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    Subject[PATCH 5.13 598/800] net: tipc: fix FB_MTU eat two pages
    Date
    From: Menglong Dong <dong.menglong@zte.com.cn>

    [ Upstream commit 0c6de0c943dbb42831bf7502eb5c007f71e752d2 ]

    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>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 {
    --
    2.30.2


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