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: Wed, 30 Jan 2019 17:52:01 +0100 [thread overview]
Message-ID: <20190130165200.GA4131@redhat.com> (raw)
In-Reply-To: <CALo0P13XnGiFykMXY3ZKu158ZqnBwHru0gyhQUrJSHEprnmiHQ@mail.gmail.com>
Hi Roman,
On 01/28, Roman Gushchin wrote:
>
> Yes, I think you're right: cgroup_exit() should check CGRP_FREEZE bit,
> not CGRP_FROZEN. Like cgroup_post_fork() does (a one-liner change below).
but this won't fix all problems? it seems that you missed my other concerns.
Firstly, this doesn't look consistent. Suppose a cgroup contains a single
process sleeping in ptrace_stop(). Then it becomes CGRP_FROZEN right after
"echo 1 > cgroup.freeze".
OTOH. if this single task sleeps in do_freezer_trap() and gets PTRACE_INTERRUPT,
it will equally sleep ptrace_stop() but cgroup won't be CGRP_FROZEN. Never.
Worse, this looks just wrong. In the latter case, cgroup becomes CGRP_FROZEN
right after a 2nd task migrates to this cgroup, before this new task calls
do_freezer_trap() or cgroup_enter_stopped().
> About spurious transitions (like frozen->non frozen->frozen on a task
> being SIGKILLed):
> in early versions of the patchset I've tried to avoid them, but then
> following the Tejun's advice
> switched over to expose them to a user. The logic behind is simple: if
> the state of the cgroup has been changed (a task is gone, for
> example), let's notify a user.
OK, I won't argue...
actually I can't argue because I do not really understand why do we want
a "killable" freezer, let alone ptraceable ;)
Oleg.
next prev parent reply other threads:[~2019-01-30 16:52 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 [this message]
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
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