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

[Robie Basak]

Hello Dave, or anyone else affected,

Accepted qemu into trusty-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/qemu/2.0.0+dfsg-
2ubuntu1.32 in a few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, and change the tag
from verification-needed to verification-done. If it does not fix the
bug for you, please add a comment stating that, and change the tag to
verification-failed.  In either case, details of your testing will help
us make a better decision.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance!

** Changed in: qemu (Ubuntu Trusty)
       Status: New => Fix Committed

** Tags added: verification-needed

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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:
  Fix Released
Status in qemu source package in Trusty:
  Fix Committed

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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