| Message ID | 20181029125733.14597-6-marcandre.lureau@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | monitor: misc fixes | expand |
On Mon, Oct 29, 2018 at 04:57:32PM +0400, Marc-André Lureau wrote: > 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. Pure question: how to trigger the condition when doing monitor cleanups? I can understand the problem to be fixed in the follow-up patch, but I don't know whether it's that helpful to have this patch though, especially considering that we're reaching softfreeze. > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com> > --- > 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); > -- > 2.19.0.271.gfe8321ec05 > Regards,
Marc-André Lureau <marcandre.lureau@redhat.com> 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 <marcandre.lureau@redhat.com> 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.
Hi On Mon, Dec 3, 2018 at 12:59 PM Markus Armbruster <armbru@redhat.com> wrote: > > Marc-André Lureau <marcandre.lureau@redhat.com> 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 <marcandre.lureau@redhat.com> > > 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. Is this clearer? 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. > 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.
Marc-André Lureau <marcandre.lureau@redhat.com> writes: > Hi > On Mon, Dec 3, 2018 at 12:59 PM Markus Armbruster <armbru@redhat.com> wrote: >> >> Marc-André Lureau <marcandre.lureau@redhat.com> 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 <marcandre.lureau@redhat.com> >> >> 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. > > Is this clearer? > > 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. Yes. The solution feels a bit clunky: it duplicates part of the work monitor_cleanup() does into monitor_list_append(). Works because the part it doesn't duplicate needn't be done in this case: removing from @mon_list, and monitor_flush(). I suspect a cleaner solution would involve the main thread telling other threads to terminate, waiting for their termination with pthread_join(), and only then do final cleanup. I'm not asking for that solution now. A clunky fix we have is better than a refactoring we don't have. A comment admitting the clunkiness would be nice. >> 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.
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);
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.lureau@redhat.com> --- monitor.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-)