[bpf-next,v2,4/4] bpf: Use rcu_trace_implies_rcu_gp() for program array freeing

Commit Message

Hou Tao Oct. 14, 2022, 11:39 a.m. UTC

From: Hou Tao <[e-mail]>

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 <[e-mail]>
---
 kernel/bpf/core.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

Patch

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 711fd293b6de..4bc5f46d7030 100644
--- 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)