From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751987AbdEQCqH (ORCPT ); Tue, 16 May 2017 22:46:07 -0400 Received: from mail.kernel.org ([198.145.29.99]:39006 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751337AbdEQCqF (ORCPT ); Tue, 16 May 2017 22:46:05 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 317D6239DA 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 22:46:02 -0400 From: Steven Rostedt To: Masami Hiramatsu Cc: LKML , Thomas Gleixner , Ingo Molnar Subject: Re: [PATCH] kprobes: Document how optimized kprobes are removed from module unload Message-ID: <20170516224602.6a6dc420@gandalf.local.home> In-Reply-To: <20170517104707.f2fe0e8baa0adb3c8ece74db@kernel.org> References: <20170516145835.3827d3aa@gandalf.local.home> <20170517104707.f2fe0e8baa0adb3c8ece74db@kernel.org> 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 On Wed, 17 May 2017 10:47:07 +0900 Masami Hiramatsu wrote: > On Tue, 16 May 2017 14:58:35 -0400 > Steven Rostedt wrote: > > > 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. > > > > OK, and I prefer this comment to move into kill_kprobe() right > before calling kill_optimized_kprobe() because that actually > does it. Actually, I can add a comment in both places. I didn't put it into kill_kprobe() because, yes that's where it is done. I placed it in the module handler because that's where one will look to see if module unloading doesn't have any race conditions with the delayed handling. -- Steve > > Thank you, > > > 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); > > } > >