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[Qemu-devel] [Bug 1681439] Re: qemu-system-x86_64: hw/ide/core.c:685: id

From: Michał Kępień
Subject: [Qemu-devel] [Bug 1681439] Re: qemu-system-x86_64: hw/ide/core.c:685: ide_cancel_dma_sync: Assertion `s->bus->dma->aiocb == NULL' failed.
Date: Wed, 12 Apr 2017 07:51:55 -0000

> > ide_cancel_dma_sync() is also invoked from bmdma_cmd_writeb() and this
> > is in fact the code path taken when the assertion fails.
> > 
> Yep, I wonder why your guest is trying to cancel DMA, though? Something
> else is probably going wrong first.

Beats me.

> Can you compile QEMU from a branch and let me know what kind of info it
> barfs out when it dies?
> https://github.com/jnsnow/qemu/commit/2baa57a58bba00a45151d8544cfd457197ecfa39
> Please make backups of your data as appropriate as this is a development
> branch not suitable for production use (etc etc etc!)
> It's just some dumb printfs so I can see what the device was up to when
> it decided to reset itself. I'm hoping that if I can see what command it
> is trying to cancel I can work out why it isn't getting canceled correctly.

It looks like the command being canceled when the assertion fails is
DSM, which explains why it does not happen with TRIM disabled (I retried
the test twice to make sure the canceled command is consistent; it is):

    $ tail -20 qemu.log
    == ide_cancel_dma_sync ==
    ATA Registers:
    cmd 0x06
    feature     0x01
    error       0x00
    nsector     0x00000001
    sector      0x00
    lcyl        0x00
    hcyl        0x00
    hob_feature 0x00
    hob_nsector 0x00
    hob_sector  0x00
    hob_lcyl    0x00
    hob_hcyl    0x00
    select      0x60
    status      0x58
    lba48       0x00000000
    qemu-system-x86_64: hw/ide/core.c:704: ide_cancel_dma_sync: Assertion 
`s->bus->dma->aiocb == NULL' failed.
    $ grep ^cmd qemu.log | sort | uniq -c
        128 cmd 0x06
     151854 cmd 0xc8
     217496 cmd 0xca

I am happy to help if any further debugging is required.

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  qemu-system-x86_64: hw/ide/core.c:685: ide_cancel_dma_sync: Assertion
  `s->bus->dma->aiocb == NULL' failed.

Status in QEMU:

Bug description:
  Since upgrading to QEMU 2.8.0, my Windows 7 64-bit virtual machines
  started crashing due to the assertion quoted in the summary failing.
  The assertion in question was added by commit 9972354856 ("block: add
  BDS field to count in-flight requests").  My tests show that setting
  discard=unmap is needed to reproduce the issue.  Speaking of
  reproduction, it is a bit flaky, because I have been unable to come up
  with specific instructions that would allow the issue to be triggered
  outside of my environment, but I do have a semi-sane way of testing that
  appears to depend on a specific initial state of data on the underlying
  storage volume, actions taken within the VM and waiting for about 20

  Here is the shortest QEMU command line that I managed to reproduce the
  bug with:

      qemu-system-x86_64 \
          -machine pc-i440fx-2.7,accel=kvm \
          -m 3072 \
          -drive file=/dev/lvm/qemu,format=raw,if=ide,discard=unmap \
        -netdev tap,id=hostnet0,ifname=tap0,script=no,downscript=no,vhost=on \
          -device virtio-net-pci,netdev=hostnet0 \
        -vnc :0

  The underlying storage (/dev/lvm/qemu) is a thin LVM snapshot.

  QEMU was compiled using:

      ./configure --python=/usr/bin/python2.7 --target-list=x86_64-softmmu
      make -j3

  My virtualization environment is not really a critical one and
  reproduction is not that much of a hassle, so if you need me to gather
  further diagnostic information or test patches, I will be happy to help.

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