bpf: Fix UAF via mismatching bpf_prog/attachment RCU flavors

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

bpf: Fix UAF via mismatching bpf_prog/attachment RCU flavors

Uprobes always use bpf_prog_run_array_uprobe() under tasks-trace-RCU

protection. But it is possible to attach a non-sleepable BPF program to a

uprobe, and non-sleepable BPF programs are freed via normal RCU (see

__bpf_prog_put_noref()). This leads to UAF of the bpf_prog because a normal

RCU grace period does not imply a tasks-trace-RCU grace period.

Fix it by explicitly waiting for a tasks-trace-RCU grace period after

removing the attachment of a bpf_prog to a perf_event.