[PATCH] tracing: Fix to avoid creating trace instances with duplicate names

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Since commit e645535a954a ("tracing: Add option to use memmapped
memory for trace boot instance") changed trace_array_get_by_name() to
trace_array_create_systems(), enable_instances() does not reuse the
same name instance. Therefore, if an administrator mistakenly specifies
multiple `trace_instance=` options with duplicate names, all are
created but only the first is accessible via tracefs.

Check whether an instance with the same name already exists before
creating a new one, and reject duplicates with a warning.

Fixes: e645535a954a ("tracing: Add option to use memmapped memory for trace boot instance")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 kernel/trace/trace.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a946e0183fd1..536e71f28d51 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -9651,6 +9651,11 @@ __init static void enable_instances(void)
 		if (flag_delim)
 			*flag_delim++ = '\0';
 
+		if (trace_array_find(name)) {
+			pr_warn("Tracing: Instance %s already exists\n", name);
+			continue;
+		}
+
 		if (backup) {
 			if (backup_instance_area(backup, &addr, &size) < 0)
 				continue;