tracing: Have tracer option be instance specific

Tracers can add specify options to modify them. This logic was added
before instances were created and the tracer flags were global variables.
After instances were created where a tracer may exist in more than one
instance, the flags were not updated from being global into instance
specific. This causes confusion with these options. For example, the
function tracer has an option to enable function arguments:

  # cd /sys/kernel/tracing
  # mkdir instances/foo
  # echo function > instances/foo/current_tracer
  # echo 1 > options/func-args
  # echo function > current_tracer
  # cat trace
[..]
  <idle>-0       [005] d..3.  1050.656187: rcu_needs_cpu() <-tick_nohz_next_event
  <idle>-0       [005] d..3.  1050.656188: get_next_timer_interrupt(basej=0x10002dbad, basem=0xf45fd7d300) <-tick_nohz_next_event
  <idle>-0       [005] d..3.  1050.656189: _raw_spin_lock(lock=0xffff8944bdf5de80) <-__get_next_timer_interrupt
  <idle>-0       [005] d..4.  1050.656190: do_raw_spin_lock(lock=0xffff8944bdf5de80) <-__get_next_timer_interrupt
  <idle>-0       [005] d..4.  1050.656191: _raw_spin_lock_nested(lock=0xffff8944bdf5f140, subclass=1) <-__get_next_timer_interrupt
 # cat instances/foo/options/func-args
 1
 # cat instances/foo/trace
[..]
  kworker/4:1-88      [004] ...1.   298.127735: next_zone <-refresh_cpu_vm_stats
  kworker/4:1-88      [004] ...1.   298.127736: first_online_pgdat <-refresh_cpu_vm_stats
  kworker/4:1-88      [004] ...1.   298.127738: next_online_pgdat <-refresh_cpu_vm_stats
  kworker/4:1-88      [004] ...1.   298.127739: fold_diff <-refresh_cpu_vm_stats
  kworker/4:1-88      [004] ...1.   298.127741: round_jiffies_relative <-vmstat_update
[..]

The above shows that setting "func-args" in the top level instance also
set it in the instance "foo", but since the interface of the trace flags
are per instance, the update didn't take affect in the "foo" instance.

Update the infrastructure to allow tracers to add a "default_flags" field
in the tracer structure that can be set instead of "flags" which will make
the flags per instance. If a tracer needs to keep the flags global (like
blktrace), keeping the "flags" field set will keep the old behavior.

This does not update function or the function graph tracers. That will be
handled later.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://patch.msgid.link/20251111232429.305317942@kernel.org
Fixes: f20a580627f43 ("ftrace: Allow instances to use function tracing")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 8ecaf91ca823..299862aad66c 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -392,6 +392,7 @@ struct trace_array {
 	int			buffer_percent;
 	unsigned int		n_err_log_entries;
 	struct tracer		*current_trace;
+	struct tracer_flags	*current_trace_flags;
 	u64			trace_flags;
 	unsigned char		trace_flags_index[TRACE_FLAGS_MAX_SIZE];
 	unsigned int		flags;
@@ -406,6 +407,7 @@ struct trace_array {
 	struct list_head	systems;
 	struct list_head	events;
 	struct list_head	marker_list;
+	struct list_head	tracers;
 	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 */
@@ -637,6 +639,7 @@ struct tracer {
 						u64 mask, int set);
 	struct tracer		*next;
 	struct tracer_flags	*flags;
+	struct tracer_flags	*default_flags;
 	int			enabled;
 	bool			print_max;
 	bool			allow_instances;