[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20190130165200.GA4131@redhat.com>
Date: Wed, 30 Jan 2019 17:52:01 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Roman Gushchin <guroan@...il.com>
Cc: Tejun Heo <tj@...nel.org>, kernel-team@...com,
cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
Roman Gushchin <guro@...com>
Subject: Re: [PATCH v6 4/7] cgroup: cgroup v2 freezer
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.
Powered by blists - more mailing lists