From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1033049AbdAFTNR (ORCPT ); Fri, 6 Jan 2017 14:13:17 -0500 Received: from mx1.redhat.com ([209.132.183.28]:37208 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934871AbdAFTNI (ORCPT ); Fri, 6 Jan 2017 14:13:08 -0500 Date: Fri, 6 Jan 2017 13:13:01 -0600 From: Josh Poimboeuf To: Miroslav Benes Cc: jeyu@redhat.com, jikos@kernel.org, pmladek@suse.com, corbet@lwn.net, live-patching@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Documentation/livepatch: remove the limitation for schedule() patching Message-ID: <20170106191301.5mlctz7zr7hvzkl5@treble> References: <20170106140045.26331-1-mbenes@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20170106140045.26331-1-mbenes@suse.cz> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Fri, 06 Jan 2017 19:13:04 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 06, 2017 at 03:00:45PM +0100, Miroslav Benes wrote: > The Limitations section of the documentation describes the impossibility > to livepatch anything that is inlined to __schedule() function. This had > been true till 4.9 kernel came. Thanks to commit 0100301bfdf5 > ("sched/x86: Rewrite the switch_to() code") from Brian Gerst there is > __switch_to_asm function now (implemented in assembly) called properly > from context_switch(). RIP is thus saved on the stack and a task would > return to proper version of __schedule() et al. functions. > > Of course __switch_to_asm() is not patchable for the reason described in > the section. But there is no __fentry__ call and I cannot imagine a > reason to do it anyway. > > Therefore, remove the paragraphs from the section. > > Signed-off-by: Miroslav Benes Acked-by: Josh Poimboeuf > --- > FWIW, I also tested this to be sure on top of the consistency model > patch set. I patched schedule() function which calls __schedule() (it is > impossible to patch it directly due to notrace attribute). It works well > except... > > 1. the patching process does not finish, because many tasks sleep in > schedule. STOP/CONT signal does not help. I'll investigate. > > 2. reversion of the process does not work as expected. The kernel > crashes after the removal of the module. A task very likely slept in > schedule and was not migrated properly. It might be because of the races > in klp_reverse_transition() described by Petr, or might be somewhere > else. I'll look into it. Hm, will be interesting to see the cause of this... -- Josh