On Tue, Mar 23, 2010 at 09:18:43PM +0000, Russell King - ARM Linux wrote:
<snip> (sorry -- I'm not familiar with ARM so I can't respond to those)
> > +/* dump the thread_struct of a given task */
> > +int checkpoint_thread(struct ckpt_ctx *ctx, struct task_struct *t)
> > +{
> > + int ret;
> > + struct ckpt_hdr_thread *h;
> > + struct thread_info *ti = task_thread_info(t);
> > +
> > + h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_THREAD);
> > + if (!h)
> > + return -ENOMEM;
> > +
> > + /*
> > + * Store the syscall information about the checkpointed process
> > + * as we need to know if the process was doing a syscall (and which)
> > + * during restart.
> > + */
> > + h->syscall = ti->syscall;
> > +
> > + /*
> > + * Store remaining thread-specific info.
> > + */
> > + h->tp_value = ti->tp_value;
>
> How do you safely obtain consistent information from a thread? Do you
> temporarily stop it?
It must be frozen with the cgroup freezer (which reuses the suspend freezer).
sys_checkpoint moves the cgroup freezer into the CHECKPOINTING state which
prevents tasks in that group from being thawed until just before checkpoint
returns.
Cheers,
-Matt Helsley
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