[PATCH v2] tracing: Keep copying markers when one instance is stopped

[Jaewon Jung <jaewon8868@gmail.com>]

When several instances enable copy_trace_marker, stopping one instance
can prevent the remaining buffers from receiving markers.

Continue copying text and raw markers even if one copy fails. Return the
last write's result, keeping -ENODEV when no destinations are selected.

Fixes: 7b382efd5e8a ("tracing: Allow the top level trace_marker to write into another instances")
Signed-off-by: Jaewon Jung <jaewon8868@gmail.com>
---
All writes are now attempted regardless of errors.
The last write's result is returned. Would this approach work?

Changes in v2:
- Drop the stable Cc.
- Do not save earlier copy errors. Return the last write's result.
- Rebase onto trace/for-next.

Tested on x86_64 QEMU:
- Before: Copying stops at the first error, which is returned.
  Later live buffers receive no markers.
- After: All buffers are tried, and the last write's result is returned.
- Existing text/raw marker and instance selftests: 6 PASS.

 kernel/trace/trace.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 08614af8fad1..0b66c55d378b 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6330,8 +6330,6 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
 		guard(rcu)();
 		list_for_each_entry_rcu(tr, &marker_copies, marker_list) {
 			written = write_marker_to_buffer(tr, buf, cnt, ip);
-			if (written < 0)
-				break;
 		}
 	} else {
 		written = write_marker_to_buffer(tr, buf, cnt, ip);
@@ -6409,8 +6407,6 @@ tracing_mark_raw_write(struct file *filp, const char __user *ubuf,
 		guard(rcu)();
 		list_for_each_entry_rcu(tr, &marker_copies, marker_list) {
 			written = write_raw_marker_to_buffer(tr, buf, cnt);
-			if (written < 0)
-				break;
 		}
 	} else {
 		written = write_raw_marker_to_buffer(tr, buf, cnt);

base-commit: d7ff48d92a0f28bc0612da47c054efbc28c19562
-- 
2.43.0