[PATCH v2 net-next 1/2] net: tipc: fix FB_MTU eat two pages

[menglong8 . dong]

From: Menglong Dong <dong.menglong@xxxxxxxxxx>

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:

FB_MTU = (PAGE_SIZE - SKB_DATA_ALIGN(sizeof(struct skb_shared_info))
          - SKB_DATA_ALIGN(BUF_HEADROOM + BUF_TAILROOM))

What's more, alloc_skb_fclone() will call SKB_DATA_ALIGN for data size,
and it's not unnecessary 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")

Reported-by: Zeal Robot <zealci@xxxxxxxxxx>
Signed-off-by: Menglong Dong <dong.menglong@xxxxxxxxxx>
---
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   | 15 ++++++++-------
 net/tipc/msg.h   |  3 ++-
 3 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/net/tipc/bcast.c b/net/tipc/bcast.c
index d4beca895992..9daace9542f4 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,
+				 fb_mtu,
 				 BCLINK_WIN_DEFAULT,
 				 BCLINK_WIN_DEFAULT,
 				 0,
diff --git a/net/tipc/msg.c b/net/tipc/msg.c
index ce6ab54822d8..a5c030ca7065 100644
--- a/net/tipc/msg.c
+++ b/net/tipc/msg.c
@@ -47,8 +47,14 @@
 #define BUF_TAILROOM (TIPC_AES_GCM_TAG_SIZE)
 #else
 #define BUF_HEADROOM (LL_MAX_HEADER + 48)
-#define BUF_TAILROOM 16
+#define BUF_TAILROOM 0
 #endif
+#define FB_MTU (PAGE_SIZE - \
+		SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) - \
+		SKB_DATA_ALIGN(BUF_HEADROOM + BUF_TAILROOM) \
+		)
+
+const int fb_mtu = FB_MTU;
 
 static unsigned int align(unsigned int i)
 {
@@ -69,13 +75,8 @@ 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_HEADROOM + size + BUF_TAILROOM, gfp);
 	if (skb) {
 		skb_reserve(skb, BUF_HEADROOM);
 		skb_put(skb, size);
diff --git a/net/tipc/msg.h b/net/tipc/msg.h
index 5d64596ba987..2c214691037c 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 fb_mtu;
+
 struct tipc_skb_cb {
 	union {
 		struct {
-- 
2.32.0