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Date:   Thu, 28 May 2020 21:26:20 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     KP Singh <kpsingh@...omium.org>
Cc:     davem@...emloft.net, daniel@...earbox.net, netdev@...r.kernel.org,
        bpf@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH bpf-next 1/3] bpf: Introduce sleepable BPF programs

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

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