[PATCH v2 2/2] tracing/snapshot: Use work_on_cpu to avoid -EBUSY during snapshot swap

The snapshot operation currently uses smp_call_function_single() to
invoke ring_buffer_swap_cpu() on the target CPU. Since interrupt can hit
at any point during the write path, this may return -EBUSY if the target
CPU is actively writing to the buffer, which could be confusing to users
who may not understand the internal state of the ring buffer.

Replace smp_call_function_single() with work_on_cpu() for the snapshot
operation. This ensures that the swap only occurs after the ongoing
write completes.

Signed-off-by: Tengda Wu <[email protected]>
---
 kernel/trace/trace_snapshot.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_snapshot.c b/kernel/trace/trace_snapshot.c
index 07b43c9863a2..22323c97289b 100644
--- a/kernel/trace/trace_snapshot.c
+++ b/kernel/trace/trace_snapshot.c
@@ -625,9 +625,12 @@ static int tracing_snapshot_open(struct inode *inode, struct file *file)
 	return ret;
 }
 
-static void tracing_swap_cpu_buffer(void *tr)
+static long tracing_swap_cpu_buffer(void *tr)
 {
+	local_irq_disable();
 	update_max_tr_single((struct trace_array *)tr, current, smp_processor_id());
+	local_irq_enable();
+	return 0;
 }
 
 static ssize_t
@@ -689,8 +692,7 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
 			update_max_tr(tr, current, smp_processor_id(), NULL);
 			local_irq_enable();
 		} else {
-			smp_call_function_single(iter->cpu_file, tracing_swap_cpu_buffer,
-						 (void *)tr, 1);
+			work_on_cpu(iter->cpu_file, tracing_swap_cpu_buffer, (void *)tr);
 		}
 		tracing_disarm_snapshot(tr);
 		break;
-- 
2.34.1