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SubjectRe: [RFC v17][PATCH 22/60] c/r: external checkpoint of a task other than ourself


Serge E. Hallyn wrote:
> Quoting Oren Laadan (orenl@librato.com):
>> Now we can do "external" checkpoint, i.e. act on another task.
>
> ...
>
>> long do_checkpoint(struct ckpt_ctx *ctx, pid_t pid)
>> {
>> long ret;
>>
>> + ret = init_checkpoint_ctx(ctx, pid);
>> + if (ret < 0)
>> + return ret;
>> +
>> + if (ctx->root_freezer) {
>> + ret = cgroup_freezer_begin_checkpoint(ctx->root_freezer);
>> + if (ret < 0)
>> + return ret;
>> + }
>
> Self-checkpoint of a task in root freezer is now denied, though.
>
> Was that intentional?

Yes.

"root freezer" is an arbitrary task in the checkpoint subtree or
container. It is used to verify that all checkpointed tasks - except
for current, if doing self-checkpoint - belong to the same freezer
group.

Since current is busy calling checkpoint(2), and since we only permit
checkpoint of (cgroup-) frozen tasks, then - by definition - it cannot
possibly belong to the same group. If it did, it would itself be frozen
like its fellows and unable to call checkpoint(2).

Oren.



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