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Re: [libvirt] [PATCH 3/9] lxc: Use atomic ops for driver->nactive



On Wed, Jul 17, 2013 at 03:04:20PM +0200, Michal Privoznik wrote:
> ---
>  src/lxc/lxc_conf.h    |  2 +-
>  src/lxc/lxc_process.c | 10 ++++------
>  2 files changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/src/lxc/lxc_conf.h b/src/lxc/lxc_conf.h
> index 6ca6198..f9a3e53 100644
> --- a/src/lxc/lxc_conf.h
> +++ b/src/lxc/lxc_conf.h
> @@ -77,7 +77,7 @@ struct _virLXCDriver {
>  
>      virSysinfoDefPtr hostsysinfo;
>  
> -    size_t nactive;
> +    unsigned int nactive;
>  
>      virStateInhibitCallback inhibitCallback;
>      void *inhibitOpaque;
> diff --git a/src/lxc/lxc_process.c b/src/lxc/lxc_process.c
> index 1024576..4b83729 100644
> --- a/src/lxc/lxc_process.c
> +++ b/src/lxc/lxc_process.c
> @@ -48,6 +48,7 @@
>  #include "lxc_hostdev.h"
>  #include "virhook.h"
>  #include "virstring.h"
> +#include "viratomic.h"
>  
>  #define VIR_FROM_THIS VIR_FROM_LXC
>  
> @@ -256,8 +257,7 @@ static void virLXCProcessCleanup(virLXCDriverPtr driver,
>      vm->pid = -1;
>      vm->def->id = -1;
>  
> -    driver->nactive--;
> -    if (!driver->nactive && driver->inhibitCallback)
> +    if (virAtomicIntDecAndTest(&driver->nactive) && driver->inhibitCallback)
>          driver->inhibitCallback(false, driver->inhibitOpaque);
>  
>      virLXCDomainReAttachHostDevices(driver, vm->def);
> @@ -1273,9 +1273,8 @@ int virLXCProcessStart(virConnectPtr conn,
>      virDomainObjSetState(vm, VIR_DOMAIN_RUNNING, reason);
>      priv->doneStopEvent = false;
>  
> -    if (!driver->nactive && driver->inhibitCallback)
> +    if (virAtomicIntInc(&driver->nactive) && driver->inhibitCallback)
>          driver->inhibitCallback(true, driver->inhibitOpaque);
> -    driver->nactive++;

I think you need  virAtomicIntInc() == 1 here, otherwise this will
execute on every single VM start, instead of only the first.

>  
>      if (lxcContainerWaitForContinue(handshakefds[0]) < 0) {
>          char out[1024];
> @@ -1458,9 +1457,8 @@ virLXCProcessReconnectDomain(virDomainObjPtr vm,
>          virDomainObjSetState(vm, VIR_DOMAIN_RUNNING,
>                               VIR_DOMAIN_RUNNING_UNKNOWN);
>  
> -        if (!driver->nactive && driver->inhibitCallback)
> +        if (virAtomicIntInc(&driver->nactive) && driver->inhibitCallback)
>              driver->inhibitCallback(true, driver->inhibitOpaque);
> -        driver->nactive++;

Again here, we want == 1.


virAtomicIntInc() == 1, is the pattern the QEMU driver uses for this
code.



Daniel
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