Quoting Sukadev Bhattiprolu (sukadev@xxxxxxxxxxxxxxxxxx):
Bear with me as I try to get this straight...
Let's say we have the following task being checkpointed (btw, the
actual checkpoint code hopefully will, as Oren mentioned, not
be always checkpointing all of a task's pids, but only the
pids from the checkpointer's pidns level an up - but that doesn't
matter to you):
Either:
level no | pid
0 1001
1 50
2 3
or
level no | pid
0 1001
1 50
2 1
Now we want to restart that inside a container. So for the
first task we have a parent task:
level no | pid
0 5009
1 1000
2 49
3 2
calling clone_with_pid with upids {1001,50,3} to produce task:
level no | pid
0 5010
1 1001
2 50
3 3
So the numbers in your code for this case become:
> + unum_pids = pid_set.num_pids;
unum_pids = 3
> + knum_pids = task_pid(current)->level + 1;
knum_pids = 3 + 1 = 4
> + target_pids = kzalloc((knum_pids + 1) * sizeof(pid_t), GFP_KERNEL);
XXX First problem:
target_pids gets room for 5 pids, one more than we need.
> + j = knum_pids - unum_pids;
j = 1, so we copy the 3 pids in the right place.
> + rc = copy_from_user(&target_pids[j], pid_set.target_pids, size);
> + if (rc) {
> + rc = -EFAULT;
> + goto out_free;
> + }
> +
> + return target_pids;
For the second one, we have a parent task
level no | pid
0 5009
1 1000
2 49
calling clone_with_pid with CLONE_NEWPID and {1001,50,1} to produce:
level no | pid
0 5010
1 1001
2 50
3 1
So the numbers in your code become:
> + unum_pids = pid_set.num_pids;
unum_pids = 3
> + knum_pids = task_pid(current)->level + 1;
knum_pids = 2 + 1 = 3
> + target_pids = kzalloc((knum_pids + 1) * sizeof(pid_t), GFP_KERNEL);
target_pids gets room for 4 pids
> + j = knum_pids - unum_pids;
XXX Second problem:
j = 0, which is not right, should be 1?
> + rc = copy_from_user(&target_pids[j], pid_set.target_pids, size);
> + if (rc) {
> + rc = -EFAULT;
> + goto out_free;
> + }
> +
> + return target_pids;
So it looks like your usage of knum_pids isn't quite right.
(right?)
Or are you expecting userspace to not specify the 1, only 2
upids? In that case, you're requiring different behavior for
pid 1 than any others, which is kind of weird? Or is that just
me?
-serge
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