tracepoint: Allow trace events in modules with TAINT_TEST

Commit 2852ca7fba ("panic: Taint kernel if tests are run")
introduced a new taint type, TAINT_TEST, to signal that an
in-kernel test module has been loaded.

TAINT_TEST taint type defaults into a 'bad_taint' list for
kernel tracing and blocks the creation of trace events. This
causes a problem for CXL testing where loading the cxl_test
module makes all CXL modules out-of-tree, blocking any trace
events.

Trace events are in development for CXL at the moment and this
issue was found in test with v6.0-rc1.

Link: https://lkml.kernel.org/r/20220829171048.263065-1-alison.schofield@intel.com

Fixes: 2852ca7fba ("panic: Taint kernel if tests are run")
Reported-by: Ira Weiny <ira.weiny@intel.com>
Suggested-by: Dan Williams <dan.j.williams@intel.com>
Tested-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

kernel/tracepoint.c

@@ -571,7 +571,8 @@ static void for_each_tracepoint_range(
 bool trace_module_has_bad_taint(struct module *mod)
 {
 	return mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP) |
-			       (1 << TAINT_UNSIGNED_MODULE));
+			       (1 << TAINT_UNSIGNED_MODULE) |
+			       (1 << TAINT_TEST));
 }
 
 static BLOCKING_NOTIFIER_HEAD(tracepoint_notify_list);
@@ -647,7 +648,7 @@ static int tracepoint_module_coming(struct module *mod)
 	/*
 	 * We skip modules that taint the kernel, especially those with different
 	 * module headers (for forced load), to make sure we don't cause a crash.
-	 * Staging, out-of-tree, and unsigned GPL modules are fine.
+	 * Staging, out-of-tree, unsigned GPL, and test modules are fine.
 	 */
 	if (trace_module_has_bad_taint(mod))
 		return 0;