kdb: Fix handling of kallsyms_symbol_next() return value

kallsyms_symbol_next() returns a boolean (true on success). Currently
kdb_read() tests the return value with an inequality that
unconditionally evaluates to true.

This is fixed in the obvious way and, since the conditional branch is
supposed to be unreachable, we also add a WARN_ON().

Reported-by: Dan Carpenter <[email protected]>
Signed-off-by: Daniel Thompson <[email protected]>
Cc: linux-stable <[email protected]>
Signed-off-by: Jason Wessel <[email protected]>

kernel/debug/kdb/kdb_io.c

@@ -350,7 +350,7 @@ static char *kdb_read(char *buffer, size_t bufsize)
 			}
 			kdb_printf("\n");
 			for (i = 0; i < count; i++) {
-				if (kallsyms_symbol_next(p_tmp, i) < 0)
+				if (WARN_ON(!kallsyms_symbol_next(p_tmp, i)))
 					break;
 				kdb_printf("%s ", p_tmp);
 				*(p_tmp + len) = '\0';