[bpf-next,v2,3/4] bpf: Use rcu_trace_implies_rcu_gp() in local storage map

Commit Message

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

From: Hou Tao <[e-mail]>

Local storage map is accessible for both sleepable and non-sleepable bpf
program, and its memory is freed by using both call_rcu_tasks_trace() and
kfree_rcu() to wait for both RCU-tasks-trace grace period and RCU grace
period to pass.

With the introduction of rcu_trace_implies_rcu_gp(), both
bpf_selem_free_rcu() and bpf_local_storage_free_rcu() 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 call kfree()
directly.

Signed-off-by: Hou Tao <[e-mail]>
---
 kernel/bpf/bpf_local_storage.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

Patch

diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
index 802fc15b0d73..9dc6de1cf185 100644
--- a/kernel/bpf/bpf_local_storage.c
+++ b/kernel/bpf/bpf_local_storage.c
@@ -88,8 +88,14 @@  void bpf_local_storage_free_rcu(struct rcu_head *rcu)
 {
 	struct bpf_local_storage *local_storage;
 
+	/* If RCU Tasks Trace grace period implies RCU grace period, do
+	 * kfree(), else do kfree_rcu().
+	 */
 	local_storage = container_of(rcu, struct bpf_local_storage, rcu);
-	kfree_rcu(local_storage, rcu);
+	if (rcu_trace_implies_rcu_gp())
+		kfree(local_storage);
+	else
+		kfree_rcu(local_storage, rcu);
 }
 
 static void bpf_selem_free_rcu(struct rcu_head *rcu)
@@ -97,7 +103,10 @@  static void bpf_selem_free_rcu(struct rcu_head *rcu)
 	struct bpf_local_storage_elem *selem;
 
 	selem = container_of(rcu, struct bpf_local_storage_elem, rcu);
-	kfree_rcu(selem, rcu);
+	if (rcu_trace_implies_rcu_gp())
+		kfree(selem);
+	else
+		kfree_rcu(selem, rcu);
 }
 
 /* local_storage->lock must be held and selem->local_storage == local_storage.