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    Subject[2/3] [NEIGH] Fix add_timer race in neigh_add_timer
    [NEIGH] Fix add_timer race in neigh_add_timer

    neigh_add_timer cannot use add_timer unconditionally. The reason is that
    by the time it has obtained the write lock someone else (e.g., neigh_update)
    could have already added a new timer.

    So it should only use mod_timer and deal with its return value accordingly.

    This bug would have led to rare neighbour cache entry leaks.

    Signed-off-by: Herbert Xu <>
    Visit Openswan at
    Email: Herbert Xu ~{PmV>HI~} <>
    Home Page:
    PGP Key:
    diff --git a/net/core/neighbour.c b/net/core/neighbour.c
    --- a/net/core/neighbour.c
    +++ b/net/core/neighbour.c
    @@ -816,10 +816,10 @@ static void neigh_timer_handler(unsigned

    if (neigh->nud_state & NUD_IN_TIMER) {
    - neigh_hold(neigh);
    if (time_before(next, jiffies + HZ/2))
    next = jiffies + HZ/2;
    - neigh_add_timer(neigh, next);
    + if (!mod_timer(&neigh->timer, next))
    + neigh_hold(neigh);
    if (neigh->nud_state & (NUD_INCOMPLETE | NUD_PROBE)) {
    struct sk_buff *skb = skb_peek(&neigh->arp_queue);
     \ /
      Last update: 2005-10-23 09:34    [W:0.020 / U:3.208 seconds]
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