FAILED: patch "[PATCH] tcp: call sk_wmem_schedule before sk_mem_charge in zerocopy" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 358ed624207012f03318235017ac6fb41f8af592 Mon Sep 17 00:00:00 2001
From: Talal Ahmad <[email protected]>
Date: Fri, 9 Jul 2021 11:43:06 -0400
Subject: [PATCH] tcp: call sk_wmem_schedule before sk_mem_charge in zerocopy
path

sk_wmem_schedule makes sure that sk_forward_alloc has enough bytes for charging that is going to be done by sk_mem_charge.

In the transmit zerocopy path, there is sk_mem_charge but there was no call to sk_wmem_schedule. This change adds that call.

Without this call to sk_wmem_schedule, sk_forward_alloc can go negetive which is a bug because sk_forward_alloc is a per-socket space that has been forward charged so this can't be negative.

index d5ab5f243640..8cb44040ec68 100644
@@ -1375,6 +1375,9 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 			}
 			pfrag->offset += copy;
 		} else {
+			if (!sk_wmem_schedule(sk, copy))
+				goto wait_for_space;
+
 			err = skb_zerocopy_iter_stream(sk, skb, msg, copy, uarg);
 			if (err == -EMSGSIZE || err == -EEXIST) {
 				tcp_mark_push(tp, skb);