kasan: disable LOCKDEP when printing reports

If LOCKDEP detects a bug while KASAN is printing a report and if
panic_on_warn is set, KASAN will not be able to finish.  Disable LOCKDEP
while KASAN is printing a report.

See https://bugzilla.kernel.org/show_bug.cgi?id=202115 for an example
of the issue.

Link: https://lkml.kernel.org/r/c48a2a3288200b07e1788b77365c2f02784cfeb4.1646237226.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/kasan/report.c

@@ -13,6 +13,7 @@
 #include <linux/ftrace.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
+#include <linux/lockdep.h>
 #include <linux/mm.h>
 #include <linux/printk.h>
 #include <linux/sched.h>
@@ -148,6 +149,8 @@ static void start_report(unsigned long *flags, bool sync)
 	disable_trace_on_warning();
 	/* Update status of the currently running KASAN test. */
 	update_kunit_status(sync);
+	/* Do not allow LOCKDEP mangling KASAN reports. */
+	lockdep_off();
 	/* Make sure we don't end up in loop. */
 	kasan_disable_current();
 	spin_lock_irqsave(&report_lock, *flags);
@@ -160,12 +163,13 @@ static void end_report(unsigned long *flags, void *addr)
 		trace_error_report_end(ERROR_DETECTOR_KASAN,
 				       (unsigned long)addr);
 	pr_err("==================================================================\n");
-	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 	spin_unlock_irqrestore(&report_lock, *flags);
 	if (panic_on_warn && !test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
 		panic("panic_on_warn set ...\n");
 	if (kasan_arg_fault == KASAN_ARG_FAULT_PANIC)
 		panic("kasan.fault=panic set ...\n");
+	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
+	lockdep_on();
 	kasan_enable_current();
 }