[Qemu-devel] [Bug 1813045] [NEW] qemu-ga fsfreeze crashes the kernel

[Qemu-devel] [Bug 1813045] [NEW] qemu-ga fsfreeze crashes the kernel

[Michele Schillaci]

Public bug reported:

We use mainly Cloudlinux, Debian and Centos.
We experienced many crashes on our qemu instances based on Cloudlinux during a snapshot.
The issue is not related to CloudLinux directly, but to Qemu agent, which does not freeze the file system(s) correctly. What is actually happening:

When VM backup is invoked, Qemu agent freezes the file systems, so no single change will be made during the backup. But Qemu agent does not respect the loop* devices in freezing order (we have checked its sources), which leads to the next situation: 
1) freeze loopback fs
              ---> send async reqs to loopback thread
2) freeze main fs
3) loopback thread wakes up and trying to write data to the main fs, which is still frozen, and this finally leads to the hung task and kernel crash. 

I believe this is the culprit:

/dev/loop0 /tmp ext3 rw,nosuid,noexec,relatime,data=ordered 0 0
/dev/loop0 /var/tmp ext3 rw,nosuid,noexec,relatime,data=ordered 0 0

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1813045

Title:
  qemu-ga fsfreeze crashes the kernel

Status in QEMU:
  New

Bug description:
  We use mainly Cloudlinux, Debian and Centos.
  We experienced many crashes on our qemu instances based on Cloudlinux during a snapshot.
  The issue is not related to CloudLinux directly, but to Qemu agent, which does not freeze the file system(s) correctly. What is actually happening:

  When VM backup is invoked, Qemu agent freezes the file systems, so no single change will be made during the backup. But Qemu agent does not respect the loop* devices in freezing order (we have checked its sources), which leads to the next situation: 
  1) freeze loopback fs
                ---> send async reqs to loopback thread
  2) freeze main fs
  3) loopback thread wakes up and trying to write data to the main fs, which is still frozen, and this finally leads to the hung task and kernel crash. 

  I believe this is the culprit:

  /dev/loop0 /tmp ext3 rw,nosuid,noexec,relatime,data=ordered 0 0
  /dev/loop0 /var/tmp ext3 rw,nosuid,noexec,relatime,data=ordered 0 0

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[Bug 1813045] Re: qemu-ga fsfreeze crashes the kernel

[Thomas Huth]

The QEMU project is currently considering to move its bug tracking to another system. For this we need to know which bugs are still valid and which could be closed already. Thus we are setting older bugs to "Incomplete" now.
If you still think this bug report here is valid, then please switch the state back to "New" within the next 60 days, otherwise this report will be marked as "Expired". Or mark it as "Fix Released" if the problem has been solved with a newer version of QEMU already. Thank you and sorry for the inconvenience.

** Changed in: qemu
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1813045

Title:
  qemu-ga fsfreeze crashes the kernel

Status in QEMU:
  Incomplete

Bug description:
  We use mainly Cloudlinux, Debian and Centos.
  We experienced many crashes on our qemu instances based on Cloudlinux during a snapshot.
  The issue is not related to CloudLinux directly, but to Qemu agent, which does not freeze the file system(s) correctly. What is actually happening:

  When VM backup is invoked, Qemu agent freezes the file systems, so no single change will be made during the backup. But Qemu agent does not respect the loop* devices in freezing order (we have checked its sources), which leads to the next situation: 
  1) freeze loopback fs
                ---> send async reqs to loopback thread
  2) freeze main fs
  3) loopback thread wakes up and trying to write data to the main fs, which is still frozen, and this finally leads to the hung task and kernel crash. 

  I believe this is the culprit:

  /dev/loop0 /tmp ext3 rw,nosuid,noexec,relatime,data=ordered 0 0
  /dev/loop0 /var/tmp ext3 rw,nosuid,noexec,relatime,data=ordered 0 0

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[Bug 1813045] Re: qemu-ga fsfreeze crashes the kernel

[Launchpad Bug Tracker]

[Expired for QEMU because there has been no activity for 60 days.]

** Changed in: qemu
       Status: Incomplete => Expired

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https://bugs.launchpad.net/bugs/1813045

Title:
  qemu-ga fsfreeze crashes the kernel

Status in QEMU:
  Expired

Bug description:
  We use mainly Cloudlinux, Debian and Centos.
  We experienced many crashes on our qemu instances based on Cloudlinux during a snapshot.
  The issue is not related to CloudLinux directly, but to Qemu agent, which does not freeze the file system(s) correctly. What is actually happening:

  When VM backup is invoked, Qemu agent freezes the file systems, so no single change will be made during the backup. But Qemu agent does not respect the loop* devices in freezing order (we have checked its sources), which leads to the next situation: 
  1) freeze loopback fs
                ---> send async reqs to loopback thread
  2) freeze main fs
  3) loopback thread wakes up and trying to write data to the main fs, which is still frozen, and this finally leads to the hung task and kernel crash. 

  I believe this is the culprit:

  /dev/loop0 /tmp ext3 rw,nosuid,noexec,relatime,data=ordered 0 0
  /dev/loop0 /var/tmp ext3 rw,nosuid,noexec,relatime,data=ordered 0 0

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[Bug 1813045] Re: qemu-ga fsfreeze crashes the kernel

[Thomas Huth]

See also https://gitlab.com/qemu-project/qemu/-/issues/520

** Bug watch added: gitlab.com/qemu-project/qemu/-/issues #520
   https://gitlab.com/qemu-project/qemu/-/issues/520

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https://bugs.launchpad.net/bugs/1813045

Title:
  qemu-ga fsfreeze crashes the kernel

Status in QEMU:
  Expired

Bug description:
  We use mainly Cloudlinux, Debian and Centos.
  We experienced many crashes on our qemu instances based on Cloudlinux during a snapshot.
  The issue is not related to CloudLinux directly, but to Qemu agent, which does not freeze the file system(s) correctly. What is actually happening:

  When VM backup is invoked, Qemu agent freezes the file systems, so no single change will be made during the backup. But Qemu agent does not respect the loop* devices in freezing order (we have checked its sources), which leads to the next situation: 
  1) freeze loopback fs
                ---> send async reqs to loopback thread
  2) freeze main fs
  3) loopback thread wakes up and trying to write data to the main fs, which is still frozen, and this finally leads to the hung task and kernel crash. 

  I believe this is the culprit:

  /dev/loop0 /tmp ext3 rw,nosuid,noexec,relatime,data=ordered 0 0
  /dev/loop0 /var/tmp ext3 rw,nosuid,noexec,relatime,data=ordered 0 0

To manage notifications about this bug go to:
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