools/testing/selftests/ftrace/Makefile
+++ b/tools/testing/selftests/ftrace/Makefile
@@ -6,4 +6,6 @@ TEST_PROGS := ftracetest-ktap
 TEST_FILES := test.d settings
 EXTRA_CLEAN := $(OUTPUT)/logs/*
 
+TEST_GEN_PROGS = poll
+
 include ../lib.mk
diff --git a/tools/testing/selftests/ftrace/poll.c b/tools/testing/selftests/ftrace/poll.c
new file mode 100644
index 000000000000..53258f7515e7
--- /dev/null
+++ b/tools/testing/selftests/ftrace/poll.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Simple poll on a file.
+ *
+ * Copyright (c) 2024 Google LLC.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define BUFSIZE 4096
+
+/*
+ * Usage:
+ *  poll [-I|-P] [-t timeout] FILE
+ */
+int main(int argc, char *argv[])
+{
+	struct pollfd pfd = {.events = POLLIN};
+	char buf[BUFSIZE];
+	int timeout = -1;
+	int ret, opt;
+
+	while ((opt = getopt(argc, argv, "IPt:")) != -1) {
+		switch (opt) {
+		case 'I':
+			pfd.events = POLLIN;
+			break;
+		case 'P':
+			pfd.events = POLLPRI;
+			break;
+		case 't':
+			timeout = atoi(optarg);
+			break;
+		default:
+			fprintf(stderr, "Usage: %s [-I|-P] [-t timeout] FILE\n",
+				argv[0]);
+			return -1;
+		}
+	}
+	if (optind >= argc) {
+		fprintf(stderr, "Error: Polling file is not specified\n");
+		return -1;
+	}
+
+	pfd.fd = open(argv[optind], O_RDONLY);
+	if (pfd.fd < 0) {
+		fprintf(stderr, "failed to open %s", argv[optind]);
+		perror("open");
+		return -1;
+	}
+
+	/* Reset poll by read if POLLIN is specified. */
+	if (pfd.events & POLLIN)
+		do {} while (read(pfd.fd, buf, BUFSIZE) == BUFSIZE);
+
+	ret = poll(&pfd, 1, timeout);
+	if (ret < 0 && errno != EINTR) {
+		perror("poll");
+		return -1;
+	}
+	close(pfd.fd);
+
+	/* If timeout happned (ret == 0), exit code is 1 */
+	if (ret == 0)
+		return 1;
+
+	return 0;
+}
diff --git a/tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc b/tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc
new file mode 100644
index 000000000000..8d275e3238d9
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc
@@ -0,0 +1,74 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: event trigger - test poll wait on histogram
+# requires: set_event events/sched/sched_process_free/trigger events/sched/sched_process_free/hist
+# flags: instance
+
+POLL=${FTRACETEST_ROOT}/poll
+
+if [ ! -x ${POLL} ]; then
+  echo "poll program is not compiled!"
+  exit_unresolved
+fi
+
+EVENT=events/sched/sched_process_free/
+
+# Check poll ops is supported. Before implementing poll on hist file, it
+# returns soon with POLLIN | POLLOUT, but not POLLPRI.
+
+# This must wait >1 sec and return 1 (timeout).
+set +e
+${POLL} -I -t 1000 ${EVENT}/hist
+ret=$?
+set -e
+if [ ${ret} != 1 ]; then
+  echo "poll on hist file is not supported"
+  exit_unsupported
+fi
+
+# Test POLLIN
+echo > trace
+echo 'hist:key=comm if comm =="sleep"' > ${EVENT}/trigger
+echo 1 > ${EVENT}/enable
+
+# This sleep command will exit after 2 seconds.
+sleep 2 &
+BGPID=$!
+# if timeout happens, poll returns 1.
+${POLL} -I -t 4000 ${EVENT}/hist
+echo 0 > tracing_on
+
+if [ -d /proc/${BGPID} ]; then
+  echo "poll exits too soon"
+  kill -KILL ${BGPID} ||:
+  exit_fail
+fi
+
+if ! grep -qw "sleep" trace; then
+  echo "poll exits before event happens"
+  exit_fail
+fi
+
+# Test POLLPRI
+echo > trace
+echo 1 > tracing_on
+
+# This sleep command will exit after 2 seconds.
+sleep 2 &
+BGPID=$!
+# if timeout happens, poll returns 1.
+${POLL} -P -t 4000 ${EVENT}/hist
+echo 0 > tracing_on
+
+if [ -d /proc/${BGPID} ]; then
+  echo "poll exits too soon"
+  kill -KILL ${BGPID} ||:
+  exit_fail
+fi
+
+if ! grep -qw "sleep" trace; then
+  echo "poll exits before event happens"
+  exit_fail
+fi
+
+exit_pass
-- 
2.45.2