netdev - Re: [PATCH net v1] netmem: fix skb_frag_address

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Message-ID: <CAHS8izOMfmj6R8OReNqvoasb_b0M=gsnrCOv3budBRXrYjO67g@mail.gmail.com>
Date: Tue, 17 Jun 2025 14:52:17 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Stanislav Fomichev <stfomichev@...il.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	ap420073@...il.com
Subject: Re: [PATCH net v1] netmem: fix skb_frag_address_safe with unreadable skbs

On Tue, Jun 17, 2025 at 2:30 PM Stanislav Fomichev <stfomichev@...il.com> wrote:
>
> On 06/17, Mina Almasry wrote:
> > On Tue, Jun 17, 2025 at 2:09 PM Mina Almasry <almasrymina@...gle.com> wrote:
> > >
> > > skb_frag_address_safe() needs a check that the
> > > skb_frag_page exists check similar to skb_frag_address().
> > >
> > > Cc: ap420073@...il.com
> > >
> >
> > Sorry, I realized right after hitting send, I'm missing:
> >
> > Fixes: 9f6b619edf2e ("net: support non paged skb frags")
> >
> > I can respin after the 24hr cooldown.
>
> The function is used in five drivers, none of which support devmem tx,
> does not look like there is a reason to route it via net.
>
> The change it self looks good, but not really sure it's needed.
> skb_frag_address_safe is used in some pass-data-via-descriptor-ring mode,
> I don't see 'modern' drivers (besides bnxt which added this support in 2015)
> use it.

Meh, a judgement call could be made here.  I've generally tried to
make sure skb helpers are (unreadable) netmem compatible without a
thorough analysis of all the callers to make sure they do or will one
day use (unreadable) netmem. Seems better to me to fix this before
some code path that plumbs unreadable memory to the helper is actually
merged and that code starts crashing.

Similarly I put this in net because it's a fix and not a feature. I
can send to net-next if preferred.