bpf: Allow syscall bpf programs to call non-recur helpers

Allow syscall programs to call non-recur helpers too since syscall bpf
programs runs in process context through bpf syscall, BPF_PROG_TEST_RUN,
and cannot run recursively.

bpf_task_storage_{get,set} have "_recur" versions that call trylock
instead of taking the lock directly to avoid deadlock when called by
bpf programs that run recursively. Currently, only bpf_lsm, bpf_iter,
struct_ops without private stack are allow to call the non-recur helpers
since they cannot be recursively called in another bpf program.

Signed-off-by: Amery Hung <[e-mail]>
Reviewed-by: Emil Tsalapatis <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

include/linux/bpf_verifier.h

···
 	case BPF_PROG_TYPE_STRUCT_OPS:
 		return prog->aux->jits_use_priv_stack;
 	case BPF_PROG_TYPE_LSM:
+	case BPF_PROG_TYPE_SYSCALL:
 		return false;
 	default:
 		return true;