From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C048FC433F5 for ; Mon, 1 Nov 2021 02:26:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AAB8160F3A for ; Mon, 1 Nov 2021 02:26:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230234AbhKAC3I (ORCPT ); Sun, 31 Oct 2021 22:29:08 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:29618 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230222AbhKAC3F (ORCPT ); Sun, 31 Oct 2021 22:29:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1635733592; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=2CFcDAAKtdRHfDHUO+AtkQWLMsZM3R+b56iEA9NeVjE=; b=i2GvQLWwGNM49xdejioYwjfPQeI9VrOB784wut/u+SBWBhW10ciKqqj49sEMjshkAV5k7K f4zjcpSJM3FSGG9yjkIgcKRh27Af/hPsw3B+KDC9Rsvxx+cw5mFAuts29Ci8FboASJTmAA wB0JiPta/qEypA4KCy2TdlWywFJzEPU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-234-UM0ma7m2MEieqWFDyeih2g-1; Sun, 31 Oct 2021 22:26:29 -0400 X-MC-Unique: UM0ma7m2MEieqWFDyeih2g-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DD93C80668C; Mon, 1 Nov 2021 02:26:27 +0000 (UTC) Received: from redhat.com (unknown [10.22.16.72]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4048C60D30; Mon, 1 Nov 2021 02:26:20 +0000 (UTC) Date: Sun, 31 Oct 2021 22:26:18 -0400 From: Joe Lawrence To: Ming Lei Cc: Josh Poimboeuf , Jiri Kosina , Miroslav Benes , Petr Mladek , live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Luis Chamberlain Subject: Re: [PATCH 0/3] livepatch: cleanup kpl_patch kobject release Message-ID: References: <20211028125734.3134176-1-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 30, 2021 at 12:36:28AM +0800, Ming Lei wrote: > On Fri, Oct 29, 2021 at 09:51:54AM -0400, Joe Lawrence wrote: > > On Thu, Oct 28, 2021 at 08:57:31PM +0800, Ming Lei wrote: > > > Hello, > > > > > > The 1st patch moves module_put() to release handler of klp_patch > > > kobject. > > > > > > The 2nd patch changes to free klp_patch and other kobjects without > > > klp_mutex. > > > > > > The 3rd patch switches to synchronous kobject release for klp_patch. > > > > > > > Hi Ming, > > > > I gave the patchset a spin on top of linus tree @ 1fc596a56b33 and ended > > up with a stuck task: > > > > Test > > ---- > > Enable the livepatch selftests: > > $ grep CONFIG_TEST_LIVEPATCH .config > > CONFIG_TEST_LIVEPATCH=m > > > > Run a continuous kernel build in the background: > > $ while (true); do make clean && make -j$(nproc); done > > > > While continuously executing the selftests: > > $ while (true); do make -C tools/testing/selftests/livepatch/ run_tests; done > > > > Results > > ------- > > Hello Joe, > > Thanks for the test! > > Can you replace the 3rd patch with the following one then running the test again? > > From 599e96f79aebc388ef3854134312c6039a7884bf Mon Sep 17 00:00:00 2001 > From: Ming Lei > Date: Thu, 28 Oct 2021 20:11:23 +0800 > Subject: [PATCH 3/3] livepatch: free klp_patch object synchronously > > klp_mutex isn't acquired before calling kobject_put(klp_patch), so it is > fine to free klp_patch object synchronously. > > One issue is that enabled store() method, in which the klp_patch kobject > itself is deleted & released. However, sysfs has provided APIs for dealing > with this corner case, so use sysfs_break_active_protection() and > sysfs_unbreak_active_protection() for releasing klp_patch kobject from > enabled_store(). > > Signed-off-by: Ming Lei > --- > include/linux/livepatch.h | 1 - > kernel/livepatch/core.c | 32 +++++++++++++------------------- > kernel/livepatch/core.h | 2 +- > kernel/livepatch/transition.c | 2 +- > 4 files changed, 15 insertions(+), 22 deletions(-) > > diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h > index 9712818997c5..4dcebf52fac5 100644 > --- a/include/linux/livepatch.h > +++ b/include/linux/livepatch.h > @@ -169,7 +169,6 @@ struct klp_patch { > struct list_head obj_list; > bool enabled; > bool forced; > - struct work_struct free_work; > }; > > #define klp_for_each_object_static(patch, obj) \ > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c > index 9ede093d699a..6cfc54f6bdcc 100644 > --- a/kernel/livepatch/core.c > +++ b/kernel/livepatch/core.c > @@ -337,6 +337,7 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr, > int ret; > bool enabled; > LIST_HEAD(to_free); > + struct kernfs_node *kn = NULL; > > ret = kstrtobool(buf, &enabled); > if (ret) > @@ -369,7 +370,14 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr, > out: > mutex_unlock(&klp_mutex); > > - klp_free_patches_async(&to_free); > + if (list_empty(&to_free)) { > + kn = sysfs_break_active_protection(kobj, &attr->attr); > + WARN_ON_ONCE(!kn); > + sysfs_remove_file(kobj, &attr->attr); > + klp_free_patches(&to_free); > + if (kn) > + sysfs_unbreak_active_protection(kn); > + } > > if (ret) > return ret; > @@ -684,32 +692,19 @@ static void klp_free_patch_finish(struct klp_patch *patch) > kobject_put(&patch->kobj); > } > > -/* > - * The livepatch might be freed from sysfs interface created by the patch. > - * This work allows to wait until the interface is destroyed in a separate > - * context. > - */ > -static void klp_free_patch_work_fn(struct work_struct *work) > -{ > - struct klp_patch *patch = > - container_of(work, struct klp_patch, free_work); > - > - klp_free_patch_finish(patch); > -} > - > -static void klp_free_patch_async(struct klp_patch *patch) > +static void klp_free_patch(struct klp_patch *patch) > { > klp_free_patch_start(patch); > - schedule_work(&patch->free_work); > + klp_free_patch_finish(patch); > } > > -void klp_free_patches_async(struct list_head *to_free) > +void klp_free_patches(struct list_head *to_free) > { > struct klp_patch *patch, *tmp_patch; > > list_for_each_entry_safe(patch, tmp_patch, to_free, list) { > list_del_init(&patch->list); > - klp_free_patch_async(patch); > + klp_free_patch(patch); > } > } > > @@ -873,7 +868,6 @@ static int klp_init_patch_early(struct klp_patch *patch) > kobject_init(&patch->kobj, &klp_ktype_patch); > patch->enabled = false; > patch->forced = false; > - INIT_WORK(&patch->free_work, klp_free_patch_work_fn); > > klp_for_each_object_static(patch, obj) { > if (!obj->funcs) > diff --git a/kernel/livepatch/core.h b/kernel/livepatch/core.h > index 8ff97745ba40..ea593f370049 100644 > --- a/kernel/livepatch/core.h > +++ b/kernel/livepatch/core.h > @@ -13,7 +13,7 @@ extern struct list_head klp_patches; > #define klp_for_each_patch(patch) \ > list_for_each_entry(patch, &klp_patches, list) > > -void klp_free_patches_async(struct list_head *to_free); > +void klp_free_patches(struct list_head *to_free); > void klp_unpatch_replaced_patches(struct klp_patch *new_patch); > void klp_discard_nops(struct klp_patch *new_patch); > > diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c > index a9ebc9c5db02..3eff5fc0deee 100644 > --- a/kernel/livepatch/transition.c > +++ b/kernel/livepatch/transition.c > @@ -41,7 +41,7 @@ static void klp_transition_work_fn(struct work_struct *work) > > mutex_unlock(&klp_mutex); > > - klp_free_patches_async(&to_free); > + klp_free_patches(&to_free); > } > static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn); > > -- > 2.31.1 > > Hi Ming, The previous test runs without hung tasks, but I noticed that is probably because the selftests quickly wedge. A simple reproducer for that: # (background load) % while(true); do make clean && make -j$(nproc); done vs. # (selftests) % while(true); do ./tools/testing/selftests/livepatch/test-livepatch.sh || break; done TEST: basic function patching ... ok TEST: multiple livepatches ... ok TEST: atomic replace livepatch ... ok TEST: basic function patching ... ok TEST: multiple livepatches ... ok TEST: atomic replace livepatch ... ok TEST: basic function patching ... ok TEST: multiple livepatches ... ERROR: failed to disable livepatch test_klp_livepatch % lsmod | grep test_klp test_klp_livepatch 16384 1 % cat /sys/kernel/livepatch/test_klp_livepatch/enabled 0 % rmmod test_klp_livepatch rmmod: ERROR: Module test_klp_livepatch is in use [ 249.870587] ===== TEST: multiple livepatches ===== [ 249.885520] % modprobe test_klp_livepatch [ 249.916987] livepatch: enabling patch 'test_klp_livepatch' [ 249.923131] livepatch: 'test_klp_livepatch': initializing patching transition [ 249.925575] livepatch: 'test_klp_livepatch': starting patching transition [ 249.934215] livepatch: 'test_klp_livepatch': completing patching transition [ 249.934337] livepatch: 'test_klp_livepatch': patching complete [ 249.946294] test_klp_livepatch: this has been live patched [ 249.963337] % modprobe test_klp_atomic_replace replace=0 [ 249.996371] livepatch: enabling patch 'test_klp_atomic_replace' [ 250.002998] livepatch: 'test_klp_atomic_replace': initializing patching transition [ 250.005333] livepatch: 'test_klp_atomic_replace': starting patching transition [ 250.014364] livepatch: 'test_klp_atomic_replace': completing patching transition [ 250.014471] livepatch: 'test_klp_atomic_replace': patching complete [ 250.027259] test_klp_livepatch: this has been live patched [ 250.036050] test_klp_atomic_replace: this has been live patched [ 250.046347] % echo 0 > /sys/kernel/livepatch/test_klp_atomic_replace/enabled [ 250.054403] livepatch: 'test_klp_atomic_replace': initializing unpatching transition [ 250.054574] livepatch: 'test_klp_atomic_replace': starting unpatching transition [ 251.764849] livepatch: 'test_klp_atomic_replace': completing unpatching transition [ 251.799266] livepatch: 'test_klp_atomic_replace': unpatching complete [ 251.911706] % rmmod test_klp_atomic_replace [ 251.970438] test_klp_livepatch: this has been live patched [ 251.980347] % echo 0 > /sys/kernel/livepatch/test_klp_livepatch/enabled [ 251.987936] livepatch: 'test_klp_livepatch': initializing unpatching transition [ 251.988115] livepatch: 'test_klp_livepatch': starting unpatching transition [ 251.997033] livepatch: 'test_klp_livepatch': completing unpatching transition [ 252.027090] livepatch: 'test_klp_livepatch': unpatching complete [ 313.289932] ERROR: failed to disable livepatch test_klp_livepatch In this case, the "failed to disable" msg occurs because the sysfs interface / module remain present. -- Joe