[PATCH 2/2] qemu: Check if driver is still available in qemuStateStop()

[Nikolay Shirokovskiy]

On 12.11.2020 21:45, Michal Privoznik wrote:
> When the host is shutting down then we get PrepareForShutdown
> signal on DBus to which we react by creating a thread which
> runs virStateStop() and thus qemuStateStop(). But if scheduling
> the thread is delayed just a but it may happen that we receive
> SIGTERM (sent by systemd) to which we respond by quitting our
> event loop and cleaning up everything (including drivers). And
> only after that the thread gets to run only to find qemu_driver
> being NULL. At this point there is nothing left to do anyways,
> the event loop is gone so no API call that qemuStateStop() does
> in attempt to save running domains can ever succeed.
> 
> But to be fair, if there was a domain running we would have
> registered shutdown inhibitor so we would not get killed by
> signal. So there is nothing left to do for qemuStateStop()
> anyway.
> 
> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1895359
> 
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
>  src/qemu/qemu_driver.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 05f8eb2cb7..9aa0ce4ec8 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -1046,7 +1046,12 @@ qemuStateStop(void)
>      int state;
>      virDomainPtr *domains = NULL;
>      g_autofree unsigned int *flags = NULL;
> -    g_autoptr(virQEMUDriverConfig) cfg = virQEMUDriverGetConfig(qemu_driver);
> +    g_autoptr(virQEMUDriverConfig) cfg = NULL;
> +
> +    if (!qemu_driver)
> +        return -1;
> +
> +    cfg = virQEMUDriverGetConfig(qemu_driver);
>  
>      if (!(conn = virConnectOpen(cfg->uri)))
>          goto cleanup;
> 

Hi, Michal.

There is a machinery to handle such issues now in libvirt. https://www.redhat.com/archives/libvir-list/2020-November/msg00667.html

Nikolay