Serge E. Hallyn wrote:
> Quoting Oren Laadan (or...@cs.columbia.edu):
>>> /* dump the task_struct of a given task */
>>> static int checkpoint_task_struct(struct ckpt_ctx *ctx, struct task_struct
>>> *t)
>>> {
>>> struct ckpt_hdr_task *h;
>>> int ret;
>>> + int realcred_ref, ecred_ref;
>>> +
>>> + realcred_ref = checkpoint_obj(ctx, t->real_cred, CKPT_OBJ_CRED);
>>> + if (realcred_ref < 0)
>>> + return realcred_ref;
>>> +
>>> + ecred_ref = checkpoint_obj(ctx, t->cred, CKPT_OBJ_CRED);
>>> + if (ecred_ref < 0)
>>> + return ecred_ref;
>> Is this safe even if the checkpointed task's state changes ?
>> (e.g. unfrozen - yes, I know there is a patch in the works to
>> prevent this; but if we ever want to checkpoint STOPPED tasks...
>> for instance).
>>
>> Would incrementing the refcount on t->{cred,real_cred} help ?
>
> Doesn't checkpoint_obj already do that through obj_new?
>
No, it does not. There is a (potentially long) window of opportunity
between the callback invoked from checkpoint_obj() - where the pointer
is used, and when checkpoint_obj() later takes the extra reference.
See for comparison checkpoint_mm_obj(), it safely grabs the task->mm
(with a reference) around the invocation of checkpoint_obj().
Oren.
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