From: Roman Gushchin <guro@fb.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Roman Gushchin <guroan@gmail.com>, Tejun Heo <tj@kernel.org>,
"cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Kernel Team <Kernel-team@fb.com>
Subject: Re: [PATCH v2 3/6] cgroup: cgroup v2 freezer
Date: Wed, 14 Nov 2018 17:06:06 +0000 [thread overview]
Message-ID: <20181114170558.GA24889@castle.DHCP.thefacebook.com> (raw)
In-Reply-To: <20181114165631.GE13885@redhat.com>
On Wed, Nov 14, 2018 at 05:56:32PM +0100, Oleg Nesterov wrote:
> Hi Roman,
>
> On 11/13, Roman Gushchin wrote:
> >
> > > > +#define TASK_FROZEN 0x1000
> > > > +#define TASK_STATE_MAX 0x2000
> > >
> > > Just noticed the new task state... Why? Can't we avoid it?
> >
> > We can, but it's nice to show to userspace that tasks are frozen,
> > rather than just stuck somewhere in the kernel...
>
> But then you need to change get_task_state() too. Which iiuc could
> probably check ->frozen along with ->state.
>
> I do not think the new task state is a good idea, at least I would like
> to ask you to make a separate patch which we can discuss separately.
Yeah, I have separated it in v3.
>
>
> > > > + set_current_state(TASK_WAKEKILL | TASK_INTERRUPTIBLE | TASK_FROZEN);
> > >
> > > Why not __set_current_state() ?
> >
> > Hm, it's not a hot path at all, so set_current_state() is good enough.
> > Not a strong preference, of course.
>
> It is not about performance, to me set_current_state() looks as if we need
> a memory barrier for some obscure/undocumented reason and this doesn't help
> to understand the code.
>
> > > If ->state include TASK_INTERRUPTIBLE, why do we need TASK_WAKEKILL?
> > >
> > > And again, why TASK_FROZEN?
> >
> > So, should it be just TASK_INTERRUPTIBLE | TASK_FROZEN ?
>
> Again, TASK_FROZEN is pointless at least until you change fs/proc or until
> you have wake_up_state(TASK_FROZEN). May be cgroup_do_freeze() and/or
> ptrace_attach() could use it, but see above, I'd suggest to make another
> patch.
>
> Looks like you need TASK_KILLABLE, see below.
>
> > > > + clear_thread_flag(TIF_SIGPENDING);
> > > > + schedule();
> > > > + recalc_sigpending();
> > >
> > > I simply can't understand these 3 lines above but I bet this is not correct ;)
> >
> > So, yeah, the problem is that if there is TIF_SIGPENDING bit set, schedule()
> > will return immediately, so we're getting pretty much a busy loop here.
>
> I suspected this answer ;)
>
> > This is a nasty workaround.
>
> No, this is very wrong. Just suppose the caller is killed right before
> clear_thread_flag(TIF_SIGPENDING).
So, I had TASK_KILLABLE before, but had some issues with ptrace/gdb.
I'll revisit this option.
>
> > I believe we can clear and not call recalc_sigpending() at all. Does this seem
> > to be correct?
>
> I think you need to simply remove both clear_thread_flag() and recalc_sigpending().
> If schedule() is called in TASK_KILLABLE state it will return only if
> fatal_signal_pending() is true, and this is what we want, right?
>
> OK, it seems you are going to make the new version anyway, so I can wait for it
> and not read this series ;)
Sure! I'm about to post it.
Thanks!
next prev parent reply other threads:[~2018-11-14 17:06 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
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 [this message]
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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