[PATCH net-next] bpf: avoid rcu_dereference inside bpf_event_mutex lock region
From: Yonghong Song <hidden>
Date: 2017-10-30 20:50:26
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 <redacted>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <redacted>
---
kernel/trace/bpf_trace.c | 17 +++++++----------
1 file changed, 7 insertions(+), 10 deletions(-)
Peter,
Could you check whether the below change to remove rcu_dereference_protected
is what you wanted or not?
Thanks!
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index b65011d..e7685c5 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c@@ -767,20 +767,19 @@ 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; }
@@ -794,11 +793,9 @@ 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);
@@ -810,6 +807,6 @@ 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); }
--
2.9.5