On Sun, 2016-02-21 at 22:17 +0100, Helge Deller wrote:
> On 21.02.2016 22:09, John David Anglin wrote:
> > On 2016-02-21, at 3:28 PM, James Bottomley wrote:
> >
> > > That said, I still can't reproduce this, so you're going to have
> > > to
> > > help me find it. Current theory is ll_merge_request_fn() it
> > > looks like
> > > there's scope for miscalculation in there. Can you instrument
> > > this
> > > line
> > >
> > > /* Merge is OK... */
> > > req->nr_phys_segments = total_phys_segments;
> > >
> > > To add just before the return
> > >
> > > if (req->nr_phys_segments != __blk_recalc_rq_segments(rq->q, rq
> > > ->bio, false)
> > > printk("MISMATCH IN MERGE: got %d, should get %d\n",
> > > req->nr_phys_segments,
> > > __blk_recalc_rq_segments(rq->q, rq->bio, false));
> >
> > This didn't trigger. There were some typos:
>
> It didn't trigger for me either.
OK, can you instrument the same thing in ll_new_hw_segment() after
req->nr_phys_segments += nr_phys_segs;
> > diff --git a/block/blk-merge.c b/block/blk-merge.c
> > index d9c3a75..e8969ef 100644
> > --- a/block/blk-merge.c
> > +++ b/block/blk-merge.c
> > @@ -545,6 +545,12 @@ static int ll_merge_requests_fn(struct
> > request_queue *q, struct request *req,
> >
> > /* Merge is OK... */
> > req->nr_phys_segments = total_phys_segments;
> > +
> > +if (req->nr_phys_segments != __blk_recalc_rq_segments(req->q, req
> > ->bio, false))
> > + printk("MISMATCH IN MERGE: got %d, should get %d\n",
> > + req->nr_phys_segments,
> > + __blk_recalc_rq_segments(req->q, req->bio, false));
> > +
> > return 1;
> > }
>
> Interestingly it now triggered somewhere else...
> I enabled CONFIG_DEBUG_SG, which I had enabled the last few times as
> well, but it now happened
> for the first time:
No, that just means the sg table you initialised was too short: the
last element didn't get a sg_magic set; it's effectively the same
error, just showing differently.
James
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