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balloon: Separate out stat and balloon handling

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Passing on '0' as ballooning target to indicate retrieval of stats is
bad API.  It also makes 'balloon 0' in the monitor cause a segfault.
Have two different functions handle the different functionality instead.

Detailed explanation from Markus's review:

1. do_info_balloon() is an info_async() method.  It receives a callback
   with argument, to be called exactly once (callback frees the
   argument).  It passes the callback via qemu_balloon_status() and
   indirectly through qemu_balloon_event to virtio_balloon_to_target().

   virtio_balloon_to_target() executes its balloon stats half.  It
   stores the callback in the device state.

   If it can't send a stats request, it resets stats and calls the
   callback right away.

   Else, it sends a stats request.  The device model runs the callback
   when it receives the answer.

   Works.

2. do_balloon() is a cmd_async() method.  It receives a callback with
   argument, to be called when the command completes.  do_balloon()
   calls it right before it succeeds.  Odd, but should work.

   Nevertheless, it passes the callback on via qemu_ballon() and
   indirectly through qemu_balloon_event to virtio_balloon_to_target().

   a. If the argument is non-zero, virtio_balloon_to_target() executes
      its balloon half, which doesn't use the callback in any way.

      Odd, but works.

   b. If the argument is zero, virtio_balloon_to_target() executes its
      balloon stats half, just like in 1.  It either calls the callback
      right away, or arranges for it to be called later.

      Thus, the callback runs twice: use after free and double free.

Test case: start with -S -device virtio-balloon, execute "balloon 0" in
human monitor.  Runs the callback first from virtio_balloon_to_target(),
then again from do_balloon().

Reported-by: Mike Cao <bcao@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
This commit is contained in:
Amit Shah 2011-07-20 13:30:56 +05:30 • committed by Anthony Liguori
parent dce911c753
commit 30fb2ca603
3 changed files with 17 additions and 15 deletions
Download patch file Download diff file Expand all files Collapse all files

7
hw/virtio-balloon.c
View file

@ -227,8 +227,7 @@ static void virtio_balloon_stat(void *opaque, MonitorCompletion cb,
complete_stats_request(dev);
}
static void virtio_balloon_to_target(void *opaque, ram_addr_t target,
MonitorCompletion cb, void *cb_data)
static void virtio_balloon_to_target(void *opaque, ram_addr_t target)
{
VirtIOBalloon *dev = opaque;
@ -238,8 +237,6 @@ static void virtio_balloon_to_target(void *opaque, ram_addr_t target,
if (target) {
dev->num_pages = (ram_size - target) >> VIRTIO_BALLOON_PFN_SHIFT;
virtio_notify_config(&dev->vdev);
} else {
virtio_balloon_stat(opaque, cb, cb_data);
}
}
@ -284,7 +281,7 @@ VirtIODevice *virtio_balloon_init(DeviceState *dev)
s->svq = virtio_add_queue(&s->vdev, 128, virtio_balloon_receive_stats);
reset_stats(s);
qemu_add_balloon_handler(virtio_balloon_to_target, s);
qemu_add_balloon_handler(virtio_balloon_to_target, virtio_balloon_stat, s);
register_savevm(dev, "virtio-balloon", -1, 1,
virtio_balloon_save, virtio_balloon_load, s);