panic: use error_report_end tracepoint on warnings

Introduce the error detector "warning" to the error_report event and use
the error_report_end tracepoint at the end of a warning report.

This allows in-kernel tests but also userspace to more easily determine
if a warning occurred without polling kernel logs.

Link: https://lkml.kernel.org/r/20211115085630.1756817-1-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Alexander Popov <alex.popov@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

include/trace/events/error_report.h

@@ -17,14 +17,16 @@
 
 enum error_detector {
 	ERROR_DETECTOR_KFENCE,
-	ERROR_DETECTOR_KASAN
+	ERROR_DETECTOR_KASAN,
+	ERROR_DETECTOR_WARN
 };
 
 #endif /* __ERROR_REPORT_DECLARE_TRACE_ENUMS_ONCE_ONLY */
 
-#define error_detector_list	\
+#define error_detector_list			\
 	EM(ERROR_DETECTOR_KFENCE, "kfence")	\
-	EMe(ERROR_DETECTOR_KASAN, "kasan")
+	EM(ERROR_DETECTOR_KASAN, "kasan")	\
+	EMe(ERROR_DETECTOR_WARN, "warning")
 /* Always end the list with an EMe. */
 
 #undef EM

kernel/panic.c

@@ -32,6 +32,7 @@
 #include <linux/bug.h>
 #include <linux/ratelimit.h>
 #include <linux/debugfs.h>
+#include <trace/events/error_report.h>
 #include <asm/sections.h>
 
 #define PANIC_TIMER_STEP 100
@@ -609,6 +610,7 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
 	print_irqtrace_events(current);
 
 	print_oops_end_marker();
+	trace_error_report_end(ERROR_DETECTOR_WARN, (unsigned long)caller);
 
 	/* Just a warning, don't kill lockdep. */
 	add_taint(taint, LOCKDEP_STILL_OK);