[Devel] Re: bugs with ckpt-v15-dev

[Matt Helsley]

On Mon, May 18, 2009 at 06:21:22PM -0500, Nathan Lynch wrote:
> Matt Helsley <matthltc at us.ibm.com> writes:
> 
> > On Mon, May 18, 2009 at 04:36:11PM -0500, Nathan Lynch wrote:
> >> 
> >> [1] Should CONFIG_CHECKPOINT depend on CONFIG_CGROUPS and/or
> >> CONFIG_CGROUPS_FREEZER?  We require tasks to be put in frozen state
> >> before checkpoint, is there any mechanism apart from
> >> cgroup/freezer.state to do this?
> >
> > Have you tried sending all of the tasks SIGSTOP? It won't 100% freeze
> > the tasks -- they'd still be capable of responding to some signals
> > (CONT, TERM..). Also they'd presumably be placed in the stopped state
> > upon restart so a SIGCONT will be needed. In the case of bash, at
> > least, that will technically change what happens upon restart. My
> > guess is that in many cases it won't matter but there are some where
> > it will.
> 
> Hmm, I'm having trouble understanding your suggestion.  The current
> checkpoint implementation requires non-self tasks to be frozen (p->flags
> & PF_FROZEN), which is not equivalent to stopped state (task->state &
> __TASK_STOPPED).  That is, it would refuse to checkpoint tasks in
> stopped state.  See may_checkpoint_task().

Oops. You're right. That would require changing may_checkpoint_task() to include
__TASK_STOPPED -- not something we'd want in the final code. I had assumed
you wanted to try a different mechanism for debugging purposes.

Cheers,
	-Matt Helsley
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