The following race is possible when one cpu unregisters the handler while other one is trying to receive a message and call this one:
CPU1: CPU2: inet_diag_rcv() inet_diag_unregister() mutex_lock(&inet_diag_mutex); netlink_rcv_skb(skb, &inet_diag_rcv_msg); if (inet_diag_table[nlh->nlmsg_type] == NULL) /* false handler is still registered */ ... netlink_dump_start(idiagnl, skb, nlh, inet_diag_dump, NULL); cb = kzalloc(sizeof(*cb), GFP_KERNEL); /* sleep here freeing memory * or preempt * or sleep later on nlk->cb_mutex */ spin_lock(&inet_diag_register_lock); inet_diag_table[type] = NULL; ... spin_unlock(&inet_diag_register_lock); synchronize_rcu(); /* CPU1 is sleeping - RCU quiescent * state is passed */ return; /* inet_diag_dump is finally called: */ inet_diag_dump() handler = inet_diag_table[cb->nlh->nlmsg_type]; BUG_ON(handler == NULL); /* OOPS! While we slept the unregister has set * handler to NULL :( */ Grep showed, that the register/unregister functions are called from init/fini module callbacks for tcp_/dccp_diag, so it's OK to use the inet_diag_mutex to synchronize manipulations with the inet_diag_table and the access to it. Signed-off-by: Pavel Emelyanov <[EMAIL PROTECTED]> --- diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c index b017073..5fe32d5 100644 --- a/net/ipv4/inet_diag.c +++ b/net/ipv4/inet_diag.c @@ -853,8 +853,6 @@ static void inet_diag_rcv(struct sk_buff *skb) mutex_unlock(&inet_diag_mutex); } -static DEFINE_SPINLOCK(inet_diag_register_lock); - int inet_diag_register(const struct inet_diag_handler *h) { const __u16 type = h->idiag_type; @@ -863,13 +861,13 @@ int inet_diag_register(const struct inet_diag_handler *h) if (type >= INET_DIAG_GETSOCK_MAX) goto out; - spin_lock(&inet_diag_register_lock); + mutex_lock(&inet_diag_mutex); err = -EEXIST; if (inet_diag_table[type] == NULL) { inet_diag_table[type] = h; err = 0; } - spin_unlock(&inet_diag_register_lock); + mutex_unlock(&inet_diag_mutex); out: return err; } @@ -882,11 +880,9 @@ void inet_diag_unregister(const struct inet_diag_handler *h) if (type >= INET_DIAG_GETSOCK_MAX) return; - spin_lock(&inet_diag_register_lock); + mutex_lock(&inet_diag_mutex); inet_diag_table[type] = NULL; - spin_unlock(&inet_diag_register_lock); - - synchronize_rcu(); + mutex_unlock(&inet_diag_mutex); } EXPORT_SYMBOL_GPL(inet_diag_unregister); - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html