Commit d162d16d authored Feb 20, 2025 by Sebastian Andrzej Siewior Committed by Wentao Guan Apr 03, 2025

ftrace: Correct preemption accounting for function tracing.

stable inclusion
from stable-v6.6.80
commit ac35a1db03278290faa607d02de2670b9bd72574
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/IBXANC

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ac35a1db03278290faa607d02de2670b9bd72574

--------------------------------

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: ce5e4803 ("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>
(cherry picked from commit ac35a1db03278290faa607d02de2670b9bd72574)
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

parent e5ae728d

kernel/trace/trace_functions.c

+2 −4

Original line number	Diff line number	Diff line
		@@ -185,7 +185,7 @@ 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);
		@@ -285,7 +285,6 @@ 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;

		@@ -312,8 +311,7 @@ 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);