netdev - Re: [PATCH net-next 2/5] netdev-genl: Dump napi_defer_hard

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Message-ID: <ZtIsHQoAEk1wfq0P@LQ3V64L9R2>
Date: Fri, 30 Aug 2024 21:31:25 +0100
From: Joe Damato <jdamato@...tly.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: netdev@...r.kernel.org, edumazet@...gle.com, amritha.nambiar@...el.com,
	sridhar.samudrala@...el.com, sdf@...ichev.me, bjorn@...osinc.com,
	hch@...radead.org, willy@...radead.org,
	willemdebruijn.kernel@...il.com, skhawaja@...gle.com,
	Martin Karsten <mkarsten@...terloo.ca>,
	Donald Hunter <donald.hunter@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Paolo Abeni <pabeni@...hat.com>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Daniel Jurgens <danielj@...dia.com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 2/5] netdev-genl: Dump napi_defer_hard_irqs

On Fri, Aug 30, 2024 at 01:28:08PM -0700, Jakub Kicinski wrote:
> On Fri, 30 Aug 2024 10:10:47 +0100 Joe Damato wrote:
> > > > +        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's probably because int is the default type in C.
> The choice of types in netlink feels more deliberate.
> 
> > 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?
> 
> Whether we want to clean things up internally is up to you, the overflow
> check you're adding in sysfs seems good. We can use u32 in netlink, with
> a check: max: s32-max and lift this requirement later if we ever need
> the 32nd bit?

OK, u32 + check for max: s32-max seems good.

Is the overflow check in sysfs a fixes I send separately or can I
sneak that into this series?