linux-kernel - [PATCH 2/2] tracing: Disable events in reverse order of their enable operation

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Date:   Mon, 27 Nov 2023 16:12:48 +0100
From:   Petr Pavlu <petr.pavlu@...e.com>
To:     rostedt@...dmis.org, mhiramat@...nel.org,
        mathieu.desnoyers@...icios.com
Cc:     zhengyejian1@...wei.com, linux-trace-kernel@...r.kernel.org,
        linux-kernel@...r.kernel.org, Petr Pavlu <petr.pavlu@...e.com>
Subject: [PATCH 2/2] tracing: Disable events in reverse order of their enable operation

Make the disable operation in __ftrace_event_enable_disable() use the
reverse order of the respective enable operation.

This has two minor benefits:
* Disabling of buffered events via trace_buffered_event_disable() is
  done after unregistering the trace event. It closes a small window
  where an event would be still registered and could be hit, but would
  unnecessarily go directly to a ring buffer.
* The SOFT_DISABLED flag is now consistently set only when SOFT_MODE is
  also set.

Signed-off-by: Petr Pavlu <petr.pavlu@...e.com>
---
 kernel/trace/trace_events.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index f29e815ca5b2..5f14d68a0ced 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -633,9 +633,6 @@ static int __ftrace_event_enable_disable(struct trace_event_file *file,
 			if (atomic_dec_return(&file->sm_ref) > 0)
 				break;
 			disable = file->flags & EVENT_FILE_FL_SOFT_DISABLED;
-			clear_bit(EVENT_FILE_FL_SOFT_MODE_BIT, &file->flags);
-			/* Disable use of trace_buffered_event */
-			trace_buffered_event_disable();
 		} else
 			disable = !(file->flags & EVENT_FILE_FL_SOFT_MODE);
 
@@ -653,11 +650,17 @@ static int __ftrace_event_enable_disable(struct trace_event_file *file,
 
 			call->class->reg(call, TRACE_REG_UNREGISTER, file);
 		}
-		/* If in SOFT_MODE, just set the SOFT_DISABLE_BIT, else clear it */
-		if (file->flags & EVENT_FILE_FL_SOFT_MODE)
-			set_bit(EVENT_FILE_FL_SOFT_DISABLED_BIT, &file->flags);
-		else
+
+		if (soft_disable) {
+			/* Complete going out of SOFT_MODE */
 			clear_bit(EVENT_FILE_FL_SOFT_DISABLED_BIT, &file->flags);
+			clear_bit(EVENT_FILE_FL_SOFT_MODE_BIT, &file->flags);
+			/* Disable use of trace_buffered_event */
+			trace_buffered_event_disable();
+		} else if (file->flags & EVENT_FILE_FL_SOFT_MODE) {
+			/* If in SOFT_MODE, just set the SOFT_DISABLE_BIT */
+			set_bit(EVENT_FILE_FL_SOFT_DISABLED_BIT, &file->flags);
+		}
 		break;
 	case 1:
 		/*
-- 
2.35.3