[PATCH] tracing: Wait for marker writers when copy_trace_marker is cleared

[Pengfei Li]

Clearing copy_trace_marker removes the instance from marker_copies
without waiting for trace_marker writers still walking the list. If the
option is set again right away, a writer on that entry can revisit
instances and write the same marker twice.

Fixes: 7b382efd5e8a ("tracing: Allow the top level trace_marker to write into another instances")
Assisted-by: LLM
Signed-off-by: Pengfei Li <lipengfei28@xxxxxxxxxx>
---
 kernel/trace/trace.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 18710c190c92..b0357f1b5a69 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4016,7 +4016,9 @@ int set_tracer_flag(struct trace_array *tr, u64 mask, int enabled)
 		break;
 
 	case TRACE_ITER(COPY_MARKER):
-		update_marker_trace(tr, enabled);
+		/* Writers of the top level trace_marker may still be on this instance */
+		if (update_marker_trace(tr, enabled) && !enabled)
+			synchronize_rcu();
 		/* update_marker_trace updates the tr->trace_flags */
 		return 0;
 	}

base-commit: 4539944e515183668109bdf4d0c3d7d228383d88
-- 
2.34.1