Re: [PATCH net-next 2/3] bpf: introduce BPF_MAP_TYPE_STACK_TRACE

From: Alexei Starovoitov
Date: Thu Feb 25 2016 - 11:43:56 EST

On 2/25/16 6:23 AM, Peter Zijlstra wrote:
+ id = hash & (smap->n_buckets - 1);
Its not at all clear where the corresponding rcu_read_lock() is at.

>+ bucket = rcu_dereference(smap->buckets[id]);

bpf programs of all types are always executing under rcu_read_lock().
This is fundamental for maps and majority of the helpers
that's why there is no WARN_ON(rcu_read_lock_held) in this helper,
since we already have it in many other places.
The rcu_read_lock() for kprobe type is in trace_call_bpf().