From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
Subject: Re: [RFC v17][PATCH 22/60] c/r: external checkpoint of a task
	other than ourself
Date: Thu, 23 Jul 2009 08:12:50 -0500
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To: Oren Laadan <orenl-RdfvBDnrOixBDgjK7y7TUQ@public.gmane.org>
Cc: Alexey Dobriyan <adobriyan-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Dave Hansen <dave-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Linus Torvalds <torvalds-3NddpPZAyC0@public.gmane.org>, Alexander Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>, "H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org>, Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>
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Quoting Oren Laadan (orenl-RdfvBDnrOixBDgjK7y7TUQ@public.gmane.org):
> 
> 
> Serge E. Hallyn wrote:
> > Quoting Oren Laadan (orenl-RdfvBDnrOixBDgjK7y7TUQ@public.gmane.org):
> >> Now we can do "external" checkpoint, i.e. act on another task.
> > 
> > ...
> > 
> >>  long do_checkpoint(struct ckpt_ctx *ctx, pid_t pid)
> >>  {
> >>  	long ret;
> >>
> >> +	ret = init_checkpoint_ctx(ctx, pid);
> >> +	if (ret < 0)
> >> +		return ret;
> >> +
> >> +	if (ctx->root_freezer) {
> >> +		ret = cgroup_freezer_begin_checkpoint(ctx->root_freezer);
> >> +		if (ret < 0)
> >> +			return ret;
> >> +	}
> > 
> > Self-checkpoint of a task in root freezer is now denied, though.
> > 
> > Was that intentional?
> 
> Yes.
> 
> "root freezer" is an arbitrary task in the checkpoint subtree or
> container. It is used to verify that all checkpointed tasks - except
> for current, if doing self-checkpoint - belong to the same freezer
> group.
> 
> Since current is busy calling checkpoint(2), and since we only permit
> checkpoint of (cgroup-) frozen tasks, then - by definition - it cannot
> possibly belong to the same group. If it did, it would itself be frozen
> like its fellows and unable to call checkpoint(2).

So then you're saying that regular self-checkpoint no longer works,
but the documentation still shows self.c and claims it should just
work.

Mind you I prefer this as it is more consistent, but I thought it
was something you wanted to support.

-serge