Re: WARNING: CPU: 2 PID: 207 at drivers/nvme/host/core.c:527 nvme_setup_cmd+0x3d3

Jens Axboe
2018-01-30T20:32:25Z

On 1/30/18 1:30 PM, Keith Busch wrote:
> On Tue, Jan 30, 2018 at 08:57:49AM -0700, Jens Axboe wrote:
>>
>> Looking at the disassembly, 'n' is 2 and 'segments' is 0xffff.
>
> Is this still a problem if you don't use an IO scheduler? With deadline,
> I'm not finding any path to bio_attempt_discard_merge which is where the
> nr_phys_segments is supposed to get it set to 2. Not sure how it could
> becmoe 0xffff, though.

blk_mq_make_request() -> blk_mq_sched_bio_merge() -> __blk_mq_sched_bio_merge()
-> blk_mq_attempt_merge() -> bio_attempt_discard_merge()

Doesn't matter what IO scheduler you use.

I don't know if it triggers without a scheduler. I've been running this code
continually on the laptop (always do), and haven't seen it before today.

--
Jens Axboe