[PATCH v2] ftrace: Fix stack trace entry generated by ftrace_pid_func()

[Tatsuya S]

On setting set_ftrace_pid, a extra entry generated by ftrace_pid_func()
is shown on stack trace(CONFIG_UNWINDER_FRAME_POINTER=y).

        [004] .....    68.459382: <stack trace>
 => 0xffffffffa00090af
 => ksys_read
 => __x64_sys_read
 => x64_sys_call
 => do_syscall_64
 => entry_SYSCALL_64_after_hwframe

To resolve this issue, increment skip count
in function_stack_trace_call() if pids are set.

Signed-off-by: Tatsuya S <tatsuya.s2862@xxxxxxxxx>
---
Changes in v2:
    - Fix build warnings reported by kernel test robot
    - Link to v1: https://lore.kernel.org/linux-trace-kernel/20240526112658.46740-1-tatsuya.s2862@xxxxxxxxx/

 include/linux/ftrace.h         | 2 ++
 kernel/trace/ftrace.c          | 2 +-
 kernel/trace/trace_functions.c | 7 ++++++-
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 800995c425e0..0855dfe768eb 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -913,6 +913,8 @@ static inline bool is_ftrace_trampoline(unsigned long addr)
 /* totally disable ftrace - can not re-enable after this */
 void ftrace_kill(void);
 
+bool ftrace_pids_enabled(struct ftrace_ops *ops);
+
 static inline void tracer_disable(void)
 {
 #ifdef CONFIG_FUNCTION_TRACER
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 65208d3b5ed9..e8ddd56d1e55 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -99,7 +99,7 @@ struct ftrace_ops *function_trace_op __read_mostly = &ftrace_list_end;
 /* What to set function_trace_op to */
 static struct ftrace_ops *set_function_trace_op;
 
-static bool ftrace_pids_enabled(struct ftrace_ops *ops)
+bool ftrace_pids_enabled(struct ftrace_ops *ops)
 {
 	struct trace_array *tr;
 
diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 9f1bfbe105e8..455c9a880199 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -223,6 +223,7 @@ function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
 	long disabled;
 	int cpu;
 	unsigned int trace_ctx;
+	int skip = STACK_SKIP;
 
 	if (unlikely(!tr->function_enabled))
 		return;
@@ -239,7 +240,11 @@ function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
 	if (likely(disabled == 1)) {
 		trace_ctx = tracing_gen_ctx_flags(flags);
 		trace_function(tr, ip, parent_ip, trace_ctx);
-		__trace_stack(tr, trace_ctx, STACK_SKIP);
+#ifdef CONFIG_UNWINDER_FRAME_POINTER
+		if (ftrace_pids_enabled(op))
+			skip++;
+#endif
+		__trace_stack(tr, trace_ctx, skip);
 	}
 
 	atomic_dec(&data->disabled);
-- 
2.45.1