Comment 0 for bug 1826416

A mutual customer is reporting ssh is not working on a Xenial based VM. This VM is running the 4.4 based Xenial kernel and not a custom linux-azure kernel.

After an investigation this is a known old signaling issue. The 4.4 based Xenial kernels require the following patch:

vmbus: fix missing signaling in hv_signal_on_read() (https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=13c5e97701091f9b02ded0c68809f8a6b08c747a).

The patch is not in the upstream stable 4.4 tree, because it’s not needed there.

Compared to the upstream 4.4 tree, Ubuntu 4.4.0-124-generic integrated more hv patches from the mainline kernel, e.g. Drivers: hv: vmbus: finally fix hv_need_to_signal_on_read(), so it must pick up the above patch.

We checked the latest Ubuntu 4.4 kernel (https://kernel.ubuntu.com/git/ubuntu/ubuntu-xenial.git/tree/?h=Ubuntu-4.4.0-146.172) and the patch is also absent there.

The patch (13c5e97701091f9b02ded0c68809f8a6b08c747a) can be cleanly cherry-picked into Ubuntu-4.4.0-146.172.