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 13:27:13 +0100 [thread overview]
Message-ID: <20190125122713.GA18218@redhat.com> (raw)
In-Reply-To: <20181222000307.28231-5-guro@fb.com>
Sorry, this version raced with my vacation, I missed it.
I'll try to read this code carefully but after a quick glance I have some
concerns,
On 12/21, Roman Gushchin wrote:
>
> +static void cgroup_update_frozen(struct cgroup *cgrp)
> +{
> + bool frozen;
> +
> + lockdep_assert_held(&css_set_lock);
> +
> + /*
> + * If the cgroup has to be frozen (CGRP_FREEZE bit set),
> + * and all tasks are frozen or stopped, let's consider
> + * the cgroup frozen. Otherwise it's not frozen.
> + */
> + frozen = test_bit(CGRP_FREEZE, &cgrp->flags) &&
> + cgrp->freezer.nr_frozen_tasks +
> + cgrp->freezer.nr_stopped_tasks ==
> + cgrp->freezer.nr_tasks_to_freeze;
OK. Suppose that cgroup is frozen, CGRP_FROZEN is set, stopped == 0,
to_freeze = frozen.
One of the task is killed, it calls leave_frozen(). If I read this code path
correctly, only ->nr_frozen_tasks will be decremented, so "frozen" will be
"false" when cgroup_update_frozen() is called.
Doesn't this mean that this cgroup will no longer be CGRP_FROZEN even after
the killed task goes away completely?
Or. Suppose that another process picks a task from the CGRP_FROZEN cgroup and
does PTRACE_ATTACH + PTRACE_INTERRUPT. IIUC, the tracee will only increment
->nr_stopped_tasks, it won't touch other counters. Again, cgroup won't be FROZEN
until PTRACE_CONT'ed tracee does cgroup_leave_stopped() ? This looks strange at
least.
SIGSTOP. IIUC, a frozen task sleeping in do_freezer_trap() won't stop. However if
another thread has already called do_signal_stop(), the woken frozen task will
react to JOBCTL_STOP_PENDING and stop. And do_signal_stop()->cgroup_enter_stopped()
will "destroy" CGRP_FROZEN too, or I am totally confused.
OTOH, if you freeze a TASK_STOPPED task's cgroup, this task can react to SIGCONT,
notify its parent, then freeze again. This is fine, but iiuc this cgroup won't be
FROZEN in between, cgroup_file_notify() will be called twice...
Oleg.
next prev parent reply other threads:[~2019-01-25 12:27 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 [this message]
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
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190125122713.GA18218@redhat.com \
--to=oleg@redhat.com \
--cc=cgroups@vger.kernel.org \
--cc=guro@fb.com \
--cc=guroan@gmail.com \
--cc=kernel-team@fb.com \
--cc=linux-kernel@vger.kernel.org \
--cc=tj@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).