linux-kernel - [PATCH net-next v5 2/4] net: devmem: refactor sock_devmem

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Message-Id: <20251023-scratch-bobbyeshleman-devmem-tcp-token-upstream-v5-2-47cb85f5259e@meta.com>
Date: Thu, 23 Oct 2025 13:58:21 -0700
From: Bobby Eshleman <bobbyeshleman@...il.com>
To: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 Kuniyuki Iwashima <kuniyu@...gle.com>, 
 Willem de Bruijn <willemb@...gle.com>, Neal Cardwell <ncardwell@...gle.com>, 
 David Ahern <dsahern@...nel.org>, Mina Almasry <almasrymina@...gle.com>
Cc: Stanislav Fomichev <sdf@...ichev.me>, netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Bobby Eshleman <bobbyeshleman@...a.com>
Subject: [PATCH net-next v5 2/4] net: devmem: refactor sock_devmem_dontneed
 for autorelease split

From: Bobby Eshleman <bobbyeshleman@...a.com>

Refactor sock_devmem_dontneed() in preparation for supporting both
autorelease and manual token release modes.

Split the function into two parts:
- sock_devmem_dontneed(): handles input validation, token allocation,
  and copying from userspace
- sock_devmem_dontneed_autorelease(): performs the actual token release
  via xarray lookup and page pool put

This separation allows a future commit to add a parallel
sock_devmem_dontneed_manual_release() function that uses a different
token tracking mechanism (per-niov reference counting) without
duplicating the input validation logic.

The refactoring is purely mechanical with no functional change. Only
intended to minimize the noise in subsequent patches.

Signed-off-by: Bobby Eshleman <bobbyeshleman@...a.com>
---
 net/core/sock.c | 52 ++++++++++++++++++++++++++++++++--------------------
 1 file changed, 32 insertions(+), 20 deletions(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index a99132cc0965..e7b378753763 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1082,30 +1082,13 @@ static int sock_reserve_memory(struct sock *sk, int bytes)
 #define MAX_DONTNEED_FRAGS 1024

 static noinline_for_stack int
-sock_devmem_dontneed(struct sock *sk, sockptr_t optval, unsigned int optlen)
+sock_devmem_dontneed_autorelease(struct sock *sk, struct dmabuf_token *tokens,
+				 unsigned int num_tokens)
 {
-	unsigned int num_tokens, i, j, k, netmem_num = 0;
-	struct dmabuf_token *tokens;
+	unsigned int i, j, k, netmem_num = 0;
 	int ret = 0, num_frags = 0;
 	netmem_ref netmems[16];

-	if (!sk_is_tcp(sk))
-		return -EBADF;
-
-	if (optlen % sizeof(*tokens) ||
-	    optlen > sizeof(*tokens) * MAX_DONTNEED_TOKENS)
-		return -EINVAL;
-
-	num_tokens = optlen / sizeof(*tokens);
-	tokens = kvmalloc_array(num_tokens, sizeof(*tokens), GFP_KERNEL);
-	if (!tokens)
-		return -ENOMEM;
-
-	if (copy_from_sockptr(tokens, optval, optlen)) {
-		kvfree(tokens);
-		return -EFAULT;
-	}
-
 	xa_lock_bh(&sk->sk_user_frags);
 	for (i = 0; i < num_tokens; i++) {
 		for (j = 0; j < tokens[i].token_count; j++) {
@@ -1135,6 +1118,35 @@ sock_devmem_dontneed(struct sock *sk, sockptr_t optval, unsigned int optlen)
 	for (k = 0; k < netmem_num; k++)
 		WARN_ON_ONCE(!napi_pp_put_page(netmems[k]));

+	return ret;
+}
+
+static noinline_for_stack int
+sock_devmem_dontneed(struct sock *sk, sockptr_t optval, unsigned int optlen)
+{
+	struct dmabuf_token *tokens;
+	unsigned int num_tokens;
+	int ret;
+
+	if (!sk_is_tcp(sk))
+		return -EBADF;
+
+	if (optlen % sizeof(*tokens) ||
+	    optlen > sizeof(*tokens) * MAX_DONTNEED_TOKENS)
+		return -EINVAL;
+
+	num_tokens = optlen / sizeof(*tokens);
+	tokens = kvmalloc_array(num_tokens, sizeof(*tokens), GFP_KERNEL);
+	if (!tokens)
+		return -ENOMEM;
+
+	if (copy_from_sockptr(tokens, optval, optlen)) {
+		kvfree(tokens);
+		return -EFAULT;
+	}
+
+	ret = sock_devmem_dontneed_autorelease(sk, tokens, num_tokens);
+
 	kvfree(tokens);
 	return ret;
 }

-- 
2.47.3