4.5-rc iser issues

[Sagi Grimberg]

> Hi Sagi,

Hey,

>> But I don't think simply not cloning the biovecs is the right thing
>> to do in the end.  This must be something with the bvec iterators.
>
> I agree with Christoph, and there might be issues somewhere.
>

Me too, it was just an isolation step...

>>  From the log:
>> iser: sg[0] dma_addr:0x85FC06000 off:0x0 sz:0x200 dma_len:0x200
>> iser: sg[1] dma_addr:0x860334000 off:0x0 sz:0x200 dma_len:0x200 <-- gap
>> iser: sg[2] dma_addr:0x860335000 off:0x0 sz:0x200 dma_len:0x200 <-- gap
>
> The above gap shouldn't have come since blk_bio_segment_split() splits
> out one new bio if gap is detected.
>
> Sort of the following code can be added in driver or prep_fn to check if
> bvec of  the rq is correct:
>
> rq_for_each_segment(bvec, sc->request, iter) {
>       //check if there is gap between bvec
> }

I added this indication and the gap detection does trigger a bio
split.

>
> I don't know how to use iser, and looks everything works fine after
> I setup virt boundary as 4095 for null_blk by the attachment
> patch.

That's probably because it's artificial and there is no HW with a real
limitation...

>
>> Full quote for Ming:
>>
>> On Sun, Feb 14, 2016 at 04:02:18PM +0200, Sagi Grimberg wrote:
>>>
>>>>> I'm bisecting now, there are a couple of patches from Ming in
>>>>> the area of the bio splitting code...
>>>>>
>>>>> CC'ing Ming, Linux-block and Linux-nvme as iser is identical to nvme
>>>>> wrt the virtual boundary so I think nvme will break as well.
>
> The bisected commit is merged to v4.3, and looks no such kind of
> report from nvme.

I'm wandering how can that be... because clearly iser is seeing gaps
which like nvme, it can't handle those. Maybe this is scsi specific?