On 11/29/2018 06:18 AM, Dan Carpenter wrote: > Hi Waiman, > > Thank you for the patch! Perhaps something to improve: > > url: https://github.com/0day-ci/linux/commits/Waiman-Long/cgroup-Introducing-bypass-mode/20181123-030552 > base: https://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-next > > smatch warnings: > kernel/cgroup/cgroup.c:4893 css_create() error: we previously assumed 'parent' could be null (see line 4864) > > # https://github.com/0day-ci/linux/commit/8b68fd4330e043645667a5d3306398f8f88f9ff2 > git remote add linux-review https://github.com/0day-ci/linux > git remote update linux-review > git checkout 8b68fd4330e043645667a5d3306398f8f88f9ff2 > vim +/parent +4893 kernel/cgroup/cgroup.c > > a31f2d3ff kernel/cgroup.c Tejun Heo 2012-11-19 4840 > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4841 /** > 6cd0f5bba kernel/cgroup.c Tejun Heo 2016-03-03 4842 * css_create - create a cgroup_subsys_state > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4843 * @cgrp: the cgroup new css will be associated with > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4844 * @ss: the subsys of new css > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4845 * > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4846 * Create a new css associated with @cgrp - @ss pair. On success, the new > 6cd0f5bba kernel/cgroup.c Tejun Heo 2016-03-03 4847 * css is online and installed in @cgrp. This function doesn't create the > 6cd0f5bba kernel/cgroup.c Tejun Heo 2016-03-03 4848 * interface files. Returns 0 on success, -errno on failure. > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4849 */ > 6cd0f5bba kernel/cgroup.c Tejun Heo 2016-03-03 4850 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp, > 6cd0f5bba kernel/cgroup.c Tejun Heo 2016-03-03 4851 struct cgroup_subsys *ss) > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4852 { > d51f39b05 kernel/cgroup.c Tejun Heo 2014-05-16 4853 struct cgroup *parent = cgroup_parent(cgrp); > 8b68fd433 kernel/cgroup/cgroup.c Waiman Long 2018-11-20 4854 struct cgroup_subsys_state *parent_css = NULL; > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4855 struct cgroup_subsys_state *css; > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4856 int err; > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4857 > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4858 lockdep_assert_held(&cgroup_mutex); > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4859 > 8b68fd433 kernel/cgroup/cgroup.c Waiman Long 2018-11-20 4860 /* > 8b68fd433 kernel/cgroup/cgroup.c Waiman Long 2018-11-20 4861 * As cgroup may be in bypass mode, need to skip over ancestor > 8b68fd433 kernel/cgroup/cgroup.c Waiman Long 2018-11-20 4862 * cgroups with NULL CSS. > 8b68fd433 kernel/cgroup/cgroup.c Waiman Long 2018-11-20 4863 */ > 8b68fd433 kernel/cgroup/cgroup.c Waiman Long 2018-11-20 @4864 for (; parent && !parent_css; parent = cgroup_parent(parent)) > ^^^^^^^^^^^^^^^^^^^^^ > 8b68fd433 kernel/cgroup/cgroup.c Waiman Long 2018-11-20 4865 parent_css = cgroup_css(parent, ss); > > When we exit this loop it means either parent is NULL or parent_css > is non-NULL. Sorry for the bug. I should have a temp variable to go up cgroup_parent() iteration chain and leave parent alone. Thanks for spotting that. > 8b68fd433 kernel/cgroup/cgroup.c Waiman Long 2018-11-20 4866 > 1fed1b2e3 kernel/cgroup.c Tejun Heo 2014-05-16 4867 css = ss->css_alloc(parent_css); > e7e15b87f kernel/cgroup.c Tejun Heo 2016-06-21 4868 if (!css) > e7e15b87f kernel/cgroup.c Tejun Heo 2016-06-21 4869 css = ERR_PTR(-ENOMEM); > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4870 if (IS_ERR(css)) > 6cd0f5bba kernel/cgroup.c Tejun Heo 2016-03-03 4871 return css; > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4872 > 8b68fd433 kernel/cgroup/cgroup.c Waiman Long 2018-11-20 4873 init_and_link_css(css, ss, cgrp, parent_css); > a2bed8209 kernel/cgroup.c Tejun Heo 2014-05-04 4874 > 2aad2a86f kernel/cgroup.c Tejun Heo 2014-09-24 4875 err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL); > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4876 if (err) > 3eb59ec64 kernel/cgroup.c Li Zefan 2014-03-18 4877 goto err_free_css; > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4878 > cf780b7dc kernel/cgroup.c Vladimir Davydov 2015-08-03 4879 err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL); > 15a4c835e kernel/cgroup.c Tejun Heo 2014-05-04 4880 if (err < 0) > b00c52dae kernel/cgroup.c Wenwei Tao 2016-05-13 4881 goto err_free_css; > 15a4c835e kernel/cgroup.c Tejun Heo 2014-05-04 4882 css->id = err; > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4883 > 15a4c835e kernel/cgroup.c Tejun Heo 2014-05-04 4884 /* @css is ready to be brought online now, make it visible */ > 1fed1b2e3 kernel/cgroup.c Tejun Heo 2014-05-16 4885 list_add_tail_rcu(&css->sibling, &parent_css->children); > 15a4c835e kernel/cgroup.c Tejun Heo 2014-05-04 4886 cgroup_idr_replace(&ss->css_idr, css, css->id); > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4887 > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4888 err = online_css(css); > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4889 if (err) > 1fed1b2e3 kernel/cgroup.c Tejun Heo 2014-05-16 4890 goto err_list_del; > 944196278 kernel/cgroup.c Tejun Heo 2014-03-19 4891 > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4892 if (ss->broken_hierarchy && !ss->warned_broken_hierarchy && > d51f39b05 kernel/cgroup.c Tejun Heo 2014-05-16 @4893 cgroup_parent(parent)) { > ^^^^^^ > We dereference parent inside the function, but I don't know for sure > if this is reachable when "parent" is NULL. > > ed3d261b5 kernel/cgroup.c Joe Perches 2014-04-25 4894 pr_warn("%s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n", > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4895 current->comm, current->pid, ss->name); > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4896 if (!strcmp(ss->name, "memory")) > ed3d261b5 kernel/cgroup.c Joe Perches 2014-04-25 4897 pr_warn("\"memory\" requires setting use_hierarchy to 1 on the root\n"); > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4898 ss->warned_broken_hierarchy = true; > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4899 } > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4900 > 6cd0f5bba kernel/cgroup.c Tejun Heo 2016-03-03 4901 return css; > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4902 > 1fed1b2e3 kernel/cgroup.c Tejun Heo 2014-05-16 4903 err_list_del: > 1fed1b2e3 kernel/cgroup.c Tejun Heo 2014-05-16 4904 list_del_rcu(&css->sibling); > 3eb59ec64 kernel/cgroup.c Li Zefan 2014-03-18 4905 err_free_css: > 8f53470ba kernel/cgroup/cgroup.c Tejun Heo 2018-04-26 4906 list_del_rcu(&css->rstat_css_node); > 8f36aaec9 kernel/cgroup/cgroup.c Tejun Heo 2018-03-14 4907 INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn); > 8f36aaec9 kernel/cgroup/cgroup.c Tejun Heo 2018-03-14 4908 queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork); > 6cd0f5bba kernel/cgroup.c Tejun Heo 2016-03-03 4909 return ERR_PTR(err); > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4910 } > c81c925ad kernel/cgroup.c Tejun Heo 2013-12-06 4911 > > --- > 0-DAY kernel test infrastructure Open Source Technology Center > https://lists.01.org/pipermail/kbuild-all Intel Corporation Cheers, Longman
