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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

17
balloon.c
View file

@ -32,30 +32,33 @@
static QEMUBalloonEvent *balloon_event_fn;
static QEMUBalloonStatus *balloon_stat_fn;
static void *balloon_opaque;
void qemu_add_balloon_handler(QEMUBalloonEvent *func, void *opaque)
void qemu_add_balloon_handler(QEMUBalloonEvent *event_func,
QEMUBalloonStatus *stat_func, void *opaque)
{
balloon_event_fn = func;
balloon_event_fn = event_func;
balloon_stat_fn = stat_func;
balloon_opaque = opaque;
}
static int qemu_balloon(ram_addr_t target, MonitorCompletion cb, void *opaque)
static int qemu_balloon(ram_addr_t target)
{
if (!balloon_event_fn) {
return 0;
}
trace_balloon_event(balloon_opaque, target);
balloon_event_fn(balloon_opaque, target, cb, opaque);
balloon_event_fn(balloon_opaque, target);
return 1;
}
static int qemu_balloon_status(MonitorCompletion cb, void *opaque)
{
if (!balloon_event_fn) {
if (!balloon_stat_fn) {
return 0;
}
balloon_event_fn(balloon_opaque, 0, cb, opaque);
balloon_stat_fn(balloon_opaque, cb, opaque);
return 1;
}
@ -135,7 +138,7 @@ int do_balloon(Monitor *mon, const QDict *params,
return -1;
}
ret = qemu_balloon(qdict_get_int(params, "value"), cb, opaque);
ret = qemu_balloon(qdict_get_int(params, "value"));
if (ret == 0) {
qerror_report(QERR_DEVICE_NOT_ACTIVE, "balloon");
return -1;