Messages in this thread Patch in this message | | | Date | Wed, 17 Oct 2007 21:49:44 +0200 | From | Jens Axboe <> | Subject | Re: [bug] ata subsystem related crash with latest -git |
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On Wed, Oct 17 2007, Jens Axboe wrote: > On Wed, Oct 17 2007, Linus Torvalds wrote: > > > > > > On Wed, 17 Oct 2007, Ingo Molnar wrote: > > > > > > nope, this did not help. First bootup went fine, second bootup crashed > > > again (see below), without hitting the BUG_ON(). > > > > I think you'll always hit it if you have a scatter-gather list that is > > exactly filled up. > > > > Why? Because those things do "sg_next()" on the last entry, and as > > mentioned, that ends up actually accessing one past the end - even if the > > end result is not actually ever *used* (because we just effectively > > incremented it to past the last entry when the code was done with the SG > > list).
Well, hang on - where does it end up doing sg_next() on the LAST sg entry? I'd argue that this is a bug, like it was in ll_rw_blk.c. I still agree that I should make the interface more robust, I just don't see where libata ends up doing the sg_next() on the last entry.
I'm assuming that Ingo is using the previous patches, so that blk_rq_map_sg() is using this construct:
new_segment: if (!sg) sg = sglist; else sg = sg_next(sg);
and the memset() in scsi_alloc_sgtable(), which I'm pretty sure he is. I'm assuming we're not hitting pio paths, so there are no manual sg_next() calls. Ingo, if you care, can you test this one as well?
No rush, as mentioned I'll be back tomorrow morning...
diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c index bbaa545..0246b61 100644 --- a/drivers/ata/libata-core.c +++ b/drivers/ata/libata-core.c @@ -4664,7 +4664,7 @@ static int ata_sg_setup(struct ata_queued_cmd *qc) { struct ata_port *ap = qc->ap; struct scatterlist *sg = qc->__sg; - struct scatterlist *lsg = sg_last(qc->__sg, qc->n_elem); + struct scatterlist *lsg = &qc->__sg[qc->n_elem - 1]; int n_elem, pre_n_elem, dir, trim_sg = 0; VPRINTK("ENTER, ata%u\n", ap->print_id); -- Jens Axboe
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