bpf: avoid rcu_dereference inside bpf_event_mutex lock region (07c41a29) · Commits · 戴 / test

During perf event attaching/detaching bpf programs, the tp_event->prog_array change is protected by the bpf_event_mutex lock in both attaching and deteching functions. Although tp_event->prog_array is a rcu pointer, rcu_derefrence is not needed to access it since mutex lock will guarantee ordering. Verified through "make C=2" that sparse locking check still happy with the new change. Also change the label name in perf_event_{attach,detach}_bpf_prog from "out" to "unlock" to reflect the code action after the label. Signed-off-by:

Yonghong Song <yhs@fb.com> Acked-by:

Alexei Starovoitov <ast@kernel.org> Acked-by:

Martin KaFai Lau <kafai@fb.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

kernel/trace/bpf_trace.c

+7 −10

Original line number	Diff line number	Diff line
		@@ -769,20 +769,19 @@ int perf_event_attach_bpf_prog(struct perf_event *event,
		mutex_lock(&bpf_event_mutex);

		if (event->prog)
		goto out;
		goto unlock;

		old_array = rcu_dereference_protected(event->tp_event->prog_array,
		lockdep_is_held(&bpf_event_mutex));
		old_array = event->tp_event->prog_array;
		ret = bpf_prog_array_copy(old_array, NULL, prog, &new_array);
		if (ret < 0)
		goto out;
		goto unlock;

		/* 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);
		bpf_prog_array_free(old_array);

		out:
		unlock:
		mutex_unlock(&bpf_event_mutex);
		return ret;
		}
		@@ -796,11 +795,9 @@ void perf_event_detach_bpf_prog(struct perf_event *event)
		mutex_lock(&bpf_event_mutex);

		if (!event->prog)
		goto out;

		old_array = rcu_dereference_protected(event->tp_event->prog_array,
		lockdep_is_held(&bpf_event_mutex));
		goto unlock;

		old_array = event->tp_event->prog_array;
		ret = bpf_prog_array_copy(old_array, event->prog, NULL, &new_array);
		if (ret < 0) {
		bpf_prog_array_delete_safe(old_array, event->prog);
		@@ -812,6 +809,6 @@ void perf_event_detach_bpf_prog(struct perf_event *event)
		bpf_prog_put(event->prog);
		event->prog = NULL;

		out:
		unlock:
		mutex_unlock(&bpf_event_mutex);
		}

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