AZL-66893

In the Linux kernel, the following vulnerability has been resolved:

rcu/nocb: Fix possible invalid rdp's->nocbcbkthread pointer access

In the preparation stage of CPU online, if the corresponding the rdp's->nocbcbkthread does not exist, will be created, there is a situation where the rdp's rcuop kthreads creation fails, and then de-offload this CPU's rdp, does not assign this CPU's rdp->nocbcbkthread pointer, but this rdp's->nocbgprdp and rdp's->rdpgp->nocbgp_kthread is still valid.

This will cause the subsequent re-offload operation of this offline CPU, which will pass the conditional check and the kthreadunpark() will access invalid rdp's->nocbcb_kthread pointer.

This commit therefore use rdp's->nocbgpkthread instead of rdpgp's->nocbgp_kthread for safety check.