Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755825Ab2JPW3Q (ORCPT ); Tue, 16 Oct 2012 18:29:16 -0400 Received: from mail-pa0-f46.google.com ([209.85.220.46]:63115 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755741Ab2JPW3G (ORCPT ); Tue, 16 Oct 2012 18:29:06 -0400 From: Tejun Heo To: rjw@sisk.pl, oleg@redhat.com Cc: linux-kernel@vger.kernel.org, lizefan@huawei.com, containers@lists.linux-foundation.org, cgroups@vger.kernel.org, Tejun Heo Subject: [PATCH 7/7] cgroup_freezer: don't use cgroup_lock_live_group() Date: Tue, 16 Oct 2012 15:28:46 -0700 Message-Id: <1350426526-14254-8-git-send-email-tj@kernel.org> X-Mailer: git-send-email 1.7.7.3 In-Reply-To: <1350426526-14254-1-git-send-email-tj@kernel.org> References: <1350426526-14254-1-git-send-email-tj@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5220 Lines: 149 freezer_read/write() used cgroup_lock_live_group() to synchronize against task migration into and out of the target cgroup. cgroup_lock_live_group() grabs the internal cgroup lock and using it from outside cgroup core leads to complex and fragile locking dependency issues which are difficult to resolve. Now that freezer_can_attach() is replaced with freezer_attach() and update_if_frozen() updated, nothing requires excluding migration against freezer state reads and changes. This patch removes cgroup_lock_live_group() and the matching cgroup_unlock() usages. The prone-to-bitrot, already outdated and unnecessary global lock hierarchy documentation is replaced with documentation in local scope. Signed-off-by: Tejun Heo Cc: Oleg Nesterov Cc: Rafael J. Wysocki Cc: Li Zefan --- kernel/cgroup_freezer.c | 66 +++++++--------------------------------------- 1 files changed, 10 insertions(+), 56 deletions(-) diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c index 3d45503..8a92b0e 100644 --- a/kernel/cgroup_freezer.c +++ b/kernel/cgroup_freezer.c @@ -84,50 +84,6 @@ static const char *freezer_state_strs[] = { struct cgroup_subsys freezer_subsys; -/* Locks taken and their ordering - * ------------------------------ - * cgroup_mutex (AKA cgroup_lock) - * freezer->lock - * css_set_lock - * task->alloc_lock (AKA task_lock) - * task->sighand->siglock - * - * cgroup code forces css_set_lock to be taken before task->alloc_lock - * - * freezer_create(), freezer_destroy(): - * cgroup_mutex [ by cgroup core ] - * - * freezer_can_attach(): - * cgroup_mutex (held by caller of can_attach) - * - * freezer_fork() (preserving fork() performance means can't take cgroup_mutex): - * freezer->lock - * sighand->siglock (if the cgroup is freezing) - * - * freezer_read(): - * cgroup_mutex - * freezer->lock - * write_lock css_set_lock (cgroup iterator start) - * task->alloc_lock - * read_lock css_set_lock (cgroup iterator start) - * - * freezer_write() (freeze): - * cgroup_mutex - * freezer->lock - * write_lock css_set_lock (cgroup iterator start) - * task->alloc_lock - * read_lock css_set_lock (cgroup iterator start) - * sighand->siglock (fake signal delivery inside freeze_task()) - * - * freezer_write() (unfreeze): - * cgroup_mutex - * freezer->lock - * write_lock css_set_lock (cgroup iterator start) - * task->alloc_lock - * read_lock css_set_lock (cgroup iterator start) - * task->alloc_lock (inside __thaw_task(), prevents race with refrigerator()) - * sighand->siglock - */ static struct cgroup_subsys_state *freezer_create(struct cgroup *cgroup) { struct freezer *freezer; @@ -151,9 +107,13 @@ static void freezer_destroy(struct cgroup *cgroup) } /* - * The call to cgroup_lock() in the freezer.state write method prevents - * a write to that file racing against an attach, and hence we don't need - * to worry about racing against migration. + * Tasks can be migrated into a different freezer anytime regardless of its + * current state. freezer_attach() is responsible for making new tasks + * conform to the current state. + * + * Freezer state changes and task migration are synchronized via + * @freezer->lock. freezer_attach() makes the new tasks conform to the + * current state and all following state changes can see the new tasks. */ static void freezer_attach(struct cgroup *new_cgrp, struct cgroup_taskset *tset) { @@ -217,8 +177,8 @@ out: * partially frozen when we exitted write. Caller must hold freezer->lock. * * Task states and freezer state might disagree while tasks are being - * migrated into @cgroup, so we can't verify task states against @freezer - * state here. See freezer_attach() for details. + * migrated into or out of @cgroup, so we can't verify task states against + * @freezer state here. See freezer_attach() for details. */ static void update_if_frozen(struct cgroup *cgroup, struct freezer *freezer) { @@ -255,15 +215,11 @@ static int freezer_read(struct cgroup *cgroup, struct cftype *cft, struct freezer *freezer; enum freezer_state state; - if (!cgroup_lock_live_group(cgroup)) - return -ENODEV; - freezer = cgroup_freezer(cgroup); spin_lock_irq(&freezer->lock); update_if_frozen(cgroup, freezer); state = freezer->state; spin_unlock_irq(&freezer->lock); - cgroup_unlock(); seq_puts(m, freezer_state_strs[state]); seq_putc(m, '\n'); @@ -297,6 +253,7 @@ static void freezer_change_state(struct cgroup *cgroup, { struct freezer *freezer = cgroup_freezer(cgroup); + /* also synchronizes against task migration, see freezer_attach() */ spin_lock_irq(&freezer->lock); switch (goal_state) { @@ -332,10 +289,7 @@ static int freezer_write(struct cgroup *cgroup, else return -EINVAL; - if (!cgroup_lock_live_group(cgroup)) - return -ENODEV; freezer_change_state(cgroup, goal_state); - cgroup_unlock(); return 0; } -- 1.7.7.3 -- 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/