Re: [PATCH v3] RDMA/core: Fix race when resolving IP address

[Jason Gunthorpe]

On Mon, Jul 08, 2019 at 07:22:45PM +0000, Mark Bloch wrote:
> 
> 
> On 7/8/19 11:47 AM, Dag Moxnes wrote:
> > Thanks Jason,
> > 
> > Regards,
> > Dag
> > 
> > Den 08.07.2019 19:50, skrev Jason Gunthorpe:
> >> On Mon, Jul 08, 2019 at 01:16:24PM +0200, Dag Moxnes wrote:
> >>> Use neighbour lock when copying MAC address from neighbour data struct
> >>> in dst_fetch_ha.
> >>>
> >>> When not using the lock, it is possible for the function to race with
> >>> neigh_update, causing it to copy an invalid MAC address.
> >>>
> >>> It is possible to provoke this error by calling rdma_resolve_addr in a
> >>> tight loop, while deleting the corresponding ARP entry in another tight
> >>> loop.
> >>>
> >>> This will cause the race shown it the following sample trace:
> >>>
> >>> rdma_resolve_addr()
> >>> ÂÂ rdma_resolve_ip()
> >>> ÂÂÂÂ addr_resolve()
> >>> ÂÂÂÂÂÂ addr_resolve_neigh()
> >>> ÂÂÂÂÂÂÂÂ fetch_ha()
> >>> ÂÂÂÂÂÂÂÂÂÂ dst_fetch_ha()
> >>> ÂÂÂÂÂÂÂÂÂÂÂÂ n->nud_state == NUD_VALID
> >> It isn't nud_state that is the problem here, it is the parallel
> >> memcpy's onto ha. I fixed the commit message
> >>
> >> This could also have been solved by using the ha_lock, but I don't
> >> think we have a reason to particularly over-optimize this.
> 
> Sorry I'm late to the party, but why not just use: neigh_ha_snapshot()?

Yes, that is much better, please respin this

Thanks,
Jason