Hello,

On Fri, 6 Dec 2024, David Laight wrote:

The intention of the code seems to be that the minimum table size should be 256 (1 << min). However the code uses max = clamp(20, 5, max_avail) which implies

Actually, it tries to reduce max=20 (max possible) below max_avail: [8 .. max_avail]. Not sure what 5 is here...

the author thought max_avail could be less than 5. But clamp(val, min, max) is only well defined for max >= min. If max < min whether is returns min or max depends on the order of the comparisons.

Looks like max_avail goes below 8 ? What value you see for such small system?

Change to clamp(max_avail, 5, 20) which has the expected behaviour.

It should be clamp(max_avail, 8, 20)

Replace the clamp_val() on the line below with clamp(). clamp_val() is just 'an accident waiting to happen' and not needed here.

OK

Fixes: 4f325e26277b6 (Although I actually doubt the code is used on small memory systems.)

Detected by compile time checks added to clamp(), specifically: minmax.h: use BUILD_BUG_ON_MSG() for the lo < hi test in clamp()

Existing or new check? Does it happen that max_avail is a constant, so that a compile check triggers?

Signed-off-by: David Laight david.laight@aculab.com

The code below looks ok to me but can you change the comments above to more correctly specify the values and if the problem is that max_avail goes below 8 (min).

---

net/netfilter/ipvs/ip_vs_conn.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/ipvs/ip_vs_conn.c b/net/netfilter/ipvs/ip_vs_conn.c index 98d7dbe3d787..c0289f83f96d 100644 --- a/net/netfilter/ipvs/ip_vs_conn.c +++ b/net/netfilter/ipvs/ip_vs_conn.c @@ -1495,8 +1495,8 @@ int __init ip_vs_conn_init(void) max_avail -= 2; /* ~4 in hash row */ max_avail -= 1; /* IPVS up to 1/2 of mem */ max_avail -= order_base_2(sizeof(struct ip_vs_conn));

More likely we can additionally clamp max_avail here:

max_avail = max(min, max_avail);

But your solution solves the problem with less lines.

• max = clamp(max, min, max_avail);
• ip_vs_conn_tab_bits = clamp_val(ip_vs_conn_tab_bits, min, max);

• max = clamp(max_avail, min, max);
• ip_vs_conn_tab_bits = clamp(ip_vs_conn_tab_bits, min, max); ip_vs_conn_tab_size = 1 << ip_vs_conn_tab_bits; ip_vs_conn_tab_mask = ip_vs_conn_tab_size - 1;

2.17.1

Regards

-- Julian Anastasov ja@ssi.bg