[libvirt] [PATCH 08/12] libxl: Use atomic ops for driver->nactive

[Michal Privoznik]

On 30.08.2013 23:46, Jim Fehlig wrote:
> 
> Signed-off-by: Jim Fehlig <jfehlig at suse.com>
> ---
>  src/libxl/libxl_conf.h   |  2 +-
>  src/libxl/libxl_driver.c | 10 ++++------
>  2 files changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/src/libxl/libxl_conf.h b/src/libxl/libxl_conf.h
> index e3875ba..83bb6b9 100644
> --- a/src/libxl/libxl_conf.h
> +++ b/src/libxl/libxl_conf.h
> @@ -90,7 +90,7 @@ struct _libxlDriverPrivate {
>       * then lockless thereafter */
>      libxlDriverConfigPtr config;
>  
> -    size_t nactive;
> +    unsigned int nactive;
>  
>      virStateInhibitCallback inhibitCallback;
>      void *inhibitOpaque;
> diff --git a/src/libxl/libxl_driver.c b/src/libxl/libxl_driver.c
> index e604899..7615cdd 100644
> --- a/src/libxl/libxl_driver.c
> +++ b/src/libxl/libxl_driver.c
> @@ -50,6 +50,7 @@
>  #include "virstring.h"
>  #include "virsysinfo.h"
>  #include "viraccessapicheck.h"
> +#include "viratomic.h"
>  
>  #define VIR_FROM_THIS VIR_FROM_LIBXL
>  
> @@ -265,8 +266,7 @@ libxlVmCleanup(libxlDriverPrivatePtr driver,
>          virDomainObjSetState(vm, VIR_DOMAIN_SHUTOFF, reason);
>      }
>  
> -    driver->nactive--;
> -    if (!driver->nactive && driver->inhibitCallback)
> +    if (virAtomicIntDecAndTest(&driver->nactive) && driver->inhibitCallback)
>          driver->inhibitCallback(false, driver->inhibitOpaque);
>  
>      if ((vm->def->ngraphics == 1) &&
> @@ -655,9 +655,8 @@ libxlVmStart(libxlDriverPrivatePtr driver, virDomainObjPtr vm,
>      if (virDomainSaveStatus(driver->xmlopt, cfg->stateDir, vm) < 0)
>          goto error;
>  
> -    if (!driver->nactive && driver->inhibitCallback)
> +    if (virAtomicIntInc(&driver->nactive) && driver->inhibitCallback)
>          driver->inhibitCallback(true, driver->inhibitOpaque);

Not exactly the same as previous code. Previously, the callback was
called iff nactive == 0; However, with your change the callback is
invoked each time the control gets to the 'if' (as virAtomicIntInc()
returns the *new* value after the increment). I think we want this to be:

if (virAtomicIntInc(&driver->nactive) == 1 && driver->inhibitCallback)

> -    driver->nactive++;
>  
>      event = virDomainEventNewFromObj(vm, VIR_DOMAIN_EVENT_STARTED,
>                                       restore_fd < 0 ?
> @@ -727,9 +726,8 @@ libxlReconnectDomain(virDomainObjPtr vm,
>      vm->def->id = d_info.domid;
>      virDomainObjSetState(vm, VIR_DOMAIN_RUNNING, VIR_DOMAIN_RUNNING_UNKNOWN);
>  
> -    if (!driver->nactive && driver->inhibitCallback)
> +    if (virAtomicIntInc(&driver->nactive) && driver->inhibitCallback)

Same applies here.

>          driver->inhibitCallback(true, driver->inhibitOpaque);
> -    driver->nactive++;
>  
>      /* Recreate domain death et. al. events */
>      libxlCreateDomEvents(vm);
> 

ACK if you fix the issue.

Michal