ftrace: Correct preemption accounting for function tracing.

The function tracer should record the preemption level at the point when
the function is invoked. If the tracing subsystem decrement the
preemption counter it needs to correct this before feeding the data into
the trace buffer. This was broken in the commit cited below while
shifting the preempt-disabled section.

Use tracing_gen_ctx_dec() which properly subtracts one from the
preemption counter on a preemptible kernel.

Cc: stable@vger.kernel.org
Cc: Wander Lairson Costa <wander@redhat.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/20250220140749.pfw8qoNZ@linutronix.de
Fixes: ce5e48036c9e7 ("ftrace: disable preemption when recursion locked")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Wander Lairson Costa <wander@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index d358c9935164de99a93e7403af358838ede4f892..df56f9b76010943a0673122fbc46d353a8018bb4 100644 (file)
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -216,7 +216,7 @@ function_trace_call(unsigned long ip, unsigned long parent_ip,
 
        parent_ip = function_get_true_parent_ip(parent_ip, fregs);
 
-       trace_ctx = tracing_gen_ctx();
+       trace_ctx = tracing_gen_ctx_dec();
 
        data = this_cpu_ptr(tr->array_buffer.data);
        if (!atomic_read(&data->disabled))
@@ -321,7 +321,6 @@ function_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
        struct trace_array *tr = op->private;
        struct trace_array_cpu *data;
        unsigned int trace_ctx;
-       unsigned long flags;
        int bit;
 
        if (unlikely(!tr->function_enabled))
@@ -347,8 +346,7 @@ function_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
        if (is_repeat_check(tr, last_info, ip, parent_ip))
                goto out;
 
-       local_save_flags(flags);
-       trace_ctx = tracing_gen_ctx_flags(flags);
+       trace_ctx = tracing_gen_ctx_dec();
        process_repeats(tr, ip, parent_ip, last_info, trace_ctx);
 
        trace_function(tr, ip, parent_ip, trace_ctx);