bpf: Use rcu_trace_implies_rcu_gp() for program array freeing

To support both sleepable and normal uprobe bpf program, the freeing of
trace program array chains a RCU-tasks-trace grace period and a normal
RCU grace period one after the other.

With the introduction of rcu_trace_implies_rcu_gp(),
__bpf_prog_array_free_sleepable_cb() can check whether or not a normal
RCU grace period has also passed after a RCU-tasks-trace grace period
has passed. If it is true, it is safe to invoke kfree() directly.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20221014113946.965131-5-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 711fd29..4bc5f46 100644 (file)
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2251,8 +2251,14 @@ static void __bpf_prog_array_free_sleepable_cb(struct rcu_head *rcu)
 {
        struct bpf_prog_array *progs;
 
+       /* If RCU Tasks Trace grace period implies RCU grace period, there is
+        * no need to call kfree_rcu(), just call kfree() directly.
+        */
        progs = container_of(rcu, struct bpf_prog_array, rcu);
-       kfree_rcu(progs, rcu);
+       if (rcu_trace_implies_rcu_gp())
+               kfree(progs);
+       else
+               kfree_rcu(progs, rcu);
 }
 
 void bpf_prog_array_free_sleepable(struct bpf_prog_array *progs)