Re: [Qemu-block] Problem with data miscompare using scsi-hd, cache=none and io=threads

[Daniel Henrique Barboza]

On 05/24/2018 11:04 AM, Stefan Hajnoczi wrote:
> On Tue, May 15, 2018 at 06:25:46PM -0300, Daniel Henrique Barboza wrote:
> > This means that the test executed a write at  LBA 0x94fa and, after
> > confirming that the write was completed, issue 2 reads in the same LBA to
> > assert the written contents and found out a mismatch.
> Have you confirmed this pattern at various levels in the stack:
> 1. Application inside the guest (strace)
> 2. Guest kernel block layer (blktrace)
> 3. QEMU (strace)
> 4. Host kernel block layer (blktrace)

Tested (3). In this case the bug stop reproducing. Not sure if there is
anything related with strace adding a delay back and forth the
preadv/pwritev calls, but the act of attaching strace to the QEMU
process changed the behavior.

Haven't tried the other 3 scenarios. (2) and (4) are definitely worth 
trying it
out, specially (4).

> The key thing is that the write completes before the 2 reads are
> submitted.
>
> Have you tried running the test on bare metal?

Yes. The stress test does not reproduce the miscompare issue when
running on bare metal.


Thanks,

Daniel

> Stefan