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

[Serge E. Hallyn]

Quoting Oren Laadan (orenl at librato.com):
> 
> 
> Serge E. Hallyn wrote:
> > Quoting Oren Laadan (orenl at librato.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).

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
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