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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: 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>
This commit is contained in:
Yonghong Song 2017-10-30 13:50:22 -07:00 committed by David S. Miller
parent 3051fbec20
commit 07c41a295c
1 changed files with 7 additions and 10 deletions
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17
kernel/trace/bpf_trace.c
View File

@ -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);
}