On Tue, Nov 02, 2021 at 02:22:15AM +0000, Shinichiro Kawasaki wrote:
> On Nov 01, 2021 / 17:01, Jens Axboe wrote:
> > On 11/1/21 6:41 AM, Jens Axboe wrote:
> > > On 11/1/21 2:34 AM, Shinichiro Kawasaki wrote:
> > >> I tried the latest linux-block/for-next branch tip (git hash b43fadb6631f and
> > >> observed a process hang during blktests block/005 run on a NVMe device.
> > >> Kernel message reported "INFO: task check:1224 blocked for more than 122
> > >> seconds." with call trace [1]. So far, the hang is 100% reproducible with my
> > >> system. This hang is not observed with HDDs or null_blk devices.
> > >>
> > >> I bisected and found the commit 4f5022453acd ("nvme: wire up completion batching
> > >> for the IRQ path") triggers the hang. When I revert this commit from the
> > >> for-next branch tip, the hang disappears. The block/005 test case does IO
> > >> scheduler switch during IO, and the completion path change by the commit looks
> > >> affecting the scheduler switch. Comments for solution will be appreciated.
> > >
> > > I'll take a look at this.
> >
> > I've tried running various things most of the day, and I cannot
> > reproduce this issue nor do I see what it could be. Even if requests are
> > split between batched completion and one-by-one completion, it works
> > just fine for me. No special care needs to be taken for put_many() on
> > the queue reference, as the wake_up() happens for the ref going to zero.
> >
> > Tell me more about your setup. What does the runtimes of the test look
> > like? Do you have all schedulers enabled? What kind of NVMe device is
> > this?
>
> Thank you for spending your precious time. With the kernel without the hang,
> the test case completes around 20 seconds. When the hang happens, the check
> script process stops at blk_mq_freeze_queue_wait() at scheduler change, and fio
> workload processes stop at __blkdev_direct_IO_simple(). The test case does not
> end, so I need to reboot the system for the next trial. While waiting the test
> case completion, the kernel repeats the same INFO message every 2 minutes.
>
> Regarding the scheduler, I compiled the kernel with mq-deadline and kyber.
>
> The NVMe device I use is a U.2 NVMe ZNS SSD. It has a zoned name space and
> a regular name space, and the hang is observed with both name spaces. I have
> not yet tried other NVME devices, so I will try them.
>
> >
> > FWIW, this is upstream now, so testing with Linus -git would be
> > preferable.
>
> I see. I have switched from linux-block for-next branch to the upstream branch
> of Linus. At git hash 879dbe9ffebc, and still the hang is observed.
Can you post the blk-mq debugfs log after the hang is triggered?
(cd /sys/kernel/debug/block/nvme0n1 && find . -type f -exec grep -aH . {} \;)
Thanks
Ming
