Re: MPSAFE and KERNEL_LOCK

[Michael van Elst <mlelstv%serpens.de@localhost>]

On Mon, May 14, 2018 at 12:00:44PM +0900, Ryota Ozaki wrote:
> On Fri, May 11, 2018 at 6:41 PM Ryota Ozaki <ozaki-r%netbsd.org@localhost> wrote:
> 
> 
> > On Fri, May 11, 2018 at 3:53 PM Michael van Elst <mlelstv%serpens.de@localhost>
> wrote:
> 
> > > A traditional ethernet driver receives input via an interrupt routine
> > > and passes packets to ether_input(). The data is protected by disabling
> > > the receive interrupt.
> 
> > > In multiprocessor land, the same is achieved by also acquiring the
> > > big kernel lock.
> 
> > > Current code however queues incoming packets in a percpuq and passes
> > > things through a softint tagged as MPSAFE. The softint handler is
> calling
> > > ether_input without holding the kernel lock.
> 
> > > There is another unprotected path in bpf_write calling into the
> > > _if_input vector directly without locking (bpf device is tagged MPSAFE)
> > > and without disabling interrupts.
> 
> > > Did I miss something?
> 
> > You're right.
> 
> > Not holding KERNEL_LOCK in ether_input can be problematic if we use
> > CARP and/or AGR (and NETATALK) that are not MP-safe. Also calling
> > _if_ipnput without splsoftnet from bpf_write is problematic as you said.
> 
> > The following patch should fix the issue:
> >     http://www.netbsd.org/~ozaki-r/fix-if_input.diff
> 
> I committed the patch with the same fix for ether_input from bridge_output.


This will need a pullup to netbsd-8 too.


-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."