df3225 uid 1001: building p_pptr cycle via procfs ctl attach
[main] A=856 B=855 C=854
[A 856] attaching B (855)
[A] running B
[B 855] attaching A (856) back -> cycle
[B] running A again
[main] B reported cycle complete
[main] go marker set; A enters ptrace walk
[A 856] ptrace(PT_ATTACH, 854): if vulnerable, never returns
[main] after 5s: kill -9 A (856)
[main] A SURVIVED SIGKILL -> stuck in kernel spin
[main] now kill -9 C (854): needs C.p_token held by spinning A -- expect HANG below (no further output)