CVE-2026-89580 bpf: Disable preemption in __bpf_get_stack

In the Linux kernel, the following vulnerability has been resolved: bpf: Disable preemption in bpfgetstack getperfcallchain returns a per-CPU perfcallchainentry buffer and releases its recursion slot via putcallchainentry before returning, so nothing keeps the entry reserved while bpfgetstack...