From: Oleg Nesterov <oleg@redhat.com>
To: Roman Gushchin <guroan@gmail.com>
Cc: Tejun Heo <tj@kernel.org>,
kernel-team@fb.com, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org, Roman Gushchin <guro@fb.com>
Subject: Re: [PATCH v6 4/7] cgroup: cgroup v2 freezer
Date: Fri, 25 Jan 2019 14:43:36 +0100 [thread overview]
Message-ID: <20190125134336.GA18991@redhat.com> (raw)
In-Reply-To: <20181222000307.28231-5-guro@fb.com>
On 12/21, Roman Gushchin wrote:
>
> +static void cgroup_do_freeze(struct cgroup *cgrp, bool freeze)
> +{
> + struct css_task_iter it;
> + struct task_struct *task;
> +
> + lockdep_assert_held(&cgroup_mutex);
> +
> + spin_lock_irq(&css_set_lock);
> + if (freeze) {
> + cgrp->freezer.nr_tasks_to_freeze = __cgroup_task_count(cgrp);
> + set_bit(CGRP_FREEZE, &cgrp->flags);
> + } else {
> + clear_bit(CGRP_FREEZE, &cgrp->flags);
> + }
> + spin_unlock_irq(&css_set_lock);
> +
> + css_task_iter_start(&cgrp->self, 0, &it);
> + while ((task = css_task_iter_next(&it))) {
> + /*
> + * Ignore kernel threads here. Freezing cgroups containing
> + * kthreads isn't supported.
> + */
> + if (task->flags & PF_KTHREAD)
> + continue;
> + cgroup_freeze_task(task, freeze);
> + }
> + css_task_iter_end(&it);
I don't understand why this can race with exiting task. Or with SIGKILL which
kills a task before it sets current->frozen.
How can we trust nr_tasks_to_freeze at all?
Yes you added cgroup_dec_tasks_to_freeze() into cgroup_exit(). But it won't be
called if CGRP_FROZEN was not set yet, or because of "spurious" transitions
caused by cgroup_inc/dec_frozen_cnt() called by this or other tasks.
it seems that cgroup_exit() should check CGRP_FREEZE instead...
Oleg.
next prev parent reply other threads:[~2019-01-25 13:43 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-22 0:03 [PATCH v6 0/7] freezer for cgroup v2 Roman Gushchin
2018-12-22 0:03 ` [PATCH v6 1/7] cgroup: rename freezer.c into legacy_freezer.c Roman Gushchin
2018-12-22 0:03 ` [PATCH v6 2/7] cgroup: implement __cgroup_task_count() helper Roman Gushchin
2018-12-22 0:03 ` [PATCH v6 3/7] cgroup: protect cgroup->nr_(dying_)descendants by css_set_lock Roman Gushchin
2018-12-22 0:03 ` [PATCH v6 4/7] cgroup: cgroup v2 freezer Roman Gushchin
2019-01-25 12:27 ` Oleg Nesterov
2019-01-25 13:46 ` Oleg Nesterov
2019-01-28 19:59 ` Roman Gushchin
2019-01-30 16:52 ` Oleg Nesterov
2019-02-11 21:30 ` Roman Gushchin
2019-02-14 16:26 ` Oleg Nesterov
2019-02-14 16:41 ` Roman Gushchin
2019-01-25 13:43 ` Oleg Nesterov [this message]
2018-12-22 0:03 ` [PATCH v6 5/7] kselftests: cgroup: don't fail on cg_kill_all() error in cg_destroy() Roman Gushchin
2018-12-22 0:03 ` [PATCH v6 6/7] kselftests: cgroup: add freezer controller self-tests Roman Gushchin
2018-12-22 0:03 ` [PATCH v6 7/7] cgroup: document cgroup v2 freezer interface Roman Gushchin
2019-01-24 15:26 ` [PATCH v6 0/7] freezer for cgroup v2 Tejun Heo
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