Marc-André Lureau <marcandre.lur...@redhat.com> writes:
> monitor_cleanup() is one of the last things main() calls before it
> returns. In the following patch, monitor_cleanup() will release the
> monitor_lock during flushing. There may be pending commands to insert
> new monitors, which would modify the mon_list during iteration, and
> the clean-up could thus miss those new insertions.
>
> Add a monitor_destroyed global to check if monitor_cleanup() has been
> already called. In this case, don't insert the new monitor in the
> list, but free it instead.
>
> Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
> ---
> monitor.c | 19 +++++++++++++++++--
> 1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/monitor.c b/monitor.c
> index 25cf4223e8..f0256bdec5 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -263,10 +263,11 @@ typedef struct QMPRequest QMPRequest;
> /* QMP checker flags */
> #define QMP_ACCEPT_UNKNOWNS 1
>
> -/* Protects mon_list, monitor_qapi_event_state. */
> +/* Protects mon_list, monitor_qapi_event_state, monitor_destroyed. */
> static QemuMutex monitor_lock;
> static GHashTable *monitor_qapi_event_state;
> static QTAILQ_HEAD(mon_list, Monitor) mon_list;
> +static bool monitor_destroyed;
>
> /* Protects mon_fdsets */
> static QemuMutex mon_fdsets_lock;
> @@ -4538,8 +4539,21 @@ void error_vprintf_unless_qmp(const char *fmt, va_list
> ap)
> static void monitor_list_append(Monitor *mon)
> {
> qemu_mutex_lock(&monitor_lock);
> - QTAILQ_INSERT_HEAD(&mon_list, mon, entry);
> + /*
> + * This prevents inserting new monitors during monitor_cleanup().
> + * A cleaner solution would involve the main thread telling other
> + * threads to terminate, waiting for their termination.
Let's add this sentence to the commit message as well.
> + */
> + if (!monitor_destroyed) {
> + QTAILQ_INSERT_HEAD(&mon_list, mon, entry);
> + mon = NULL;
> + }
> qemu_mutex_unlock(&monitor_lock);
> +
> + if (mon) {
> + monitor_data_destroy(mon);
> + g_free(mon);
> + }
> }
>
> static void monitor_qmp_setup_handlers_bh(void *opaque)
> @@ -4635,6 +4649,7 @@ void monitor_cleanup(void)
>
> /* Flush output buffers and destroy monitors */
> qemu_mutex_lock(&monitor_lock);
> + monitor_destroyed = true;
> QTAILQ_FOREACH_SAFE(mon, &mon_list, entry, next) {
> QTAILQ_REMOVE(&mon_list, mon, entry);
> monitor_flush(mon);
Reviewed-by: Markus Armbruster <arm...@redhat.com>
