On Thu, Aug 29, 2024 at 03:08:28PM -0700, Jakub Kicinski wrote:

On Thu, 29 Aug 2024 13:11:58 +0000 Joe Damato wrote:

quoted

diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
index 959755be4d7f..ee4f99fd4574 100644
--- a/Documentation/netlink/specs/netdev.yaml
+++ b/Documentation/netlink/specs/netdev.yaml

@@ -244,6 +244,11 @@ attribute-sets:
              threaded mode. If NAPI is not in threaded mode (i.e. uses normal
              softirq context), the attribute will be absent.
         type: u32
+      -
+        name: defer-hard-irqs
+        doc: The number of consecutive empty polls before IRQ deferral ends
+             and hardware IRQs are re-enabled.
+        type: s32

Why is this a signed value? 🤔️

In commit 6f8b12d661d0 ("net: napi: add hard irqs deferral
feature"), napi_defer_hard_irqs was added to struct net_device as an
int. I was trying to match that and thus made the field a signed int
in the napi struct, as well.

It looks like there was a possibility of overflow introduced in that
commit in change_napi_defer_hard_irqs maybe ?

If you'd prefer I could:
  - submit a Fixes to change the net_device field to a u32 and then
    change the netlink code to also be u32
  - add an overflow check (val > U32_MAX) in
    change_napi_defer_hard_irqs

Which would mean for the v2 of this series:
  - drop the overflow check I added in Patch 1
  - Change netlink to use u32 in this patch 

What do you think?

You can use:

	check:
		max: s32-max

to have netlink validate the overflow if you switch to u32.

quoted

   -
     name: queue
     attributes:

quoted

@@ -188,6 +189,10 @@ netdev_nl_napi_fill_one(struct sk_buff *rsp, struct napi_struct *napi,
 			goto nla_put_failure;
 	}
 
+	napi_defer_hard_irqs = napi_get_defer_hard_irqs(napi);

Here, for example the READ_ONCE() wouldn't have been necessary, right?
Cause we are holding rtnl_lock(), just a random thought, not really
actionable.

That's right, yes.

I think it depends on where we land with the wrapper functions? I'll
reply with my thoughts about that in that thread.