Re: [PATCH bpf-next 1/3] bpf: Introduce sleepable BPF programs

On Fri, May 29, 2020 at 12:12:27AM +0200, KP Singh wrote:

quoted

+			if (ret)
+				verbose(env, "%s() is not modifiable\n",
+					prog->aux->attach_func_name);
+		} else if (prog->aux->sleepable && prog->type == BPF_PROG_TYPE_TRACING) {
+			/* fentry/fexit progs can be sleepable only if they are
+			 * attached to ALLOW_ERROR_INJECTION or security_*() funcs.
+			 * LSM progs check that they are attached to bpf_lsm_*() funcs
+			 * which are sleepable too.

I know of one LSM hook which is not sleepable and is executed in an
RCU callback i.e. task_free. I don't think t's a problem to run under
SRCU for that (I tried it and it does not cause any issues).

We can add a blacklisting mechanism later for the sleepable flags or
just the sleeping helpers (based on some of the work going on to
whitelist functions for helper usage).

Good catch. *_task_free() are not sleepable. I'll introduce a simple
blacklist for now. Since I'm not adding actual sleeping helpers in this
patch set nothing is broken, but it will give us the base to build stuff on top.