Re: kern/42662: iop driver makes kernel crash or freeze

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Mon, Feb 08, 2010 at 08:21:09PM +0300, Aleksej Saushev wrote:
> Manuel Bouyer <bouyer%antioche.eu.org@localhost> writes:
> 
> > On Sat, Jan 30, 2010 at 06:42:37PM +0300, Aleksej Saushev wrote:
> >> I applied it to the current instead, it crashes with the same diagnostic
> >> message and similar backtrace, only it seems to do it a bit later.
> >> I can try to replace as many instances of the pattern as needed,
> >> can you recommend how many of them? All in that subroutine?
> >
> > All of them, mixing PRE and POST in bus_dma(9) is not allowed.
> > I also found one mistake where a PRE should have been a POST.
> > Please try the attached patch (still against netbsd-5).
> 
> The following fixes the problem for me, I can boot installation CD and
> have access to disk storage (am able to read disklabel).
> 
> --- sys/dev/i2o/iop.c 21 Oct 2009 21:12:05 -0000      1.77
> +++ sys/dev/i2o/iop.c 8 Feb 2010 17:19:57 -0000
> @@ -928,7 +928,7 @@
>           BUS_DMASYNC_PREWRITE);
>       memset(st, 0, sizeof(*st));
>       bus_dmamap_sync(sc->sc_dmat, sc->sc_scr_dmamap, 0, sizeof(*st),
> -         BUS_DMASYNC_PREREAD|BUS_DMASYNC_POSTWRITE);
> +         BUS_DMASYNC_POSTWRITE);
>  
>       if ((rv = iop_post(sc, (u_int32_t *)&mf)) != 0)
>               return (rv);
> @@ -993,7 +993,7 @@
>           BUS_DMASYNC_PREWRITE);
>       *sw = 0;
>       bus_dmamap_sync(sc->sc_dmat, sc->sc_scr_dmamap, 0, sizeof(*sw),
> -         BUS_DMASYNC_PREREAD|BUS_DMASYNC_POSTWRITE);
> +         BUS_DMASYNC_POSTWRITE);
>  
>       if ((rv = iop_post(sc, mb)) != 0)
>               return (rv);

But the third bus_dmamap_sync() fix is probably also required, the
bus_dmamap_sync usage here is wrong and things will go wrong on any
platform where a bus_dmamap_sync() is more than a simple memory
barrier. On i386 you won't see it; you may on amd64 with
more than 4Gb ram (depending on how the memory used here was allocated).

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--