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?
> 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;
>
>
