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

Nathan Lynch ntl at pobox.com
Mon May 18 16:21:22 PDT 2009

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().
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