*** This bug is a duplicate of bug 1840076 ***
https://bugs.launchpad.net/bugs/1840076
Thanks for the bug report, this has been applied to the master-next branch of:
* Disco -
https://kernel.ubuntu.com/git/ubuntu/ubuntu-disco.git/commit/?h=master-next&id=e156b3ed11e418de90b15389a6af7187ace0184b
It's scheduled to be released on the next SRU cycle,
And the master branch of:
* Bionic -
https://kernel.ubuntu.com/git/ubuntu/ubuntu-bionic.git/commit/?h=master-next&id=683f56d305988dda311e928fba080edb758c8d13
* Eoan -
https://kernel.ubuntu.com/git/ubuntu/ubuntu-eoan.git/commit/?h=master-next&id=d10e0cc113c9e1b64b5c6e3db37b5c839794f3df
Therefor I will mark this as a duplicate of bug 1840076 to keep track of
the release status.
** This bug has been marked a duplicate of bug 1840076
Disco update: upstream stable patchset 2019-08-13
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https://bugs.launchpad.net/bugs/1844421
Title:
Linux VM deadlock during migration
Status in linux package in Ubuntu:
Confirmed
Bug description:
The following program will cause a Linux VM running under Xen to
deadlock if a suspend/migrate is attempted:
-----
import pyxs.client
import time
c = pyxs.client.Client(xen_bus_path="/dev/xen/xenbus")
c.connect()
c.transaction()
while True:
time.sleep(1000)
-----
When control/shutdown == "suspend", the kernel calls do_suspend()
which does a number of steps including freezing processes. It then
calls xs_suspend() to suspend xenstore, which takes some locks and
waits for all transactions to complete so that no new activity can
start while the VM is suspending:
-----
xs_suspend():
mutex_lock(&xs_state.transaction_mutex);
wait_event(xs_state.transaction_wq,
atomic_read(&xs_state.transaction_count) == 0); <-- the
xenwatch thread is waiting here
down_write(&xs_state.watch_mutex);
mutex_lock(&xs_state.request_mutex);
mutex_lock(&xs_state.response_mutex);
-----
The xenwatch thread is waiting for all outstanding transactions to
complete. However, by this point the processes have been frozen so any
outstanding transactions won't complete.
This affects all versions of Linux back to at least v3.2, but has been
fixed in v5.2-rc3 (see
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=867cefb4cb1012f42cada1c7d1f35ac8dd276071)
A backport to released Ubuntu kernels is requested.
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