This bug is missing log files that will aid in diagnosing the problem.
While running an Ubuntu kernel (not a mainline or third-party kernel)
please enter the following command in a terminal window:
apport-collect 1798110
and then change the status of the bug to 'Confirmed'.
If, due to the nature of the issue you have encountered, you are unable
to run this command, please add a comment stating that fact and change
the bug status to 'Confirmed'.
This change has been made by an automated script, maintained by the
Ubuntu Kernel Team.
** Changed in: linux (Ubuntu)
Status: New => Incomplete
** Tags added: xenial
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https://bugs.launchpad.net/bugs/1798110
Title:
xenial: virtio-scsi: CPU soft lockup due to loop in
virtscsi_target_destroy()
Status in linux package in Ubuntu:
Incomplete
Bug description:
(I'll add the SRU template + testing steps and post to ML shortly.)
A customer reported a CPU soft lockup on Trusty HWE kernel from Xenial
when detaching a virtio-scsi drive, and provided a crashdump that shows
2 things:
1) The soft locked up CPU is waiting for another CPU to finish something,
and that does not happen because the other CPU is infinitely looping in
virtscsi_target_destroy().
2) The loop happens because the 'tgt->reqs' counter is non-zero, and that
probably happened due to a missing decrement in SCSI command requeue path,
exercised when the virtio ring is full.
The reported problem itself happens because of a downstream/SAUCE patch,
coupled with the problem of the missing decrement for the reqs counter.
Introducing a decrement in the SCSI command requeue path resolves the
problem, verified synthetically with QEMU+GDB and with test-case/loop
provided by the customer as problem reproducer.
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