[libvirt] [PATCH] libxl: Fix lock manager lock ordering

[Cole Robinson]

On 10/14/19 5:39 PM, Jim Fehlig wrote:
> The ordering of lock manager locks in the libxl driver has a flaw that was
> uncovered by a migration error path. In the perform phase of migration, the
> source host calls virDomainLockProcessPause to release the lock before
> sending the VM to the destination host. If the send fails an attempt is made
> to reacquire the lock with virDomainLockProcessResume, but that too can fail
> if the destination host has not finished cleaning up the failed VM and
> releasing the lock it acquired when starting to receive the VM.
> 
> This change delays calling virDomainLockProcessResume in libxlDomainStart
> until the VM is successfully created, but before it is unpaused. A similar
> approach is used by the qemu driver, avoiding the need to release the lock
> if VM creation fails. In the migration perform phase, releasing the lock
> with virDomainLockProcessPause is delayed until the VM is successfully
> sent to the destination, which avoids reacquiring the lock if the send
> fails.
> 
> Signed-off-by: Jim Fehlig <jfehlig at suse.com>
> ---
>  src/libxl/libxl_domain.c    | 14 +++++++-------
>  src/libxl/libxl_migration.c | 14 +++++---------
>  2 files changed, 12 insertions(+), 16 deletions(-)

Reviewed-by: Cole Robinson <crobinso at redhat.com>

- Cole