After looking again at the code, I think we can
do it in different way:

- IP_VS_DEST_F_AVAILABLE and IP_VS_DEST_F_OVERLOAD are defined
in include/uapi/linux/ip_vs.h but we never export them to user
space. So, we are free to change them. We can move them to 
include/net/ip_vs.h, see below...

- IP_VS_DEST_F_AVAILABLE is changed only under service_mutex,
so we can keep its usage

- IP_VS_DEST_F_OVERLOAD needs different access methods.
We can add 'unsigned long flags2;', may be after l_threshold.
And to switch to such usage (F_OVERLOAD -> FL_OVERLOAD):

	- test_bit(IP_VS_DEST_FL_OVERLOAD, &dest->flags2)
	- set_bit(IP_VS_DEST_FL_OVERLOAD, &dest->flags2)

		Sometimes if (test_bit()) clear_bit() can avoid
		full memory barrier in ip_vs_dest_update_overload()

	- clear_bit(IP_VS_DEST_FL_OVERLOAD, &dest->flags2)
		test_bit() guard can help here too

	As there are other races involved, something like
this can be a starting point for such change. It tries harder
to update the overload flag on dest edit/add but it does not
include the proposed bitops:

diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
index 49297fec448a..b34631270e24 100644