bpf: Add bpf_call_rcu_tasks_trace() kfunc
Sleepable BPF programs hold rcu_read_lock_trace(), not rcu_read_lock(), so a plain RCU grace period does not wait for them. A program whose readers are sleepable needs this flavour to defer reclaim safely. call_rcu_tasks_trace() is call_srcu() on rcu_tasks_trace_srcu_struct and SRCU invokes callbacks with BH disabled, so the callback is still not sleepable. It does run from a kworker rather than softirq or the rcuc/rcuo kthread, so a callback must not assume anything about current. Only the queueing call differs, so the two share struct bpf_rcu_head and all of the verifier plumbing. Signed-off-by: Puranjay Mohan <puranjay@kernel.org> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://patch.msgid.link/20260922200208.3203834-4-puranjay@kernel.org