From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753294AbbCJOWx (ORCPT ); Tue, 10 Mar 2015 10:22:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43140 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753105AbbCJOWt (ORCPT ); Tue, 10 Mar 2015 10:22:49 -0400 Date: Tue, 10 Mar 2015 09:22:04 -0500 From: Josh Poimboeuf To: Petr Mladek Cc: Seth Jennings , Jiri Kosina , Rusty Russell , Miroslav Benes , Masami Hiramatsu , mingo@kernel.org, mathieu.desnoyers@efficios.com, oleg@redhat.com, paulmck@linux.vnet.ibm.com, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, andi@firstfloor.org, rostedt@goodmis.org, tglx@linutronix.de Subject: Re: [PATCH v3] livepatch/module: Correctly handle coming and going modules Message-ID: <20150310142204.GK10815@treble.redhat.com> References: <1425907528-22976-1-git-send-email-pmladek@suse.cz> <20150309144055.GA10815@treble.redhat.com> <20150310120103.GC1813@dhcp128.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20150310120103.GC1813@dhcp128.suse.cz> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 10, 2015 at 01:01:07PM +0100, Petr Mladek wrote: > On Mon 2015-03-09 09:40:55, Josh Poimboeuf wrote: > > On Mon, Mar 09, 2015 at 02:25:28PM +0100, Petr Mladek wrote: > > > + > > > mutex_unlock(&module_mutex); > > > } > > > > > > @@ -736,6 +748,7 @@ static int klp_init_object(struct klp_patch *patch, struct klp_object *obj) > > > return -EINVAL; > > > > > > obj->state = KLP_DISABLED; > > > + obj->mod = NULL; > > > > > > klp_find_object_module(obj); > > > > > > @@ -926,6 +939,15 @@ static int klp_module_notify(struct notifier_block *nb, unsigned long action, > > > > > > mutex_lock(&klp_mutex); > > > > > > + /* > > > + * Each module has to know that the notifier has been called. > > > + * We never know what module will get patched by a new patch. > > > + */ > > > + if (action == MODULE_STATE_COMING) > > > + mod->klp_alive = true; > > > + else /* MODULE_STATE_GOING */ > > > + mod->klp_alive = false; > > > + > > > > Any reason why this needs to be protected by the mutex? > > We need to synchronize it with the check in > klp_find_object_module(). Otherwise, for example, the check might read > "true" and add/enable new patch but this notify handler will be > blocked until the patch is added => it will mess the order of > patches. > > It might be more clean to take module_mutex here but the value is > needed only by livepatching, so klp_mutex seems to be enough. Ah, right. Looks good to me. > > > list_for_each_entry(patch, &klp_patches, list) { > > > for (obj = patch->objs; obj->funcs; obj++) { > > > if (!klp_is_module(obj) || strcmp(obj->name, mod->name)) > > > diff --git a/kernel/module.c b/kernel/module.c > > > index d856e96a3cce..b3ffc231ce0d 100644 > > > --- a/kernel/module.c > > > +++ b/kernel/module.c > > > @@ -3271,6 +3271,10 @@ static int load_module(struct load_info *info, const char __user *uargs, > > > } > > > #endif > > > > > > +#ifdef CONFIG_LIVEPATCH > > > + mod->klp_alive = false; > > > +#endif > > > + > > > > I don't think you need this initialization. It looks like the module > > struct is embedded in the mod->module_core region which is initialized > > to zero in move_module(). > > I have looked at this before but I was not able to find a code > zeroing struct module. If I get it correctly, mod->module_core > is a location where symbol table sections are copied or so. Yeah, it's far from obvious. AFAICT, it's cleared by the "memset(ptr, 0, mod->core_size)" line. -- Josh