ftrace: Correct preemption accounting for function tracing.

commit 57b76bedc5c52c66968183b5ef57234894c25ce7 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 3b0cea37e0297b0e6e84f0663830e1fd92562196..fbbc3c719d2f68c9bfa8eaf64864191a639d5594 100644 (file)
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -193,7 +193,7 @@ function_trace_call(unsigned long ip, unsigned long parent_ip,
        if (bit < 0)
                return;
 
-       trace_ctx = tracing_gen_ctx();
+       trace_ctx = tracing_gen_ctx_dec();
 
        cpu = smp_processor_id();
        data = per_cpu_ptr(tr->array_buffer.data, cpu);
@@ -298,7 +298,6 @@ 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;
        int cpu;
 
@@ -325,8 +324,7 @@ 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);