> On Jun 9, 2016, at 1:37 PM, Benjamin Coddington <bcodding@xxxxxxxxxx> wrote:
>
> On 9 Jun 2016, at 10:17, Weston Andros Adamson wrote:
>
>>> On Jun 8, 2016, at 10:45 AM, Benjamin Coddington <bcodding@xxxxxxxxxx> wrote:
>>>
>>> Hi Dros,
>>>
>>> The client takes this WARN_ON_ONCE path pretty often in
>>> pnfs_generic_pg_test() with SCSI layout type and generic/010:
>>>
>>> 1925 if (pgio->pg_lseg) {
>>> 1926 seg_end = end_offset(pgio->pg_lseg->pls_range.offset,
>>> 1927 pgio->pg_lseg->pls_range.length);
>>> 1928 req_start = req_offset(req);
>>> 1929 WARN_ON_ONCE(req_start >= seg_end);
>>> 1930 /* start of request is past the last byte of this segment */
>>> 1931 if (req_start >= seg_end) {
>>> 1932 /* reference the new lseg */
>>> 1933 if (pgio->pg_ops->pg_cleanup)
>>> 1934 pgio->pg_ops->pg_cleanup(pgio);
>>> 1935 if (pgio->pg_ops->pg_init)
>>> 1936 pgio->pg_ops->pg_init(pgio, req);
>>> 1937 return 0;
>>> 1938 }
>>>
>>> I'm trying to figure out why that's a WARN-able path.. do you recall the
>>> original reason for that warning?
>>
>> What’s happening here is that the pgio descriptor spans multiple layout segments.
>>
>> IIRC this points to a problem with the pg_test call. It shouldn’t allow requests
>> from different lsegs to be coalesced.
>
> Ok, but we're in pg_test right now in something like:
>
> pnfs_generic_pg_test
> bl_pg_test_write
> nfs_pageio_add_request
> nfs_do_writepage
>
> So, bl_pg_test_write is the pg_test op for the block layout, and it calls
> through to pnfs_generic_pg_test to do the job of checking if the request is
> outside the layout.
Hrm, oh this is *in* pnfs_generic_pg_test! Something else is going on here.
It’s been a long time since I was in there, but IIRC the nfs_can_coalesce_requests
call should not be coalescing reqs with different lsegs. It doesn’t appear to check
for that anymore!?
>
> Would you rather keep the warn and have the layout-specific pg_test op check
> that we don't cross a segment boundary? If not, I think we can probably
> drop this warn unless it is useful to the other layouts
I don’t have the cycles right now to dig much further, but this sure looks wrong to me.
Doesn’t the code as-is switch the pgio-wide lseg to the new one from @req, then
return 0, meaning that 0 bytes from @req “fit” into pgio? How is that right?
Doesn’t this use the wrong lseg?
Note that there are currently zero servers (that I am aware of) that hand out
file/flexfile layouts with more than one segment...
-dros
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