kcsan: test: don't put the expect array on the stack

Size of the 'expect' array in the __report_matches is 1536 bytes, which
is exactly the default frame size warning limit of the xtensa
architecture.
As a result allmodconfig xtensa kernel builds with the gcc that does not
support the compiler plugins (which otherwise would push the said
warning limit to 2K) fail with the following message:

  kernel/kcsan/kcsan_test.c:257:1: error: the frame size of 1680 bytes
    is larger than 1536 bytes

Fix it by dynamically allocating the 'expect' array.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Reviewed-by: Marco Elver <elver@google.com>
Tested-by: Marco Elver <elver@google.com>

kernel/kcsan/kcsan_test.c

@@ -159,7 +159,7 @@ static bool __report_matches(const struct expect_report *r)
 	const bool is_assert = (r->access[0].type | r->access[1].type) & KCSAN_ACCESS_ASSERT;
 	bool ret = false;
 	unsigned long flags;
-	typeof(observed.lines) expect;
+	typeof(*observed.lines) *expect;
 	const char *end;
 	char *cur;
 	int i;
@@ -168,6 +168,10 @@ static bool __report_matches(const struct expect_report *r)
 	if (!report_available())
 		return false;
 
+	expect = kmalloc(sizeof(observed.lines), GFP_KERNEL);
+	if (WARN_ON(!expect))
+		return false;
+
 	/* Generate expected report contents. */
 
 	/* Title */
@@ -253,6 +257,7 @@ static bool __report_matches(const struct expect_report *r)
 		strstr(observed.lines[2], expect[1])));
 out:
 	spin_unlock_irqrestore(&observed.lock, flags);
+	kfree(expect);
 	return ret;
 }