RE: [PATCH v4 5/6] net/colo-compare.c, softmmu/vl.c: Check that colo-compare is active

["Zhang, Chen" <chen.zhang@intel.com>]

> -----Original Message-----
> From: Lukas Straub <lukasstraub2@web.de>
> Sent: Monday, May 4, 2020 6:28 PM
> To: qemu-devel <qemu-devel@nongnu.org>
> Cc: Zhang, Chen <chen.zhang@intel.com>; Li Zhijian
> <lizhijian@cn.fujitsu.com>; Jason Wang <jasowang@redhat.com>; Marc-
> André Lureau <marcandre.lureau@redhat.com>; Paolo Bonzini
> <pbonzini@redhat.com>
> Subject: [PATCH v4 5/6] net/colo-compare.c, softmmu/vl.c: Check that colo-
> compare is active
> 
> If the colo-compare object is removed before failover and a checkpoint
> happens, qemu crashes because it tries to lock the destroyed event_mtx in
> colo_notify_compares_event.
> 
> Fix this by checking if everything is initialized by introducing a new variable
> colo_compare_active which is protected by a new mutex
> colo_compare_mutex. The new mutex also protects against concurrent
> access of the net_compares list and makes sure that
> colo_notify_compares_event isn't active while we destroy event_mtx and
> event_complete_cond.
> 
> With this it also is again possible to use colo without colo-compare (periodic
> mode) and to use multiple colo-compare for multiple network interfaces.
> 

Hi Lukas,

For this case I think we don't need to touch vl.c code, we can solve this issue from another perspective:
How to remove colo-compare?
User will use qemu-monitor or QMP command to disable an object, so we just need return operation failed
When user try to remove colo-compare object while COLO is running.

Thanks
Zhang Chen

> Signed-off-by: Lukas Straub <lukasstraub2@web.de>
> ---
>  net/colo-compare.c | 35 +++++++++++++++++++++++++++++------
>  net/colo-compare.h |  1 +
>  softmmu/vl.c       |  2 ++
>  3 files changed, 32 insertions(+), 6 deletions(-)
> 
> diff --git a/net/colo-compare.c b/net/colo-compare.c index
> 56db3d3bfc..c7572d75e9 100644
> --- a/net/colo-compare.c
> +++ b/net/colo-compare.c
> @@ -54,6 +54,8 @@ static NotifierList colo_compare_notifiers =  #define
> REGULAR_PACKET_CHECK_MS 3000  #define DEFAULT_TIME_OUT_MS 3000
> 
> +static QemuMutex colo_compare_mutex;
> +static bool colo_compare_active;
>  static QemuMutex event_mtx;
>  static QemuCond event_complete_cond;
>  static int event_unhandled_count;
> @@ -906,6 +908,12 @@ static void check_old_packet_regular(void *opaque)
> void colo_notify_compares_event(void *opaque, int event, Error **errp)  {
>      CompareState *s;
> +    qemu_mutex_lock(&colo_compare_mutex);
> +
> +    if (!colo_compare_active) {
> +        qemu_mutex_unlock(&colo_compare_mutex);
> +        return;
> +    }
> 
>      qemu_mutex_lock(&event_mtx);
>      QTAILQ_FOREACH(s, &net_compares, next) { @@ -919,6 +927,7 @@ void
> colo_notify_compares_event(void *opaque, int event, Error **errp)
>      }
> 
>      qemu_mutex_unlock(&event_mtx);
> +    qemu_mutex_unlock(&colo_compare_mutex);
>  }
> 
>  static void colo_compare_timer_init(CompareState *s) @@ -1274,7 +1283,14
> @@ static void colo_compare_complete(UserCreatable *uc, Error **errp)
>                             s->vnet_hdr);
>      }
> 
> +    qemu_mutex_lock(&colo_compare_mutex);
> +    if (!colo_compare_active) {
> +        qemu_mutex_init(&event_mtx);
> +        qemu_cond_init(&event_complete_cond);
> +        colo_compare_active = true;
> +    }
>      QTAILQ_INSERT_TAIL(&net_compares, s, next);
> +    qemu_mutex_unlock(&colo_compare_mutex);
> 
>      s->out_sendco.s = s;
>      s->out_sendco.chr = &s->chr_out;
> @@ -1290,9 +1306,6 @@ static void colo_compare_complete(UserCreatable
> *uc, Error **errp)
> 
>      g_queue_init(&s->conn_list);
> 
> -    qemu_mutex_init(&event_mtx);
> -    qemu_cond_init(&event_complete_cond);
> -
>      s->connection_track_table =
> g_hash_table_new_full(connection_key_hash,
>                                                        connection_key_equal,
>                                                        g_free, @@ -1384,12 +1397,19 @@ static void
> colo_compare_finalize(Object *obj)
> 
>      qemu_bh_delete(s->event_bh);
> 
> +    qemu_mutex_lock(&colo_compare_mutex);
>      QTAILQ_FOREACH(tmp, &net_compares, next) {
>          if (tmp == s) {
>              QTAILQ_REMOVE(&net_compares, s, next);
>              break;
>          }
>      }
> +    if (QTAILQ_EMPTY(&net_compares)) {
> +        colo_compare_active = false;
> +        qemu_mutex_destroy(&event_mtx);
> +        qemu_cond_destroy(&event_complete_cond);
> +    }
> +    qemu_mutex_unlock(&colo_compare_mutex);
> 
>      AioContext *ctx = iothread_get_aio_context(s->iothread);
>      aio_context_acquire(ctx);
> @@ -1413,15 +1433,18 @@ static void colo_compare_finalize(Object *obj)
>          object_unref(OBJECT(s->iothread));
>      }
> 
> -    qemu_mutex_destroy(&event_mtx);
> -    qemu_cond_destroy(&event_complete_cond);
> -
>      g_free(s->pri_indev);
>      g_free(s->sec_indev);
>      g_free(s->outdev);
>      g_free(s->notify_dev);
>  }
> 
> +void colo_compare_init_globals(void)
> +{
> +    colo_compare_active = false;
> +    qemu_mutex_init(&colo_compare_mutex);
> +}
> +
>  static const TypeInfo colo_compare_info = {
>      .name = TYPE_COLO_COMPARE,
>      .parent = TYPE_OBJECT,
> diff --git a/net/colo-compare.h b/net/colo-compare.h index
> 22ddd512e2..eb483ac586 100644
> --- a/net/colo-compare.h
> +++ b/net/colo-compare.h
> @@ -17,6 +17,7 @@
>  #ifndef QEMU_COLO_COMPARE_H
>  #define QEMU_COLO_COMPARE_H
> 
> +void colo_compare_init_globals(void);
>  void colo_notify_compares_event(void *opaque, int event, Error **errp);
> void colo_compare_register_notifier(Notifier *notify);  void
> colo_compare_unregister_notifier(Notifier *notify); diff --git a/softmmu/vl.c
> b/softmmu/vl.c index 32c0047889..a913ed5469 100644
> --- a/softmmu/vl.c
> +++ b/softmmu/vl.c
> @@ -112,6 +112,7 @@
>  #include "qapi/qmp/qerror.h"
>  #include "sysemu/iothread.h"
>  #include "qemu/guest-random.h"
> +#include "net/colo-compare.h"
> 
>  #define MAX_VIRTIO_CONSOLES 1
> 
> @@ -2906,6 +2907,7 @@ void qemu_init(int argc, char **argv, char **envp)
>      precopy_infrastructure_init();
>      postcopy_infrastructure_init();
>      monitor_init_globals();
> +    colo_compare_init_globals();
> 
>      if (qcrypto_init(&err) < 0) {
>          error_reportf_err(err, "cannot initialize crypto: ");
> --
> 2.20.1