Re: [Qemu-block] [Qemu-devel] How to emulate block I/O timeout on qemu side?

[Dongli Zhang]

On 11/13/2018 06:52 AM, Marc Olson via Qemu-devel wrote:
> On 11/11/18 11:36 PM, Dongli Zhang wrote:
>> On 11/12/2018 03:13 PM, Marc Olson via Qemu-devel wrote:
>>> On 11/3/18 10:24 AM, Dongli Zhang wrote:
>>>> The 'write' latency of sector=40960 is set to a very large value. When the 
>>>> I/O
>>>> is stalled in guest due to that sector=40960 is accessed, I do see below
>>>> messages in guest log:
>>>>
>>>> [   80.807755] nvme nvme0: I/O 11 QID 2 timeout, aborting
>>>> [   80.808095] nvme nvme0: Abort status: 0x4001
>>>>
>>>>
>>>> However, then nothing happens further. nvme I/O hangs in guest. I am not
>>>> able to
>>>> kill the qemu process with Ctrl+C. Both vnc and qemu user net do not work. 
>>>> I
>>>> need to kill qemu with "kill -9"
>>>>
>>>>
>>>> The same result for virtio-scsi and qemu is stuck as well.
>>> While I didn't try virtio-scsi, I wasn't able to reproduce this behavior 
>>> using
>>> nvme on Ubuntu 18.04 (4.15). What image and kernel version are you trying
>>> against?
>> Would you like to reproduce the "aborting" message or the qemu hang?
> I could not reproduce IO hanging in the guest, but I can reproduce qemu 
> hanging.
>> guest image: ubuntu 16.04
>> guest kernel: mainline linux kernel (and default kernel in ubuntu 16.04)
>> qemu: qemu-3.0.0 (with the blkdebug delay patch)
>>
>> Would you be able to see the nvme abort (which is indeed not supported by 
>> qemu)
>> message in guest kernel?
> Yes.
>> Once I see that message, I would not be able to kill the qemu-system-x86_64
>> command line with Ctrl+C.
> 
> I missed this part. I wasn't expecting to handle very long timeouts, but what
> appears to be happening is that the sleep doesn't get interrupted on 
> shutdown. I
> suspect something like this, on top of the series I sent last night, should 
> help:
> 
> diff --git a/block/blkdebug.c b/block/blkdebug.c
> index 6b1f2d6..0bfb91b 100644
> --- a/block/blkdebug.c
> +++ b/block/blkdebug.c
> @@ -557,8 +557,11 @@ static int rule_check(BlockDriverState *bs, uint64_t
> offset, uint64_t bytes)
>              remove_active_rule(s, delay_rule);
>          }
> 
> -        if (latency != 0) {
> -            qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, latency);
> +        while (latency > 0 && 
> !aio_external_disabled(bdrv_get_aio_context(bs))) {
> +            int64_t cur_latency = MIN(latency, 1000000000ULL);
> +
> +            qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, cur_latency);
> +            latency -= cur_latency;
>          }
>      }
> 
> 
> /marc
> 
> 

I am able to interrupt qemu with above patch to periodically wake up and sleep
again.

Dongli Zhang