Commit 7b382efd authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt (Google)
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tracing: Allow the top level trace_marker to write into another instances 

There are applications that have it hard coded to write into the top level
trace_marker instance (/sys/kernel/tracing/trace_marker). This can be
annoying if a profiler is using that instance for other work, or if it
needs all writes to go into a new instance.

A new option is created called "copy_trace_marker". By default, the top
level has this set, as that is the default buffer that writing into the
top level trace_marker file will go to. But now if an instance is created
and sets this option, all writes into the top level trace_marker will also
be written into that instance buffer just as if an application were to
write into the instance's trace_marker file.

If the top level instance disables this option, then writes to its own
trace_marker and trace_marker_raw files will not go into its buffer.

If no instance has this option set, then the write will return an error
and errno will contain ENODEV.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/20250508095639.39f84eda@gandalf.local.home


Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 6956ea9f

Documentation/trace/ftrace.rst

+13 −0
Original line number Diff line number Diff line
@@ -1205,6 +1205,19 @@ Here are the available options: 
	default instance. The only way the top level instance has this flag

	cleared, is by it being set in another instance.



  copy_trace_marker

	If there are applications that hard code writing into the top level

	trace_marker file (/sys/kernel/tracing/trace_marker or trace_marker_raw),

	and the tooling would like it to go into an instance, this option can

	be used. Create an instance and set this option, and then all writes

	into the top level trace_marker file will also be redirected into this

	instance.



	Note, by default this option is set for the top level instance. If it

	is disabled, then writes to the trace_marker or trace_marker_raw files

	will not be written into the top level file. If no instance has this

	option set, then a write will error with the errno of ENODEV.



  annotate

	It is sometimes confusing when the CPU buffers are full

	and one CPU buffer had a lot of events recently, thus

kernel/trace/trace.c

+113 −31
Original line number Diff line number Diff line
@@ -493,7 +493,8 @@ EXPORT_SYMBOL_GPL(unregister_ftrace_export); 
	 TRACE_ITER_ANNOTATE | TRACE_ITER_CONTEXT_INFO |		\

	 TRACE_ITER_RECORD_CMD | TRACE_ITER_OVERWRITE |			\

	 TRACE_ITER_IRQ_INFO | TRACE_ITER_MARKERS |			\

	 TRACE_ITER_HASH_PTR | TRACE_ITER_TRACE_PRINTK)

	 TRACE_ITER_HASH_PTR | TRACE_ITER_TRACE_PRINTK |		\

	 TRACE_ITER_COPY_MARKER)



/* trace_options that are only supported by global_trace */

#define TOP_LEVEL_TRACE_FLAGS (TRACE_ITER_PRINTK |			\
@@ -501,7 +502,8 @@ EXPORT_SYMBOL_GPL(unregister_ftrace_export); 


/* trace_flags that are default zero for instances */

#define ZEROED_TRACE_FLAGS \

	(TRACE_ITER_EVENT_FORK | TRACE_ITER_FUNC_FORK | TRACE_ITER_TRACE_PRINTK)

	(TRACE_ITER_EVENT_FORK | TRACE_ITER_FUNC_FORK | TRACE_ITER_TRACE_PRINTK | \

	 TRACE_ITER_COPY_MARKER)



/*

 * The global_trace is the descriptor that holds the top-level tracing
@@ -513,6 +515,9 @@ static struct trace_array global_trace = { 


static struct trace_array *printk_trace = &global_trace;



/* List of trace_arrays interested in the top level trace_marker */

static LIST_HEAD(marker_copies);



static __always_inline bool printk_binsafe(struct trace_array *tr)

{

	/*
@@ -534,6 +539,28 @@ static void update_printk_trace(struct trace_array *tr) 
	tr->trace_flags |= TRACE_ITER_TRACE_PRINTK;

}



/* Returns true if the status of tr changed */

static bool update_marker_trace(struct trace_array *tr, int enabled)

{

	lockdep_assert_held(&event_mutex);



	if (enabled) {

		if (!list_empty(&tr->marker_list))

			return false;



		list_add_rcu(&tr->marker_list, &marker_copies);

		tr->trace_flags |= TRACE_ITER_COPY_MARKER;

		return true;

	}



	if (list_empty(&tr->marker_list))

		return false;



	list_del_init(&tr->marker_list);

	tr->trace_flags &= ~TRACE_ITER_COPY_MARKER;

	return true;

}



void trace_set_ring_buffer_expanded(struct trace_array *tr)

{

	if (!tr)
@@ -5220,7 +5247,8 @@ int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled) 
{

	if ((mask == TRACE_ITER_RECORD_TGID) ||

	    (mask == TRACE_ITER_RECORD_CMD) ||

	    (mask == TRACE_ITER_TRACE_PRINTK))

	    (mask == TRACE_ITER_TRACE_PRINTK) ||

	    (mask == TRACE_ITER_COPY_MARKER))

		lockdep_assert_held(&event_mutex);



	/* do nothing if flag is already set */
@@ -5251,6 +5279,9 @@ int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled) 
		}

	}



	if (mask == TRACE_ITER_COPY_MARKER)

		update_marker_trace(tr, enabled);



	if (enabled)

		tr->trace_flags |= mask;

	else
@@ -7134,11 +7165,9 @@ tracing_free_buffer_release(struct inode *inode, struct file *filp) 


#define TRACE_MARKER_MAX_SIZE		4096



static ssize_t

tracing_mark_write(struct file *filp, const char __user *ubuf,

					size_t cnt, loff_t *fpos)

static ssize_t write_marker_to_buffer(struct trace_array *tr, const char __user *ubuf,

				      size_t cnt, unsigned long ip)

{

	struct trace_array *tr = filp->private_data;

	struct ring_buffer_event *event;

	enum event_trigger_type tt = ETT_NONE;

	struct trace_buffer *buffer;
@@ -7152,18 +7181,6 @@ tracing_mark_write(struct file *filp, const char __user *ubuf, 
#define FAULTED_STR "<faulted>"

#define FAULTED_SIZE (sizeof(FAULTED_STR) - 1) /* '\0' is already accounted for */



	if (tracing_disabled)

		return -EINVAL;



	if (!(tr->trace_flags & TRACE_ITER_MARKERS))

		return -EINVAL;



	if ((ssize_t)cnt < 0)

		return -EINVAL;



	if (cnt > TRACE_MARKER_MAX_SIZE)

		cnt = TRACE_MARKER_MAX_SIZE;



	meta_size = sizeof(*entry) + 2;  /* add '\0' and possible '\n' */

 again:

	size = cnt + meta_size;
@@ -7196,7 +7213,7 @@ tracing_mark_write(struct file *filp, const char __user *ubuf, 
	}



	entry = ring_buffer_event_data(event);

	entry->ip = _THIS_IP_;

	entry->ip = ip;



	len = __copy_from_user_inatomic(&entry->buf, ubuf, cnt);

	if (len) {
@@ -7229,18 +7246,12 @@ tracing_mark_write(struct file *filp, const char __user *ubuf, 
}



static ssize_t

tracing_mark_raw_write(struct file *filp, const char __user *ubuf,

tracing_mark_write(struct file *filp, const char __user *ubuf,

					size_t cnt, loff_t *fpos)

{

	struct trace_array *tr = filp->private_data;

	struct ring_buffer_event *event;

	struct trace_buffer *buffer;

	struct raw_data_entry *entry;

	ssize_t written;

	int size;

	int len;



#define FAULT_SIZE_ID (FAULTED_SIZE + sizeof(int))

	ssize_t written = -ENODEV;

	unsigned long ip;



	if (tracing_disabled)

		return -EINVAL;
@@ -7248,10 +7259,42 @@ tracing_mark_raw_write(struct file *filp, const char __user *ubuf, 
	if (!(tr->trace_flags & TRACE_ITER_MARKERS))

		return -EINVAL;



	/* The marker must at least have a tag id */

	if (cnt < sizeof(unsigned int))

	if ((ssize_t)cnt < 0)

		return -EINVAL;



	if (cnt > TRACE_MARKER_MAX_SIZE)

		cnt = TRACE_MARKER_MAX_SIZE;



	/* The selftests expect this function to be the IP address */

	ip = _THIS_IP_;



	/* The global trace_marker can go to multiple instances */

	if (tr == &global_trace) {

		guard(rcu)();

		list_for_each_entry_rcu(tr, &marker_copies, marker_list) {

			written = write_marker_to_buffer(tr, ubuf, cnt, ip);

			if (written < 0)

				break;

		}

	} else {

		written = write_marker_to_buffer(tr, ubuf, cnt, ip);

	}



	return written;

}



static ssize_t write_raw_marker_to_buffer(struct trace_array *tr,

					  const char __user *ubuf, size_t cnt)

{

	struct ring_buffer_event *event;

	struct trace_buffer *buffer;

	struct raw_data_entry *entry;

	ssize_t written;

	int size;

	int len;



#define FAULT_SIZE_ID (FAULTED_SIZE + sizeof(int))



	size = sizeof(*entry) + cnt;

	if (cnt < FAULT_SIZE_ID)

		size += FAULT_SIZE_ID - cnt;
@@ -7282,6 +7325,40 @@ tracing_mark_raw_write(struct file *filp, const char __user *ubuf, 
	return written;

}



static ssize_t

tracing_mark_raw_write(struct file *filp, const char __user *ubuf,

					size_t cnt, loff_t *fpos)

{

	struct trace_array *tr = filp->private_data;

	ssize_t written = -ENODEV;



#define FAULT_SIZE_ID (FAULTED_SIZE + sizeof(int))



	if (tracing_disabled)

		return -EINVAL;



	if (!(tr->trace_flags & TRACE_ITER_MARKERS))

		return -EINVAL;



	/* The marker must at least have a tag id */

	if (cnt < sizeof(unsigned int))

		return -EINVAL;



	/* The global trace_marker_raw can go to multiple instances */

	if (tr == &global_trace) {

		guard(rcu)();

		list_for_each_entry_rcu(tr, &marker_copies, marker_list) {

			written = write_raw_marker_to_buffer(tr, ubuf, cnt);

			if (written < 0)

				break;

		}

	} else {

		written = write_raw_marker_to_buffer(tr, ubuf, cnt);

	}



	return written;

}



static int tracing_clock_show(struct seq_file *m, void *v)

{

	struct trace_array *tr = m->private;
@@ -9775,6 +9852,7 @@ trace_array_create_systems(const char *name, const char *systems, 
	INIT_LIST_HEAD(&tr->events);

	INIT_LIST_HEAD(&tr->hist_vars);

	INIT_LIST_HEAD(&tr->err_log);

	INIT_LIST_HEAD(&tr->marker_list);



#ifdef CONFIG_MODULES

	INIT_LIST_HEAD(&tr->mod_events);
@@ -9934,6 +10012,9 @@ static int __remove_instance(struct trace_array *tr) 
	if (printk_trace == tr)

		update_printk_trace(&global_trace);



	if (update_marker_trace(tr, 0))

		synchronize_rcu();



	tracing_set_nop(tr);

	clear_ftrace_function_probes(tr);

	event_trace_del_tracer(tr);
@@ -10999,6 +11080,7 @@ __init static int tracer_alloc_buffers(void) 
	INIT_LIST_HEAD(&global_trace.events);

	INIT_LIST_HEAD(&global_trace.hist_vars);

	INIT_LIST_HEAD(&global_trace.err_log);

	list_add(&global_trace.marker_list, &marker_copies);

	list_add(&global_trace.list, &ftrace_trace_arrays);



	apply_trace_boot_options();

kernel/trace/trace.h

+2 −0
Original line number Diff line number Diff line
@@ -403,6 +403,7 @@ struct trace_array { 
	struct trace_options	*topts;

	struct list_head	systems;

	struct list_head	events;

	struct list_head	marker_list;

	struct trace_event_file *trace_marker_file;

	cpumask_var_t		tracing_cpumask; /* only trace on set CPUs */

	/* one per_cpu trace_pipe can be opened by only one user */
@@ -1384,6 +1385,7 @@ extern int trace_get_user(struct trace_parser *parser, const char __user *ubuf, 
		C(MARKERS,		"markers"),		\

		C(EVENT_FORK,		"event-fork"),		\

		C(TRACE_PRINTK,		"trace_printk_dest"),	\

		C(COPY_MARKER,		"copy_trace_marker"),\

		C(PAUSE_ON_TRACE,	"pause-on-trace"),	\

		C(HASH_PTR,		"hash-ptr"),	/* Print hashed pointer */ \

		FUNCTION_FLAGS					\