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Commit 07c41a29 authored by Yonghong Song's avatar Yonghong Song Committed by David S. Miller
Browse files

bpf: avoid rcu_dereference inside bpf_event_mutex lock region 



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: default avatarYonghong Song <yhs@fb.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarMartin KaFai Lau <kafai@fb.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 3051fbec

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);

}