Re: [net-next PATCH v3 4/8] net: Change return type of sk_busy_loop from bool to void
From: Eric Dumazet
Date: Fri Mar 22 2019 - 08:59:20 EST
On Fri, Mar 22, 2019 at 3:33 AM Paolo Abeni <pabeni@xxxxxxxxxx> wrote:
> On Thu, 2019-03-21 at 23:05 -0400, Christoph Paasch wrote:
> > On Thu, Mar 21, 2019 at 12:43 PM Alexander Duyck
> > <alexander.duyck@xxxxxxxxx> wrote:
> > > On Thu, Mar 21, 2019 at 2:45 AM Paolo Abeni <pabeni@xxxxxxxxxx> wrote:
> > > > The following - completely untested - should avoid the unbounded loop,
> > > > but it's not a complete fix, I *think* we should also change
> > > > sk_busy_loop_end() in a similar way, but that is a little more complex
> > > > due to the additional indirections.
> > >
> > > As far as sk_busy_loop_end we could look at just forking sk_busy_loop
> > > and writing a separate implementation for datagram sockets that uses a
> > > different loop_end function. It shouldn't take much to change since
> > > all we would need to do is pass a structure containing the sk and last
> > > pointers instead of just passing the sk directly as the loop_end
> > > argument.
> > >
> > > > Could you please test it?
> > > >
> > > > Any feedback welcome!
> > >
> > > The change below looks good to me.
> > I just tried it out. Worked for me!
> > You can add my Tested-by if you do a formal patch-submission:
> > Tested-by: Christoph Paasch <cpaasch@xxxxxxxxx>
> Thanks for testing!
> I'm trying to reproduce the issue locally, but I'm unable. I think that
> the current UDP implementation is not affected, as we always ensure
> sk_receive_queue is empty before busy polling.
But right after check is done we release the queue lock, so a packet might
come right after the test has been done.
> Unix sockets should not
> be affected, too, as busy polling should not have any effect there
> (sk_napi_id should be never >= MIN_NAPI_ID). Can you reproduce the
> issue on an unpatched, recent, upstream kernel?
> Can you please provide the syzkaller repro?