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Date: Thu, 25 Aug 2011 02:07:35 -0700
From: Paul Menage <paul@...lmenage.org>
To: Tejun Heo <tj@...nel.org>
Cc: rjw@...k.pl, lizf@...fujitsu.com,
linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
containers@...ts.linux-foundation.org,
Balbir Singh <bsingharora@...il.com>,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
James Morris <jmorris@...ei.org>, Ingo Molnar <mingo@...e.hu>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 4/6] cgroup: don't use subsys->can_attach_task() or ->attach_task()
On Tue, Aug 23, 2011 at 3:19 PM, Tejun Heo <tj@...nel.org> wrote:
> Now that subsys->can_attach() and attach() take @tset instead of
> @task, they can handle per-task operations. Convert
> ->can_attach_task() and ->attach_task() users to use ->can_attach()
> and attach() instead. Most converions are straight-forward.
> Noteworthy changes are,
>
> * In cgroup_freezer, remove unnecessary NULL assignments to unused
> methods. It's useless and very prone to get out of sync, which
> already happened.
>
> * In cpuset, PF_THREAD_BOUND test is checked for each task. This
> doesn't make any practical difference but is conceptually cleaner.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Paul Menage <paul@...lmenage.org>
> Cc: Li Zefan <lizf@...fujitsu.com>
> Cc: Balbir Singh <bsingharora@...il.com>
> Cc: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Cc: James Morris <jmorris@...ei.org>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Peter Zijlstra <peterz@...radead.org>
> ---
> block/blk-cgroup.c | 45 +++++++++++++++++++-----------
> kernel/cgroup_freezer.c | 14 +++-------
> kernel/cpuset.c | 70 +++++++++++++++++++++-------------------------
> kernel/events/core.c | 13 +++++---
> kernel/sched.c | 31 +++++++++++++--------
> 5 files changed, 91 insertions(+), 82 deletions(-)
>
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index bcaf16e..99e0bd4 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -30,8 +30,10 @@ EXPORT_SYMBOL_GPL(blkio_root_cgroup);
>
> static struct cgroup_subsys_state *blkiocg_create(struct cgroup_subsys *,
> struct cgroup *);
> -static int blkiocg_can_attach_task(struct cgroup *, struct task_struct *);
> -static void blkiocg_attach_task(struct cgroup *, struct task_struct *);
> +static int blkiocg_can_attach(struct cgroup_subsys *, struct cgroup *,
> + struct cgroup_taskset *);
> +static void blkiocg_attach(struct cgroup_subsys *, struct cgroup *,
> + struct cgroup_taskset *);
> static void blkiocg_destroy(struct cgroup_subsys *, struct cgroup *);
> static int blkiocg_populate(struct cgroup_subsys *, struct cgroup *);
>
> @@ -44,8 +46,8 @@ static int blkiocg_populate(struct cgroup_subsys *, struct cgroup *);
> struct cgroup_subsys blkio_subsys = {
> .name = "blkio",
> .create = blkiocg_create,
> - .can_attach_task = blkiocg_can_attach_task,
> - .attach_task = blkiocg_attach_task,
> + .can_attach = blkiocg_can_attach,
> + .attach = blkiocg_attach,
> .destroy = blkiocg_destroy,
> .populate = blkiocg_populate,
> #ifdef CONFIG_BLK_CGROUP
> @@ -1614,30 +1616,39 @@ done:
> * of the main cic data structures. For now we allow a task to change
> * its cgroup only if it's the only owner of its ioc.
> */
> -static int blkiocg_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
> +static int blkiocg_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
> + struct cgroup_taskset *tset)
> {
> + struct task_struct *task;
> struct io_context *ioc;
> int ret = 0;
>
> /* task_lock() is needed to avoid races with exit_io_context() */
> - task_lock(tsk);
> - ioc = tsk->io_context;
> - if (ioc && atomic_read(&ioc->nr_tasks) > 1)
> - ret = -EINVAL;
> - task_unlock(tsk);
> -
> + cgroup_taskset_for_each(task, cgrp, tset) {
> + task_lock(task);
> + ioc = task->io_context;
> + if (ioc && atomic_read(&ioc->nr_tasks) > 1)
> + ret = -EINVAL;
> + task_unlock(task);
> + if (ret)
> + break;
> + }
Doesn't the other part of this patch set, that avoids calling the
*attach() methods for tasks that aren't moving, eliminate the need for
the usage of skip_cgrp here (and elsewhere)? When do we actually need
to pass a non-NULL skip_cgrp to cgroup_taskset_for_each()?
Paul
> return ret;
> }
>
> -static void blkiocg_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
> +static void blkiocg_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
> + struct cgroup_taskset *tset)
> {
> + struct task_struct *task;
> struct io_context *ioc;
>
> - task_lock(tsk);
> - ioc = tsk->io_context;
> - if (ioc)
> - ioc->cgroup_changed = 1;
> - task_unlock(tsk);
> + cgroup_taskset_for_each(task, cgrp, tset) {
> + task_lock(task);
> + ioc = task->io_context;
> + if (ioc)
> + ioc->cgroup_changed = 1;
> + task_unlock(task);
> + }
> }
>
> void blkio_policy_register(struct blkio_policy_type *blkiop)
> diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
> index a2b0082..2cb5e72 100644
> --- a/kernel/cgroup_freezer.c
> +++ b/kernel/cgroup_freezer.c
> @@ -162,10 +162,14 @@ static int freezer_can_attach(struct cgroup_subsys *ss,
> struct cgroup_taskset *tset)
> {
> struct freezer *freezer;
> + struct task_struct *task;
>
> /*
> * Anything frozen can't move or be moved to/from.
> */
> + cgroup_taskset_for_each(task, new_cgroup, tset)
> + if (cgroup_freezing(task))
> + return -EBUSY;
>
> freezer = cgroup_freezer(new_cgroup);
> if (freezer->state != CGROUP_THAWED)
> @@ -174,11 +178,6 @@ static int freezer_can_attach(struct cgroup_subsys *ss,
> return 0;
> }
>
> -static int freezer_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
> -{
> - return cgroup_freezing(tsk) ? -EBUSY : 0;
> -}
> -
> static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
> {
> struct freezer *freezer;
> @@ -374,10 +373,5 @@ struct cgroup_subsys freezer_subsys = {
> .populate = freezer_populate,
> .subsys_id = freezer_subsys_id,
> .can_attach = freezer_can_attach,
> - .can_attach_task = freezer_can_attach_task,
> - .pre_attach = NULL,
> - .attach_task = NULL,
> - .attach = NULL,
> .fork = freezer_fork,
> - .exit = NULL,
> };
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index 2e5825b..472ddd6 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -1372,33 +1372,34 @@ static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
> struct cgroup_taskset *tset)
> {
> struct cpuset *cs = cgroup_cs(cgrp);
> + struct task_struct *task;
> + int ret;
>
> if (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
> return -ENOSPC;
>
> - /*
> - * Kthreads bound to specific cpus cannot be moved to a new cpuset; we
> - * cannot change their cpu affinity and isolating such threads by their
> - * set of allowed nodes is unnecessary. Thus, cpusets are not
> - * applicable for such threads. This prevents checking for success of
> - * set_cpus_allowed_ptr() on all attached tasks before cpus_allowed may
> - * be changed.
> - */
> - if (cgroup_taskset_first(tset)->flags & PF_THREAD_BOUND)
> - return -EINVAL;
> -
> + cgroup_taskset_for_each(task, cgrp, tset) {
> + /*
> + * Kthreads bound to specific cpus cannot be moved to a new
> + * cpuset; we cannot change their cpu affinity and
> + * isolating such threads by their set of allowed nodes is
> + * unnecessary. Thus, cpusets are not applicable for such
> + * threads. This prevents checking for success of
> + * set_cpus_allowed_ptr() on all attached tasks before
> + * cpus_allowed may be changed.
> + */
> + if (task->flags & PF_THREAD_BOUND)
> + return -EINVAL;
> + if ((ret = security_task_setscheduler(task)))
> + return ret;
> + }
> return 0;
> }
>
> -static int cpuset_can_attach_task(struct cgroup *cgrp, struct task_struct *task)
> -{
> - return security_task_setscheduler(task);
> -}
> -
> /*
> * Protected by cgroup_lock. The nodemasks must be stored globally because
> * dynamically allocating them is not allowed in pre_attach, and they must
> - * persist among pre_attach, attach_task, and attach.
> + * persist among pre_attach, and attach.
> */
> static cpumask_var_t cpus_attach;
> static nodemask_t cpuset_attach_nodemask_from;
> @@ -1417,39 +1418,34 @@ static void cpuset_pre_attach(struct cgroup *cont)
> guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
> }
>
> -/* Per-thread attachment work. */
> -static void cpuset_attach_task(struct cgroup *cont, struct task_struct *tsk)
> -{
> - int err;
> - struct cpuset *cs = cgroup_cs(cont);
> -
> - /*
> - * can_attach beforehand should guarantee that this doesn't fail.
> - * TODO: have a better way to handle failure here
> - */
> - err = set_cpus_allowed_ptr(tsk, cpus_attach);
> - WARN_ON_ONCE(err);
> -
> - cpuset_change_task_nodemask(tsk, &cpuset_attach_nodemask_to);
> - cpuset_update_task_spread_flag(cs, tsk);
> -}
> -
> static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
> struct cgroup_taskset *tset)
> {
> struct mm_struct *mm;
> - struct task_struct *tsk = cgroup_taskset_first(tset);
> + struct task_struct *task;
> + struct task_struct *leader = cgroup_taskset_first(tset);
> struct cgroup *oldcgrp = cgroup_taskset_cur_cgroup(tset);
> struct cpuset *cs = cgroup_cs(cgrp);
> struct cpuset *oldcs = cgroup_cs(oldcgrp);
>
> + cgroup_taskset_for_each(task, cgrp, tset) {
> + /*
> + * can_attach beforehand should guarantee that this doesn't
> + * fail. TODO: have a better way to handle failure here
> + */
> + WARN_ON_ONCE(set_cpus_allowed_ptr(task, cpus_attach));
> +
> + cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to);
> + cpuset_update_task_spread_flag(cs, task);
> + }
> +
> /*
> * Change mm, possibly for multiple threads in a threadgroup. This is
> * expensive and may sleep.
> */
> cpuset_attach_nodemask_from = oldcs->mems_allowed;
> cpuset_attach_nodemask_to = cs->mems_allowed;
> - mm = get_task_mm(tsk);
> + mm = get_task_mm(leader);
> if (mm) {
> mpol_rebind_mm(mm, &cpuset_attach_nodemask_to);
> if (is_memory_migrate(cs))
> @@ -1905,9 +1901,7 @@ struct cgroup_subsys cpuset_subsys = {
> .create = cpuset_create,
> .destroy = cpuset_destroy,
> .can_attach = cpuset_can_attach,
> - .can_attach_task = cpuset_can_attach_task,
> .pre_attach = cpuset_pre_attach,
> - .attach_task = cpuset_attach_task,
> .attach = cpuset_attach,
> .populate = cpuset_populate,
> .post_clone = cpuset_post_clone,
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index b8785e2..95e189d 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7000,10 +7000,13 @@ static int __perf_cgroup_move(void *info)
> return 0;
> }
>
> -static void
> -perf_cgroup_attach_task(struct cgroup *cgrp, struct task_struct *task)
> +static void perf_cgroup_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
> + struct cgroup_taskset *tset)
> {
> - task_function_call(task, __perf_cgroup_move, task);
> + struct task_struct *task;
> +
> + cgroup_taskset_for_each(task, cgrp, tset)
> + task_function_call(task, __perf_cgroup_move, task);
> }
>
> static void perf_cgroup_exit(struct cgroup_subsys *ss, struct cgroup *cgrp,
> @@ -7017,7 +7020,7 @@ static void perf_cgroup_exit(struct cgroup_subsys *ss, struct cgroup *cgrp,
> if (!(task->flags & PF_EXITING))
> return;
>
> - perf_cgroup_attach_task(cgrp, task);
> + task_function_call(task, __perf_cgroup_move, task);
> }
>
> struct cgroup_subsys perf_subsys = {
> @@ -7026,6 +7029,6 @@ struct cgroup_subsys perf_subsys = {
> .create = perf_cgroup_create,
> .destroy = perf_cgroup_destroy,
> .exit = perf_cgroup_exit,
> - .attach_task = perf_cgroup_attach_task,
> + .attach = perf_cgroup_attach,
> };
> #endif /* CONFIG_CGROUP_PERF */
> diff --git a/kernel/sched.c b/kernel/sched.c
> index ccacdbd..dd7e460 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -8966,24 +8966,31 @@ cpu_cgroup_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp)
> sched_destroy_group(tg);
> }
>
> -static int
> -cpu_cgroup_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
> +static int cpu_cgroup_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
> + struct cgroup_taskset *tset)
> {
> + struct task_struct *task;
> +
> + cgroup_taskset_for_each(task, cgrp, tset) {
> #ifdef CONFIG_RT_GROUP_SCHED
> - if (!sched_rt_can_attach(cgroup_tg(cgrp), tsk))
> - return -EINVAL;
> + if (!sched_rt_can_attach(cgroup_tg(cgrp), task))
> + return -EINVAL;
> #else
> - /* We don't support RT-tasks being in separate groups */
> - if (tsk->sched_class != &fair_sched_class)
> - return -EINVAL;
> + /* We don't support RT-tasks being in separate groups */
> + if (task->sched_class != &fair_sched_class)
> + return -EINVAL;
> #endif
> + }
> return 0;
> }
>
> -static void
> -cpu_cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
> +static void cpu_cgroup_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
> + struct cgroup_taskset *tset)
> {
> - sched_move_task(tsk);
> + struct task_struct *task;
> +
> + cgroup_taskset_for_each(task, cgrp, tset)
> + sched_move_task(task);
> }
>
> static void
> @@ -9071,8 +9078,8 @@ struct cgroup_subsys cpu_cgroup_subsys = {
> .name = "cpu",
> .create = cpu_cgroup_create,
> .destroy = cpu_cgroup_destroy,
> - .can_attach_task = cpu_cgroup_can_attach_task,
> - .attach_task = cpu_cgroup_attach_task,
> + .can_attach = cpu_cgroup_can_attach,
> + .attach = cpu_cgroup_attach,
> .exit = cpu_cgroup_exit,
> .populate = cpu_cgroup_populate,
> .subsys_id = cpu_cgroup_subsys_id,
> --
> 1.7.6
>
>
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