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From: Tejun Heo <tj@kernel.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Roman Gushchin <guroan@gmail.com>,
	cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
	kernel-team@fb.com, Roman Gushchin <guro@fb.com>
Subject: Re: [PATCH v2 3/6] cgroup: cgroup v2 freezer
Date: Tue, 13 Nov 2018 07:43:49 -0800	[thread overview]
Message-ID: <20181113154349.GF2509588@devbig004.ftw2.facebook.com> (raw)
In-Reply-To: <20181113153700.GB30990@redhat.com>

Hello, Oleg.

On Tue, Nov 13, 2018 at 04:37:01PM +0100, Oleg Nesterov wrote:
> On 11/12, Roman Gushchin wrote:
> >
> > This patch implements freezer for cgroup v2. However the functionality
> > is similar, the interface is different to cgroup v1: it follows
> > cgroup v2 interface principles.
> 
> Oh, it seems that I actually need to apply this patch to (try to) understand
> the details ;) Will try tomorrow.

Yeah, it's a bit of a head spin like everything in signal delivery /
ptrace paths.

...
> OK, please forget for now, but perhaps it would be more clean to add
> JOBCTL_TRAP_FREEZE to the JOBCTL_PENDING_MASK check in recalc_sigpending()
> and change get_signal to check JOBCTL_TRAP_MASK | JOBCTL_TRAP_FREEZE; and
> I am not even sure cgroup_freezer_enter() should live in do_jobctl_trap().

I'm sure you're aware of the context but just to refresh - one thing
which was really broken about cgroup1 freezer was that it piggybacked
on hibernation freezer and put frozen tasks in a state which is
undefined when seen from userspace - they're just stuck in D sleep
somewhere in the kernel.  That's fine when the whole system is not
gonna be running, but not when only a subportion is being frozen.

So, the primary goal of cgroup2 freezer is putting the tasks in an
equivalent state as jobctl stop.  It's a jobctl stop but controlled by
cgroup frozen state, meaning that they can be killed, PTRACE_SEIZE'd
and INTERRUPT'ed (PTRACE_ATTACH doesn't work as signal delivery should
be blocked but that's fine) and so on.

Thanks.

-- 
tejun

  reply	other threads:[~2018-11-13 15:43 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-12 23:04 [PATCH v2 0/6] freezer for cgroup v2 Roman Gushchin
2018-11-12 23:04 ` [PATCH] cgroup: document cgroup v2 freezer interface Roman Gushchin
2018-11-12 23:04 ` [PATCH v2 1/6] cgroup: rename freezer.c into legacy_freezer.c Roman Gushchin
2018-11-12 23:04 ` [PATCH v2 2/6] cgroup: implement __cgroup_task_count() helper Roman Gushchin
2018-11-12 23:04 ` [PATCH v2 3/6] cgroup: cgroup v2 freezer Roman Gushchin
2018-11-13  2:08   ` Tejun Heo
2018-11-13 18:47     ` Roman Gushchin
2018-11-13 19:15       ` Tejun Heo
2018-11-13 20:55         ` Roman Gushchin
2018-11-13 20:58           ` Tejun Heo
2018-11-13 15:37   ` Oleg Nesterov
2018-11-13 15:43     ` Tejun Heo [this message]
2018-11-13 16:00       ` Oleg Nesterov
2018-11-13 15:48   ` Oleg Nesterov
2018-11-13 21:59     ` Roman Gushchin
2018-11-14 16:56       ` Oleg Nesterov
2018-11-14 17:06         ` Roman Gushchin
2018-11-14 17:36           ` Oleg Nesterov
2018-11-14 17:39             ` Roman Gushchin
2018-11-28 17:36         ` Roman Gushchin
2018-11-12 23:04 ` [PATCH v2 4/6] kselftests: cgroup: don't fail on cg_kill_all() error in cg_destroy() Roman Gushchin
2018-11-12 23:04 ` [PATCH v2 5/6] kselftests: cgroup: add freezer controller self-tests Roman Gushchin
2018-11-12 23:04 ` [PATCH v2 6/6] cgroup: document cgroup v2 freezer interface Roman Gushchin

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