[Bug 1655225] Re: Under heavy load qemu hits bdrv_error_action: Assertion `error >= 0' failed

ChristianEhrhardt 1655225 at bugs.launchpad.net
Tue Jan 31 15:09:08 UTC 2017


I did some further checks and think the fix is fine.
Yet given the details as Dave outlined above it will be next-to-impossible to verify - that has to be considered when there is time for proposed verification.

I threw some extra upgrade and migration tests at it, but it was fine as
expected.

That said I can't upload it to the queue yet one has to be aware that
the former SRU waits for verification (bugs 1587039 and 1640382).

I pinged seyeongkim who owns the other issues to make him aware.
@chiluk - I highlighted you so you should find it in the IRC log.


Some test references:
- https://bileto.ubuntu.com/excuses/2423/trusty.html
- http://paste.ubuntu.com/23899762/

I didn't run the QA tests from the security Team as I'm currently
debugging an issue in there.

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https://bugs.launchpad.net/bugs/1655225

Title:
  Under heavy load qemu hits bdrv_error_action: Assertion `error >= 0'
  failed

Status in qemu package in Ubuntu:
  New
Status in qemu source package in Trusty:
  New

Bug description:
  [Impact]

   * VM running in QEMU with this message in qemu log
  qemu-system-x86_64: /build/qemu-_D3HGx/qemu-2.0.0+dfsg/block.c:3491: bdrv_error_action: Assertion `error >= 0' failed.

   * This results in the VM needing to be restarted.

  [Test Case]

   * This only reproduces under extremely high I/O load and very infrequently.
     Once per month on major clouds.

  [Regression Potential]

   * Commit 3bbf572345c is included in 2.4.0-rc4 and newer, and has not
  been removed in latest develepment. I have not found any commits
  referencing it as a regressor.

   * Patch adds memory barriers so regressions may show up in the form of
     performance issues.

  [Other Info]

   * Redhat identified this commit as the fix for the issue here
     https://access.redhat.com/solutions/1459913
     https://bugzilla.redhat.com/show_bug.cgi?id=1142857
     https://git.centos.org/blob/rpms!qemu-kvm/05bba06e575829071bce813e12709f9ec477f120/SOURCES!kvm-atomics-add-explicit-compiler-fence-in-__atomic-memo.patch
   * Only apply to Trusty as Xenial and newer have fix already.  Ignoring
     Precise because no currently reported cases.

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