Re: [PATCH bpf-next v11 2/6] bpf: Add bpf_prog_run_array_sleepable()

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Apr 21, 2026 at 01:42:25PM -0700, Alexei Starovoitov wrote:
> > +static __always_inline u32
> > +bpf_prog_run_array_sleepable(const struct bpf_prog_array *array,
> > +			     const void *ctx, bpf_prog_run_fn run_prog)
> > +{
> > +	const struct bpf_prog_array_item *item;
> > +	struct bpf_prog *prog;
> > +	struct bpf_run_ctx *old_run_ctx;
> > +	struct bpf_trace_run_ctx run_ctx;
> > +	u32 ret = 1;
> > +
> > +	might_fault();
> > +	RCU_LOCKDEP_WARN(!rcu_read_lock_trace_held(), "no rcu lock held");
> 
> The only caller of this function is in the next patch trace_call_bpf_faultable()
> that does 
> +	might_fault();
> +	guard(rcu_tasks_trace)();
> 
> imo above two lines are redunant.
> We can defensive programming when another caller appears.
> 
> > +
> > +	if (unlikely(!array))
> > +		return ret;
> > +
> > +	migrate_disable();
> > +
> > +	run_ctx.is_uprobe = false;
> > +
> > +	old_run_ctx = bpf_set_run_ctx(&run_ctx.run_ctx);
> > +	item = &array->items[0];
> > +	while ((prog = READ_ONCE(item->prog))) {
> > +		/* Skip dummy_bpf_prog placeholder (len == 0) */
> > +		if (unlikely(!prog->len)) {
> > +			item++;
> > +			continue;
> > +		}
> > +
> > +		if (!prog->sleepable)
> > +			rcu_read_lock();
> > +
> > +		if (unlikely(!bpf_prog_get_recursion_context(prog))) {
> > +			bpf_prog_inc_misses_counter(prog);
> > +			bpf_prog_put_recursion_context(prog);
> > +			if (!prog->sleepable)
> > +				rcu_read_unlock();
> 
> Why grab rcu_read_lock() and undo it?
> imo it would be cleaner and faster to do 
> bpf_prog_get_recursion_context() here ...
> 
> > +			item++;
> > +			continue;
> > +		}
> > +
> > +		run_ctx.bpf_cookie = item->bpf_cookie;
> > +		ret &= run_prog(prog, ctx);
> 
> ... and then here:
> if (!prog->sleepable) {
>   guard(rcu)();
>   ret &= run_prog(prog, ctx);
> } else {
>   ret &= run_prog(prog, ctx);
> }

Right, but the whole thing is called bpf_prog_run_array_sleepable(), why
are we doing silly things like this instead of hard assuming things
are sleepable and calling it a day?