Re: [RFC PATCH] net: Fix one page_pool page leak from skb_frag_unref

[Mina Almasry]

On Wed, May 1, 2024 at 7:24 AM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
>
> On Wed, 1 May 2024 00:48:43 -0700 Mina Almasry wrote:
> > > 1) Revert commit 2cc3aeb5eccc
> > > ("skbuff: Fix a potential race while recycling page_pool packets"). I tested
> > > this btw and it works (for this specific scenario).
> > >
> > > 2) Revert Mina's commit a580ea994fd3 ("net: mirror skb frag ref/unref helpers")
> > > for now.
> >
> > I vote for #1, and IIUC Jakub's feedback, he seems to prefer this as
> > well.
>
> I vote #2, actually :( Or #3 make page pool ref safe to acquire
> concurrently, but that plus fixing all the places where we do crazy
> things may be tricky.
>
> Even taking the ref is not as simple as using atomic_long_inc_not_zero()
> sadly, partly because we try to keep the refcount at one, in an apparent
> attempt to avoid dirtying the cache line twice.
>
> So maybe partial revert to stop be bleeding and retry after more testing
> is the way to go?
>

OK, I will upload a revert sometime today.

> I had a quick look at the code and there is also a bunch of functions
> which "shift" frags from one skb to another, without checking whether
> the pp_recycle state matches.

You posted a diff, I will pick it up in a separate patch.

-- 
Thanks,
Mina