Patch "bpf, sockmap: On receive programs try to fast track SK_PASS ingress" has been added to the 5.9-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    bpf, sockmap: On receive programs try to fast track SK_PASS ingress

to the 5.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bpf-sockmap-on-receive-programs-try-to-fast-track-sk.patch
and it can be found in the queue-5.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 1699f9d7542306045797e4c7de90cf7b7f704e81
Author: John Fastabend <john.fastabend@xxxxxxxxx>
Date:   Fri Oct 9 11:36:37 2020 -0700

    bpf, sockmap: On receive programs try to fast track SK_PASS ingress
    
    [ Upstream commit 9ecbfb06a078c4911fb444203e8e41d93d22f886 ]
    
    When we receive an skb and the ingress skb verdict program returns
    SK_PASS we currently set the ingress flag and put it on the workqueue
    so it can be turned into a sk_msg and put on the sk_msg ingress queue.
    Then finally telling userspace with data_ready hook.
    
    Here we observe that if the workqueue is empty then we can try to
    convert into a sk_msg type and call data_ready directly without
    bouncing through a workqueue. Its a common pattern to have a recv
    verdict program for visibility that always returns SK_PASS. In this
    case unless there is an ENOMEM error or we overrun the socket we
    can avoid the workqueue completely only using it when we fall back
    to error cases caused by memory pressure.
    
    By doing this we eliminate another case where data may be dropped
    if errors occur on memory limits in workqueue.
    
    Fixes: 51199405f9672 ("bpf: skb_verdict, support SK_PASS on RX BPF path")
    Signed-off-by: John Fastabend <john.fastabend@xxxxxxxxx>
    Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
    Link: https://lore.kernel.org/bpf/160226859704.5692.12929678876744977669.stgit@john-Precision-5820-Tower
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index aa78784292a7e..eaf9c90389517 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -764,6 +764,7 @@ static void sk_psock_verdict_apply(struct sk_psock *psock,
 {
 	struct tcp_skb_cb *tcp;
 	struct sock *sk_other;
+	int err = -EIO;
 
 	switch (verdict) {
 	case __SK_PASS:
@@ -775,8 +776,20 @@ static void sk_psock_verdict_apply(struct sk_psock *psock,
 
 		tcp = TCP_SKB_CB(skb);
 		tcp->bpf.flags |= BPF_F_INGRESS;
-		skb_queue_tail(&psock->ingress_skb, skb);
-		schedule_work(&psock->work);
+
+		/* If the queue is empty then we can submit directly
+		 * into the msg queue. If its not empty we have to
+		 * queue work otherwise we may get OOO data. Otherwise,
+		 * if sk_psock_skb_ingress errors will be handled by
+		 * retrying later from workqueue.
+		 */
+		if (skb_queue_empty(&psock->ingress_skb)) {
+			err = sk_psock_skb_ingress(psock, skb);
+		}
+		if (err < 0) {
+			skb_queue_tail(&psock->ingress_skb, skb);
+			schedule_work(&psock->work);
+		}
 		break;
 	case __SK_REDIRECT:
 		sk_psock_skb_redirect(skb);