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SubjectRe: 2.4.21-pre3 kernel crash
On Wed, Jan 29 2003, Benjamin Herrenschmidt wrote:
> On Wed, 2003-01-29 at 09:53, Jens Axboe wrote:
> > On Wed, Jan 29 2003, Benjamin Herrenschmidt wrote:
> > > On Tue, 2003-01-28 at 23:06, Jens Axboe wrote:
> > > > On Tue, Jan 28 2003, Larry Sendlosky wrote:
> > > > > I was glad to see the physical page support in 2.4.20.
> > > > > (and also noticed that the current BK tree clobbered it
> > > > > on a patch set from Alan).
> > > > >
> > > > > One question,
> > > > >
> > > > > + lastdataend = bh_phys(bh) + bh->b_size;
> > > > >
> > > > > bh_phys(x) uses bh->b_page. Does it make a difference
> > > > > if bh->b_page is zero? What if someone combines virt and phys
> > > > > buffer addresses in bh list?
> > > >
> > > > Yes good catch! New version attached.
> > >
> > > That's interesting. I wasn't awaye you could have a request
> > > containing such a "mixed" set of bh without valid pages.
> > > Actually, I though b_page was always valid. Looking at
> > > other drivers (typically the the csiss.c driver), it also
> > > unconditionally use b_page & bh_phys(). So either we are
> > > looking at a false problem, or that driver need fixing as
> > > well.
> >
> > b_page is not always valid for IDE, this is a special case. ide-scsi
> > fabricates its own buffer_heads. cciss etc can rely on valid b_page
> > always.
>
> Ok. Well, looking at ide-scsi, I see that:
>
> #if 1
> bh->b_data = sg->address;
> #else
> if (sg->address) {
> bh->b_page = virt_to_page(sg->address);
> bh->b_data = (char *) ((unsigned long) sg->address & ~PAGE_MASK);
> } else if (sg->page) {
> bh->b_page = sg->page;
> bh->b_data = (char *) sg->offset;
> }
> #endif
>
> Can't we just turn that #if 1 into #if 0 ? The case of non segmented
> requests remains, where we have
>
> bh->b_data = pc->scsi_cmd->request_buffer;
> bh->b_size = pc->request_transfer;
>
> But then, can't we use the same approach as above using virt_to_page() ?
>
> I don't say we should do it now. I'm mostly asking for my own eductation
> about all this, though I admit I don't like the "mixing" done in
> ide_build_sglist.

Sure that is a possibility, there's definitely nothing wrong with doing
so.

--
Jens Axboe

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