Messages in this thread | | | Subject | Re: 2.4.21-pre3 kernel crash | From | Benjamin Herrenschmidt <> | Date | 29 Jan 2003 10:44:00 +0100 |
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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.
Ben.
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