static void unix_peek_fds(struct scm_cookie *scm, struct sk_buff *skb)
{
	scm->fp = scm_fp_dup(UNIXCB(skb).fp);

	/*
	 * Garbage collection of unix sockets starts by selecting a set of
	 * candidate sockets which have reference only from being in flight
	 * (total_refs == inflight_refs).  This condition is checked once during
	 * the candidate collection phase, and candidates are marked as such, so
	 * that non-candidates can later be ignored.  While inflight_refs is
	 * protected by unix_gc_lock, total_refs (file count) is not, hence this
	 * is an instantaneous decision.
	 *
	 * Once a candidate, however, the socket must not be reinstalled into a
	 * file descriptor while the garbage collection is in progress.
	 *
	 * If the above conditions are met, then the directed graph of
	 * candidates (*) does not change while unix_gc_lock is held.
	 *
	 * Any operations that changes the file count through file descriptors
	 * (dup, close, sendmsg) does not change the graph since candidates are
	 * not installed in fds.
	 *
	 * Dequeing a candidate via recvmsg would install it into an fd, but
	 * that takes unix_gc_lock to decrement the inflight count, so it's
	 * serialized with garbage collection.
	 *
	 * MSG_PEEK is special in that it does not change the inflight count,
	 * yet does install the socket into an fd.  The following lock/unlock
	 * pair is to ensure serialization with garbage collection.  It must be
	 * done between incrementing the file count and installing the file into
	 * an fd.
	 *
	 * If garbage collection starts after the barrier provided by the
	 * lock/unlock, then it will see the elevated refcount and not mark this
	 * as a candidate.  If a garbage collection is already in progress
	 * before the file count was incremented, then the lock/unlock pair will
	 * ensure that garbage collection is finished before progressing to
	 * installing the fd.
	 *
	 * (*) A -> B where B is on the queue of A or B is on the queue of C
	 * which is on the queue of listening socket A.
	 */
	spin_lock(&unix_gc_lock);
	spin_unlock(&unix_gc_lock);
}
static void unix_peek_fds(struct scm_cookie *scm, struct sk_buff *skb)
{
	scm->fp = scm_fp_dup(UNIXCB(skb).fp);

	 
	spin_lock(&unix_gc_lock);
	spin_unlock(&unix_gc_lock);
}