linux-kernel - Re: [RFC v17][PATCH 22/60] c/r: external checkpoint of a task other than ourself

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Message-ID: <20090723145438.GA12945@us.ibm.com>
Date:	Thu, 23 Jul 2009 09:54:38 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Oren Laadan <orenl@...rato.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...l.org>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-api@...r.kernel.org, Dave Hansen <dave@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Oren Laadan <orenl@...columbia.edu>
Subject: Re: [RFC v17][PATCH 22/60] c/r: external checkpoint of a task
	other than ourself

Quoting Oren Laadan (orenl@...rato.com):
> 
> 
> Serge E. Hallyn wrote:
> > Quoting Oren Laadan (orenl@...rato.com):
> >> 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).
> 
> Oren.

Ok, well I don't know what was happening yesterday.  Today it's
restart that is failing, and as you pointed out on irc that's
on s390 only.  I'll send out a patch this afternoon to fix that.

Yesterday I must not have read the output right I guess...

thanks,
-serge
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