Commit c897c1e5 authored by Nam Cao's avatar Nam Cao Committed by Steven Rostedt (Google)
Browse files

tracing: Remove pointless memory barriers 

Memory barriers are useful to ensure memory accesses from one CPU appear in
the original order as seen by other CPUs.

Some smp_rmb() and smp_wmb() are used, but they are not ordering multiple
memory accesses.

Remove them.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Gabriele Monaco <gmonaco@redhat.com>
Link: https://lore.kernel.org/20250626151940.1756398-1-namcao@linutronix.de


Signed-off-by: default avatarNam Cao <namcao@linutronix.de>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 878e1e94

kernel/trace/rv/rv.c

+0 −6
Original line number Diff line number Diff line
@@ -675,8 +675,6 @@ static bool __read_mostly monitoring_on; 
 */

bool rv_monitoring_on(void)

{

	/* Ensures that concurrent monitors read consistent monitoring_on */

	smp_rmb();

	return READ_ONCE(monitoring_on);

}
@@ -696,8 +694,6 @@ static ssize_t monitoring_on_read_data(struct file *filp, char __user *user_buf, 
static void turn_monitoring_off(void)

{

	WRITE_ONCE(monitoring_on, false);

	/* Ensures that concurrent monitors read consistent monitoring_on */

	smp_wmb();

}



static void reset_all_monitors(void)
@@ -713,8 +709,6 @@ static void reset_all_monitors(void) 
static void turn_monitoring_on(void)

{

	WRITE_ONCE(monitoring_on, true);

	/* Ensures that concurrent monitors read consistent monitoring_on */

	smp_wmb();

}



static void turn_monitoring_on_with_reset(void)

kernel/trace/trace.c

+0 −7
Original line number Diff line number Diff line
@@ -936,7 +936,6 @@ int tracing_is_enabled(void) 
	 * return the mirror variable of the state of the ring buffer.

	 * It's a little racy, but we don't really care.

	 */

	smp_rmb();

	return !global_trace.buffer_disabled;

}
@@ -1107,8 +1106,6 @@ void tracer_tracing_on(struct trace_array *tr) 
	 * important to be fast than accurate.

	 */

	tr->buffer_disabled = 0;

	/* Make the flag seen by readers */

	smp_wmb();

}



/**
@@ -1640,8 +1637,6 @@ void tracer_tracing_off(struct trace_array *tr) 
	 * important to be fast than accurate.

	 */

	tr->buffer_disabled = 1;

	/* Make the flag seen by readers */

	smp_wmb();

}



/**
@@ -2710,8 +2705,6 @@ void trace_buffered_event_enable(void) 


static void enable_trace_buffered_event(void *data)

{

	/* Probably not needed, but do it anyway */

	smp_rmb();

	this_cpu_dec(trace_buffered_event_cnt);

}