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

Oren Laadan orenl at cs.columbia.edu
Tue May 19 22:30:06 PDT 2009

Matt Helsley wrote:
> 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.

Allowing checkpoint of stopped tasks is actually not such a bad
idea, IMHO.

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