Re: [PATCH net-next 2/3] bpf: permit multiple bpf attachments for a single perf event
From: Daniel Borkmann <daniel@iogearbox.net>
Date: 2017-10-23 20:52:48
On 10/23/2017 07:58 PM, Yonghong Song wrote: [...]
quoted hunk ↗ jump to hunk
__this_cpu_dec(bpf_prog_active);@@ -741,3 +754,63 @@ const struct bpf_verifier_ops perf_event_verifier_ops = { const struct bpf_prog_ops perf_event_prog_ops = { }; + +static DEFINE_MUTEX(bpf_event_mutex); + +int perf_event_attach_bpf_prog(struct perf_event *event, + struct bpf_prog *prog) +{ + struct bpf_prog_array __rcu *old_array; + struct bpf_prog_array *new_array; + int ret; + + mutex_lock(&bpf_event_mutex); + + if (event->prog) + return -EEXIST;
Needs to go to out here, otherwise deadlock.
+
+ old_array = rcu_dereference_protected(event->tp_event->prog_array,
+ lockdep_is_held(&bpf_event_mutex));
+ ret = bpf_prog_array_copy(old_array, NULL, prog, &new_array);
+ if (ret < 0)
+ goto out;
+
+ /* set the new array to event->tp_event and set event->prog */
+ event->prog = prog;
+ rcu_assign_pointer(event->tp_event->prog_array, new_array);
+
+ if (old_array)
+ bpf_prog_array_free(old_array);
+
+out:
+ mutex_unlock(&bpf_event_mutex);
+ return ret;
+}
+
+void perf_event_detach_bpf_prog(struct perf_event *event)
+{
+ struct bpf_prog_array __rcu *old_array;
+ struct bpf_prog_array *new_array;
+ int ret;
+
+ mutex_lock(&bpf_event_mutex);
+
+ if (!event->prog)
+ return;Ditto.
+
+ old_array = rcu_dereference_protected(event->tp_event->prog_array,
+ lockdep_is_held(&bpf_event_mutex));
+
+ ret = bpf_prog_array_copy(old_array, event->prog, NULL, &new_array);
+ if (ret < 0) {
+ bpf_prog_array_delete_safe(old_array, event->prog);
+ } else {
+ rcu_assign_pointer(event->tp_event->prog_array, new_array);
+ bpf_prog_array_free(old_array);
+ }
+
+ bpf_prog_put(event->prog);
+ event->prog = NULL;
+
+ mutex_unlock(&bpf_event_mutex);
+}[...]