Some functions in the datapath code are factored out so that each
one has a stack frame smaller than 1024 bytes with gcc. However,
when compiling with clang, the functions are inlined more aggressively
and combined again so we get

net/openvswitch/datapath.c:1124:12: error: stack frame size of 1528 bytes in function 'ovs_flow_cmd_set' [-Werror,-Wframe-larger-than=]

Marking both get_flow_actions() and ovs_nla_init_match_and_action()
as 'noinline_for_stack' gives us the same behavior that we see with
gcc, and no warning. Note that this does not mean we actually use
less stack, as the functions call each other, and we still get
three copies of the large 'struct sw_flow_key' type on the stack.

The comment tells us that this was previously considered safe,
presumably since the netlink parsing functions are called with
a known backchain that does not also use a lot of stack space.

Fixes: 9cc9a5cb ("datapath: Avoid using stack larger than 1024.")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>