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Re: [Qemu-devel] [PATCH v2 5/6] monitor: prevent inserting new monitors
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] [PATCH v2 5/6] monitor: prevent inserting new monitors after cleanup |
Date: |
Mon, 03 Dec 2018 09:59:08 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) |
Marc-André Lureau <address@hidden> writes:
> 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 <address@hidden>
The commit message explains what the patch does, but not why we want to
do it.
> ---
> monitor.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/monitor.c b/monitor.c
> index fffeb27ef9..7fe89daa87 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;
> @@ -4536,8 +4537,16 @@ 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);
> + 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)
> @@ -4631,6 +4640,7 @@ 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);
monitor_cleanup() is one of the last things main() calls before it
returns. If another thread creates a monitor afterwards, it won't be
cleaned up. I figure that's the reason we want this patch. There might
be more serious issues than failure to clean up. Please explain in your
commit message.
monitor_list_append() is called by monitor_init(), either directly right
before it returns, or via a bottom half if mon->use_io_thread.
Therefore, @monitor_destroyed can only be true if monitor_init()
commonly runs in a thread other than the main thread. Please give an
example where it does, in your commit message.
- Re: [Qemu-devel] [PATCH v2 5/6] monitor: prevent inserting new monitors after cleanup,
Markus Armbruster <=