bpf: Allow sleepable programs to use tail calls

bpf: Allow sleepable programs to use tail calls

Allowing sleepable programs to use tail calls.

Making sure we can't mix sleepable and non-sleepable bpf programs
in tail call map (BPF_MAP_TYPE_PROG_ARRAY) and allowing it to be
used in sleepable programs.

Sleepable programs can be preempted and sleep which might bring
new source of race conditions, but both direct and indirect tail
calls should not be affected.

Direct tail calls work by patching direct jump to callee into bpf
caller program, so no problem there. We atomically switch from nop
to jump instruction.

Indirect tail call reads the callee from the map and then jumps to
it. The callee bpf program can't disappear (be released) from the
caller, because it is executed under rcu lock (rcu_read_lock_trace).

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/r/20260130081208.1130204-2-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>