Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755281AbbK0S4r (ORCPT ); Fri, 27 Nov 2015 13:56:47 -0500 Received: from mx1.redhat.com ([209.132.183.28]:43102 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755264AbbK0S4k (ORCPT ); Fri, 27 Nov 2015 13:56:40 -0500 Date: Fri, 27 Nov 2015 19:57:19 +0100 From: Oleg Nesterov To: Aleksa Sarai , Johannes Weiner , Li Zefan , Tejun Heo Cc: linux-kernel@vger.kernel.org Subject: [PATCH 1/3] cgroup: pids: fix race between cgroup_post_fork() and cgroup_migrate() Message-ID: <20151127185719.GA14682@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151127185705.GA14669@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3115 Lines: 92 If the new child migrates to another cgroup before cgroup_post_fork() calls subsys->fork(), then both pids_can_attach() and pids_fork() will do the same pids_uncharge(old_pids) + pids_charge(pids) sequence twice. Change copy_process() to call threadgroup_change_begin/threadgroup_change_end unconditionally. percpu_down_read() is cheap and this allows other cleanups, see the next changes. Also, this way we can unify cgroup_threadgroup_rwsem and dup_mmap_sem. Signed-off-by: Oleg Nesterov --- kernel/cgroup_pids.c | 21 ++------------------- kernel/fork.c | 9 +++------ 2 files changed, 5 insertions(+), 25 deletions(-) diff --git a/kernel/cgroup_pids.c b/kernel/cgroup_pids.c index cdd8df4..15ef2e4 100644 --- a/kernel/cgroup_pids.c +++ b/kernel/cgroup_pids.c @@ -243,27 +243,10 @@ static void pids_cancel_fork(struct task_struct *task, void *priv) static void pids_fork(struct task_struct *task, void *priv) { - struct cgroup_subsys_state *css; - struct cgroup_subsys_state *old_css = priv; - struct pids_cgroup *pids; - struct pids_cgroup *old_pids = css_pids(old_css); - - css = task_get_css(task, pids_cgrp_id); - pids = css_pids(css); - - /* - * If the association has changed, we have to revert and reapply the - * charge/uncharge on the wrong hierarchy to the current one. Since - * the association can only change due to an organisation event, its - * okay for us to ignore the limit in this case. - */ - if (pids != old_pids) { - pids_uncharge(old_pids, 1); - pids_charge(pids, 1); - } + struct cgroup_subsys_state *css = priv; + WARN_ON(task_css_check(task, pids_cgrp_id, true) != css); css_put(css); - css_put(old_css); } static void pids_free(struct task_struct *task) diff --git a/kernel/fork.c b/kernel/fork.c index f97f2c4..fce002e 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1368,8 +1368,7 @@ static struct task_struct *copy_process(unsigned long clone_flags, p->real_start_time = ktime_get_boot_ns(); p->io_context = NULL; p->audit_context = NULL; - if (clone_flags & CLONE_THREAD) - threadgroup_change_begin(current); + threadgroup_change_begin(current); cgroup_fork(p); #ifdef CONFIG_NUMA p->mempolicy = mpol_dup(p->mempolicy); @@ -1610,8 +1609,7 @@ static struct task_struct *copy_process(unsigned long clone_flags, proc_fork_connector(p); cgroup_post_fork(p, cgrp_ss_priv); - if (clone_flags & CLONE_THREAD) - threadgroup_change_end(current); + threadgroup_change_end(current); perf_event_fork(p); trace_task_newtask(p, clone_flags); @@ -1652,8 +1650,7 @@ bad_fork_cleanup_policy: mpol_put(p->mempolicy); bad_fork_cleanup_threadgroup_lock: #endif - if (clone_flags & CLONE_THREAD) - threadgroup_change_end(current); + threadgroup_change_end(current); delayacct_tsk_free(p); bad_fork_cleanup_count: atomic_dec(&p->cred->user->processes); -- 1.5.5.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/