SRU request submitted:
https://lists.ubuntu.com/archives/kernel-team/2018-May/092545.html
** Description changed:
+
+ == SRU Justification ==
+ Upstream commit 5b5971df3bc2 introduced a regression in v4.15-rc2. This
+ regression causes a hang on network interface removal in Xen virtual machine.
+
+ This regression is fixed by commit c2d2e6738a209 in v4.16-rc4.
+
+ == Fix ==
+ c2d2e6738a20 ("xen-netfront: Fix hang on device removal")
+
+ == Regression Potential ==
+ Low. Fixes a current regression and specific to Xen.
+
+ == Test Case ==
+ A test kernel was built with this patch and tested by the original bug
reporter.
+ The bug reporter states the test kernel resolved the bug.
+
+
On a hosting platform running Xen hypervisor, in a virtual machine with
Ubuntu 18.04 system and the default kernel from Ubuntu, I try to detach
a virtual network interface. On the Xen side, the virtual interface is
removed from the VM but the kernel still has the interface. Then a
couple of minutes afterwards, the kernel log show this kernel trace:
INFO: task xenwatch:108 blocked for more than 120 seconds.
- Tainted: G W 4.15.0-20-generic #21-Ubuntu
+ Tainted: G W 4.15.0-20-generic #21-Ubuntu
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
xenwatch D 0 108 2 0x80000000
Call Trace:
- __schedule+0x297/0x8b0
- schedule+0x2c/0x80
- xennet_remove+0xda/0x1c0
- ? wait_woken+0x80/0x80
- xenbus_dev_remove+0x54/0xa0
- device_release_driver_internal+0x15b/0x220
- device_release_driver+0x12/0x20
- bus_remove_device+0xec/0x160
- ? xenbus_otherend_changed+0x110/0x110
- device_del+0x13d/0x360
- ? xenbus_otherend_changed+0x110/0x110
- ? xenbus_otherend_changed+0x110/0x110
- device_unregister+0x1a/0x60
- xenbus_dev_changed+0xa3/0x1e0
- ? xenwatch_thread+0xcc/0x160
- frontend_changed+0x21/0x50
- xenwatch_thread+0xc4/0x160
- ? wait_woken+0x80/0x80
- kthread+0x121/0x140
- ? find_watch+0x40/0x40
- ? kthread_create_worker_on_cpu+0x70/0x70
- ret_from_fork+0x35/0x40
+ __schedule+0x297/0x8b0
+ schedule+0x2c/0x80
+ xennet_remove+0xda/0x1c0
+ ? wait_woken+0x80/0x80
+ xenbus_dev_remove+0x54/0xa0
+ device_release_driver_internal+0x15b/0x220
+ device_release_driver+0x12/0x20
+ bus_remove_device+0xec/0x160
+ ? xenbus_otherend_changed+0x110/0x110
+ device_del+0x13d/0x360
+ ? xenbus_otherend_changed+0x110/0x110
+ ? xenbus_otherend_changed+0x110/0x110
+ device_unregister+0x1a/0x60
+ xenbus_dev_changed+0xa3/0x1e0
+ ? xenwatch_thread+0xcc/0x160
+ frontend_changed+0x21/0x50
+ xenwatch_thread+0xc4/0x160
+ ? wait_woken+0x80/0x80
+ kthread+0x121/0x140
+ ? find_watch+0x40/0x40
+ ? kthread_create_worker_on_cpu+0x70/0x70
+ ret_from_fork+0x35/0x40
In the git repository of Linux, the commit
c2d2e6738a209f0f9dffa2dc8e7292fc45360d61 (xen-netfront: Fix hang on
device removal)
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c2d2e6738a209f0f9dffa2dc8e7292fc45360d61
seems to be related to this situation.
I rebuilded the Ubuntu kernel from the package source and applied this
patch. Once the VM has booted with the new kernel, I was able to remove
network interface without hangs from the kernel.
I also booted the VM with the Ubuntu kernel 4.13.0-42-generic and was
able to remove the network interface with success.
ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: linux-image-4.15.0-20-generic 4.15.0-20.21
ProcVersionSignature: Ubuntu 4.15.0-20.21-generic 4.15.17
Uname: Linux 4.15.0-20-generic x86_64
ApportVersion: 2.20.9-0ubuntu7
Architecture: amd64
Date: Wed May 16 16:36:06 2018
ProcEnviron:
- TERM=rxvt-unicode
- PATH=(custom, no user)
- LANG=en_US.UTF-8
- SHELL=/bin/bash
+ TERM=rxvt-unicode
+ PATH=(custom, no user)
+ LANG=en_US.UTF-8
+ SHELL=/bin/bash
SourcePackage: linux-signed
UpgradeStatus: No upgrade log present (probably fresh install)
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https://bugs.launchpad.net/bugs/1771620
Title:
Hang on network interface removal in Xen virtual machine
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