On Fri, 13 Oct 2017 11:24:59 +0200
Igor Mammedov <imamm...@redhat.com> wrote:
> On Fri, 13 Oct 2017 10:35:31 +0200
> Greg Kurz <gr...@kaod.org> wrote:
>
> > If a CPU selected with the "cpu" command is hot-unplugged then "info cpus"
> > causes QEMU to exit:
> >
> > (qemu) device_del cpu1
> > (qemu) info cpus
> > qemu:qemu_cpu_kick_thread: No such process
> >
> > This happens because "cpu" stores the pointer to the selected CPU into
> > the monitor structure. When the CPU is hot-unplugged, we end up with a
> > dangling pointer. The "info cpus" command then does:
> >
> > hmp_info_cpus()
> > monitor_get_cpu_index()
> > mon_get_cpu()
> > cpu_synchronize_state() <--- called with dangling pointer
> >
> > This could cause a QEMU crash as well.
> >
> > This patch switches the monitor to use object_ref() to ensure the
> > CPU object doesn't vanish unexpectedly. The reference is dropped
> > either when "cpu" is used to switch to another CPU, or when the
> > selected CPU is unrealized and cpu_list_remove() sets its cpu_index
> > back to UNASSIGNED_CPU_INDEX.
> I don't really like an idea of leaving dangling cpu around.
> Is it possible to store QOM path on set_cpu in monitor and
> resolving it each to instance each time it's needed?
>
It sounds workable. Also it would allow the fix to not depend on patch 1
for ppc.
Thanks for the suggestion!
>
> > Signed-off-by: Greg Kurz <gr...@kaod.org>
> > ---
> > monitor.c | 12 ++++++++++++
> > 1 file changed, 12 insertions(+)
> >
> > diff --git a/monitor.c b/monitor.c
> > index fe0d1bdbb461..1c0b9a2c3ad3 100644
> > --- a/monitor.c
> > +++ b/monitor.c
> > @@ -579,6 +579,9 @@ static void monitor_data_init(Monitor *mon)
> >
> > static void monitor_data_destroy(Monitor *mon)
> > {
> > + if (mon->mon_cpu) {
> > + object_unref((Object *) mon->mon_cpu);
> > + }
> > qemu_chr_fe_deinit(&mon->chr, false);
> > if (monitor_is_qmp(mon)) {
> > json_message_parser_destroy(&mon->qmp.parser);
> > @@ -1047,12 +1050,21 @@ int monitor_set_cpu(int cpu_index)
> > if (cpu == NULL) {
> > return -1;
> > }
> > + if (cur_mon->mon_cpu) {
> > + object_unref((Object *) cur_mon->mon_cpu);
> > + }
> > cur_mon->mon_cpu = cpu;
> > + object_ref((Object *) cpu);
> > return 0;
> > }
> >
> > CPUState *mon_get_cpu(void)
> > {
> > + if (cur_mon->mon_cpu &&
> > + cur_mon->mon_cpu->cpu_index == UNASSIGNED_CPU_INDEX) {
> > + object_unref((Object *) cur_mon->mon_cpu);
> > + cur_mon->mon_cpu = NULL;
> > + }
> > if (!cur_mon->mon_cpu) {
> > if (!first_cpu) {
> > return NULL;
> >
> >
>
