From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965152AbbEMUfu (ORCPT ); Wed, 13 May 2015 16:35:50 -0400 Received: from mail-qk0-f172.google.com ([209.85.220.172]:34595 "EHLO mail-qk0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934422AbbEMUfd (ORCPT ); Wed, 13 May 2015 16:35:33 -0400 From: Tejun Heo To: lizefan@huawei.com Cc: cgroups@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, linux-kernel@vger.kernel.org, Tejun Heo Subject: [PATCH 3/3] cgroup: simplify threadgroup locking Date: Wed, 13 May 2015 16:35:18 -0400 Message-Id: <1431549318-16756-4-git-send-email-tj@kernel.org> X-Mailer: git-send-email 2.1.0 In-Reply-To: <1431549318-16756-1-git-send-email-tj@kernel.org> References: <1431549318-16756-1-git-send-email-tj@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Now that threadgroup locking is made global, code paths around it can be simplified. * lock-verify-unlock-retry dancing removed from __cgroup_procs_write(). * Race protection against de_thread() removed from cgroup_update_dfl_csses(). Signed-off-by: Tejun Heo --- kernel/cgroup.c | 48 +++++++++++++----------------------------------- 1 file changed, 13 insertions(+), 35 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 5435b9d..afe9a7e 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2401,14 +2401,13 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf, if (!cgrp) return -ENODEV; -retry_find_task: + percpu_down_write(&cgroup_threadgroup_rwsem); rcu_read_lock(); if (pid) { tsk = find_task_by_vpid(pid); if (!tsk) { - rcu_read_unlock(); ret = -ESRCH; - goto out_unlock_cgroup; + goto out_unlock_rcu; } /* * even if we're attaching all tasks in the thread group, we @@ -2418,9 +2417,8 @@ retry_find_task: if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) && !uid_eq(cred->euid, tcred->uid) && !uid_eq(cred->euid, tcred->suid)) { - rcu_read_unlock(); ret = -EACCES; - goto out_unlock_cgroup; + goto out_unlock_rcu; } } else tsk = current; @@ -2435,35 +2433,21 @@ retry_find_task: */ if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) { ret = -EINVAL; - rcu_read_unlock(); - goto out_unlock_cgroup; + goto out_unlock_rcu; } get_task_struct(tsk); rcu_read_unlock(); - percpu_down_write(&cgroup_threadgroup_rwsem); - if (threadgroup) { - if (!thread_group_leader(tsk)) { - /* - * a race with de_thread from another thread's exec() - * may strip us of our leadership, if this happens, - * there is no choice but to throw this task away and - * try again; this is - * "double-double-toil-and-trouble-check locking". - */ - percpu_up_write(&cgroup_threadgroup_rwsem); - put_task_struct(tsk); - goto retry_find_task; - } - } - ret = cgroup_attach_task(cgrp, tsk, threadgroup); - percpu_up_write(&cgroup_threadgroup_rwsem); - put_task_struct(tsk); -out_unlock_cgroup: + goto out_unlock_threadgroup; + +out_unlock_rcu: + rcu_read_unlock(); +out_unlock_threadgroup: + percpu_up_write(&cgroup_threadgroup_rwsem); cgroup_kn_unlock(of->kn); return ret ?: nbytes; } @@ -2610,6 +2594,8 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp) lockdep_assert_held(&cgroup_mutex); + percpu_down_write(&cgroup_threadgroup_rwsem); + /* look up all csses currently attached to @cgrp's subtree */ down_read(&css_set_rwsem); css_for_each_descendant_pre(css, cgroup_css(cgrp, NULL)) { @@ -2665,17 +2651,8 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp) goto out_finish; last_task = task; - percpu_down_write(&cgroup_threadgroup_rwsem); - /* raced against de_thread() from another thread? */ - if (!thread_group_leader(task)) { - percpu_up_write(&cgroup_threadgroup_rwsem); - put_task_struct(task); - continue; - } - ret = cgroup_migrate(src_cset->dfl_cgrp, task, true); - percpu_up_write(&cgroup_threadgroup_rwsem); put_task_struct(task); if (WARN(ret, "cgroup: failed to update controllers for the default hierarchy (%d), further operations may crash or hang\n", ret)) @@ -2685,6 +2662,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp) out_finish: cgroup_migrate_finish(&preloaded_csets); + percpu_up_write(&cgroup_threadgroup_rwsem); return ret; } -- 2.1.0