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monitor: prevent inserting new monitors after cleanup

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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. A cleaner solution would involve the main
thread telling other threads to terminate, waiting for their
termination.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20181205203737.9011-7-marcandre.lureau@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
This commit is contained in:
Marc-André Lureau 2018-12-06 00:37:36 +04:00 committed by Markus Armbruster
parent 269d25cdeb
commit 8dac00bbfb
1 changed files with 17 additions and 2 deletions
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19
monitor.c
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@ -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.
*/
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)
@ -4634,6 +4648,7 @@ 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);