Re: A new ide warning message

[Bartlomiej Zolnierkiewicz]

On Fri, 2 Aug 2002, Jens Axboe wrote:

> On Fri, Aug 02 2002, Jens Axboe wrote:
> > On Fri, Aug 02 2002, Marcin Dalecki wrote:
> > > U?ytkownik Stephen Lord napisa?:
> > > >In 2.5.30 I started getting these warning messages out ide during
> > > >the mount of an XFS filesystem:
> > > >
> > > >ide-dma: received 1 phys segments, build 2
> > > >
> > > >Can anyone translate that into English please.
> > >
> > > It can be found in pcidma.c.
> > > It is repoting that we have one physical segment needed by
> > > the request in question but the sctter gather list allocation
> > > needed to break it up for mapping in two.
> >
> > You don't seem to realise that this is a BUG (somewhere, could even be
> > in the generic mapping functions)! blk_rq_map_sg() must never map a
> > request to more entries that rq->nr_segments, that's just very wrong.
> >
> > That's why I'm suspecting the recent pcidma changes. Just a feeling, I
> > have not looked at them.
>
> I'll take that back. Having looked at Adam's changes there are perfectly
> fine. I'm now putting my money on IDE breakage somewhere instead. It

Look again Jens. Adam's changes made IDE queue handling inconsistent.
hint: 2 * 127 != 255

But noticed warning deals with design of ll_rw_blk.c. ;-)
(right now max_segment_size have to be max bv->bv_len aligned)

Jens, please look at segment checking/counting code, it does it on
bv->bv_len (4kb most likely) not sector granuality...

So for not 4kb aligned max_segment_size we will get new segment...

Best fix will be to make block layer count sectors not bv->bv_len...

btw. I like Adam's patch but it was draft not to include in mainline (?).
--
Bartlomiej

> would be interesting to dump request state when this happens. Stephen,
> can you reproduce this at will?
>
> --
> Jens Axboe