[PATCH v5 net-next 1/2] net: tipc: fix FB_MTU eat two pages

[menglong8.dong@gmail.com]

From: Menglong Dong <dong.menglong@zte.com.cn>

FB_MTU is used in 'tipc_msg_build()' to alloc smaller skb when memory
allocation fails, which can avoid unnecessary sending failures.

The value of FB_MTU now is 3744, and the data size will be:

  (3744 + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) + \
    SKB_DATA_ALIGN(BUF_HEADROOM + BUF_TAILROOM + 3))

which is larger than one page(4096), and two pages will be allocated.

To avoid it, replace '3744' with a calculation:

  (PAGE_SIZE - SKB_DATA_ALIGN(BUF_OVERHEAD) - \
    SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))

What's more, alloc_skb_fclone() will call SKB_DATA_ALIGN for data size,
and it's not necessary to make alignment for buf_size in
tipc_buf_acquire(). So, just remove it.

Fixes: 4c94cc2d3d57 ("tipc: fall back to smaller MTU if allocation of local send skb fails")

Signed-off-by: Menglong Dong <dong.menglong@zte.com.cn>
Acked-by: Jon Maloy <jmaloy@redhat.com>
---
V5:
- remove ONE_PAGE_SKB_SZ and replace it with one_page_mtu

V4:
- fallback to V2

V3:
- split tipc_msg_build to tipc_msg_build and tipc_msg_frag
- introduce tipc_buf_acquire_flex, which is able to alloc skb for
  local message
- add the variate 'local' in tipc_msg_build to check if this is a
  local message.

V2:
- define FB_MTU in msg.c instead of introduce a new file
- remove align for buf_size in tipc_buf_acquire()
---
 net/tipc/bcast.c |  2 +-
 net/tipc/msg.c   | 17 ++++++++---------
 net/tipc/msg.h   |  3 ++-
 3 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/net/tipc/bcast.c b/net/tipc/bcast.c
index d4beca895992..593846d25214 100644
--- a/net/tipc/bcast.c
+++ b/net/tipc/bcast.c
@@ -699,7 +699,7 @@ int tipc_bcast_init(struct net *net)
 	spin_lock_init(&tipc_net(net)->bclock);
 
 	if (!tipc_link_bc_create(net, 0, 0, NULL,
-				 FB_MTU,
+				 one_page_mtu,
 				 BCLINK_WIN_DEFAULT,
 				 BCLINK_WIN_DEFAULT,
 				 0,
diff --git a/net/tipc/msg.c b/net/tipc/msg.c
index ce6ab54822d8..7053c22e393e 100644
--- a/net/tipc/msg.c
+++ b/net/tipc/msg.c
@@ -44,12 +44,15 @@
 #define MAX_FORWARD_SIZE 1024
 #ifdef CONFIG_TIPC_CRYPTO
 #define BUF_HEADROOM ALIGN(((LL_MAX_HEADER + 48) + EHDR_MAX_SIZE), 16)
-#define BUF_TAILROOM (TIPC_AES_GCM_TAG_SIZE)
+#define BUF_OVERHEAD (BUF_HEADROOM + TIPC_AES_GCM_TAG_SIZE)
 #else
 #define BUF_HEADROOM (LL_MAX_HEADER + 48)
-#define BUF_TAILROOM 16
+#define BUF_OVERHEAD BUF_HEADROOM
 #endif
 
+const int one_page_mtu = PAGE_SIZE - SKB_DATA_ALIGN(BUF_OVERHEAD) -
+			 SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+
 static unsigned int align(unsigned int i)
 {
 	return (i + 3) & ~3u;
@@ -69,13 +72,8 @@ static unsigned int align(unsigned int i)
 struct sk_buff *tipc_buf_acquire(u32 size, gfp_t gfp)
 {
 	struct sk_buff *skb;
-#ifdef CONFIG_TIPC_CRYPTO
-	unsigned int buf_size = (BUF_HEADROOM + size + BUF_TAILROOM + 3) & ~3u;
-#else
-	unsigned int buf_size = (BUF_HEADROOM + size + 3) & ~3u;
-#endif
 
-	skb = alloc_skb_fclone(buf_size, gfp);
+	skb = alloc_skb_fclone(BUF_OVERHEAD + size, gfp);
 	if (skb) {
 		skb_reserve(skb, BUF_HEADROOM);
 		skb_put(skb, size);
@@ -395,7 +393,8 @@ int tipc_msg_build(struct tipc_msg *mhdr, struct msghdr *m, int offset,
 		if (unlikely(!skb)) {
 			if (pktmax != MAX_MSG_SIZE)
 				return -ENOMEM;
-			rc = tipc_msg_build(mhdr, m, offset, dsz, FB_MTU, list);
+			rc = tipc_msg_build(mhdr, m, offset, dsz,
+					    one_page_mtu, list);
 			if (rc != dsz)
 				return rc;
 			if (tipc_msg_assemble(list))
diff --git a/net/tipc/msg.h b/net/tipc/msg.h
index 5d64596ba987..64ae4c4c44f8 100644
--- a/net/tipc/msg.h
+++ b/net/tipc/msg.h
@@ -99,9 +99,10 @@ struct plist;
 #define MAX_H_SIZE                60	/* Largest possible TIPC header size */
 
 #define MAX_MSG_SIZE (MAX_H_SIZE + TIPC_MAX_USER_MSG_SIZE)
-#define FB_MTU                  3744
 #define TIPC_MEDIA_INFO_OFFSET	5
 
+extern const int one_page_mtu;
+
 struct tipc_skb_cb {
 	union {
 		struct {
-- 
2.32.0