From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752736AbdEPS6k (ORCPT ); Tue, 16 May 2017 14:58:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:35000 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751011AbdEPS6i (ORCPT ); Tue, 16 May 2017 14:58:38 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 991FD23984 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=rostedt@goodmis.org Date: Tue, 16 May 2017 14:58:35 -0400 From: Steven Rostedt To: Masami Hiramatsu Cc: LKML , Thomas Gleixner , Ingo Molnar Subject: [PATCH] kprobes: Document how optimized kprobes are removed from module unload Message-ID: <20170516145835.3827d3aa@gandalf.local.home> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Steven Rostedt (VMware) Thomas discovered a bug where the kprobe trace tests had a race condition where the kprobe_optimizer called from a delayed work queue that does the optimizing and "unoptimizing" of a kprobe, can try to modify the text after it has been freed by the init code. The kprobe trace selftest is a special case, and Thomas and myself investigated to see if there's a chance that this could also be a bug with module unloading, as the code is not obvious to how it handles this. After adding lots of printks, I figured it out. Thomas suggested that this should be commented so that others will not have to go through this exercise again. Suggested-by: Thomas Gleixner Signed-off-by: Steven Rostedt (VMware) --- diff --git a/kernel/kprobes.c b/kernel/kprobes.c index 7367e0e..ac386f6 100644 --- a/kernel/kprobes.c +++ b/kernel/kprobes.c @@ -2183,6 +2183,12 @@ static int kprobes_module_callback(struct notifier_block *nb, * The vaddr this probe is installed will soon * be vfreed buy not synced to disk. Hence, * disarming the breakpoint isn't needed. + * + * Note, this will also move any optimized probes + * that are pending to be removed from their + * corresponding lists to the freeing_list and + * will not be touched by the delayed + * kprobe_optimizer work handler. */ kill_kprobe(p); }