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

[Lukas Straub <lukasstraub2@web.de>]

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On Thu, 7 May 2020 11:38:04 +0000
"Zhang, Chen" <chen.zhang@intel.com> wrote:

> > -----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.

Yeah, but that still leaves the other problem that colo can't be used without colo-compare (qemu crashes then).

Regards,
Lukas Straub

> 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  
> 


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