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.

[akpm@linux-foundation.org: add comma to enum list, per Andy]

Link: https://lkml.kernel.org/r/20211115085630.1756817-1-elver@google.comSigned-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: Linus Torvalds <torvalds@linux-foundation.org>