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

[Mathew Hodson]

** Changed in: qemu (Ubuntu)
   Importance: Undecided => Medium

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

Status in qemu package in Ubuntu:
  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 still exists 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

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