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)

quoted

+/* 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