util/main-loop.c | 24 +++++++++++++----------- 1 file changed, 13 insertions(+), 11 deletions(-)
A common pattern is seen where a timer fires, the callback does some
work, then rearms the timer which implicitly calls qemu_notify_event().
qemu_notify_event() is supposed to interrupt the main loop's poll() by
calling qemu_bh_schedule(). In the case that this is being called from a
main loop callback, the main loop is already not waiting on poll() and
instead it means the main loop does an addition iteration with a timeout
of 0 to handle the bottom half wakeup, before once again polling with
the expected timeout value.
Detect this situation by skipping the qemu_bh_schedule() call if the
default main context is currently owned by the caller. i.e. it is being
called as part of a poll / timer callback. Adjust the scope of the main
context acquire / release to cover the timer callbacks in
qemu_clock_run_all_timers().
Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
---
util/main-loop.c | 24 +++++++++++++-----------
1 file changed, 13 insertions(+), 11 deletions(-)
diff --git a/util/main-loop.c b/util/main-loop.c
index a0386cfeb60c..a2afbb7d0e13 100644
--- a/util/main-loop.c
+++ b/util/main-loop.c
@@ -145,10 +145,16 @@ AioContext *qemu_get_aio_context(void)
void qemu_notify_event(void)
{
+ GMainContext *context;
+
if (!qemu_aio_context) {
return;
}
- qemu_bh_schedule(qemu_notify_bh);
+
+ context = g_main_context_default();
+ if (!g_main_context_is_owner(context)) {
+ qemu_bh_schedule(qemu_notify_bh);
+ }
}
static GArray *gpollfds;
@@ -292,11 +298,8 @@ static void glib_pollfds_poll(void)
static int os_host_main_loop_wait(int64_t timeout)
{
- GMainContext *context = g_main_context_default();
int ret;
- g_main_context_acquire(context);
-
glib_pollfds_fill(&timeout);
bql_unlock();
@@ -309,8 +312,6 @@ static int os_host_main_loop_wait(int64_t timeout)
glib_pollfds_poll();
- g_main_context_release(context);
-
return ret;
}
#else
@@ -470,15 +471,12 @@ static int os_host_main_loop_wait(int64_t timeout)
fd_set rfds, wfds, xfds;
int nfds;
- g_main_context_acquire(context);
-
/* XXX: need to suppress polling by better using win32 events */
ret = 0;
for (pe = first_polling_entry; pe != NULL; pe = pe->next) {
ret |= pe->func(pe->opaque);
}
if (ret != 0) {
- g_main_context_release(context);
return ret;
}
@@ -538,8 +536,6 @@ static int os_host_main_loop_wait(int64_t timeout)
g_main_context_dispatch(context);
}
- g_main_context_release(context);
-
return select_ret || g_poll_ret;
}
#endif
@@ -559,6 +555,7 @@ void main_loop_poll_remove_notifier(Notifier *notify)
void main_loop_wait(int nonblocking)
{
+ GMainContext *context = g_main_context_default();
MainLoopPoll mlpoll = {
.state = MAIN_LOOP_POLL_FILL,
.timeout = UINT32_MAX,
@@ -586,7 +583,10 @@ void main_loop_wait(int nonblocking)
timerlistgroup_deadline_ns(
&main_loop_tlg));
+ g_main_context_acquire(context);
+
ret = os_host_main_loop_wait(timeout_ns);
+
mlpoll.state = ret < 0 ? MAIN_LOOP_POLL_ERR : MAIN_LOOP_POLL_OK;
notifier_list_notify(&main_loop_poll_notifiers, &mlpoll);
@@ -598,6 +598,8 @@ void main_loop_wait(int nonblocking)
icount_start_warp_timer();
}
qemu_clock_run_all_timers();
+
+ g_main_context_release(context);
}
/* Functions to operate on the main QEMU AioContext. */
--
2.43.0
On Mon, Feb 12, 2024 at 11:45 AM Ross Lagerwall <ross.lagerwall@citrix.com> wrote: > > A common pattern is seen where a timer fires, the callback does some > work, then rearms the timer which implicitly calls qemu_notify_event(). > > qemu_notify_event() is supposed to interrupt the main loop's poll() by > calling qemu_bh_schedule(). In the case that this is being called from a > main loop callback, the main loop is already not waiting on poll() and > instead it means the main loop does an addition iteration with a timeout > of 0 to handle the bottom half wakeup, before once again polling with > the expected timeout value. > > Detect this situation by skipping the qemu_bh_schedule() call if the > default main context is currently owned by the caller. i.e. it is being > called as part of a poll / timer callback. Adjust the scope of the main > context acquire / release to cover the timer callbacks in > qemu_clock_run_all_timers(). > > Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com> > --- > util/main-loop.c | 24 +++++++++++++----------- > 1 file changed, 13 insertions(+), 11 deletions(-) > > diff --git a/util/main-loop.c b/util/main-loop.c > index a0386cfeb60c..a2afbb7d0e13 100644 > --- a/util/main-loop.c > +++ b/util/main-loop.c > @@ -145,10 +145,16 @@ AioContext *qemu_get_aio_context(void) > > void qemu_notify_event(void) > { > + GMainContext *context; > + > if (!qemu_aio_context) { > return; > } > - qemu_bh_schedule(qemu_notify_bh); > + > + context = g_main_context_default(); > + if (!g_main_context_is_owner(context)) { > + qemu_bh_schedule(qemu_notify_bh); > + } > } > > static GArray *gpollfds; > @@ -292,11 +298,8 @@ static void glib_pollfds_poll(void) > > static int os_host_main_loop_wait(int64_t timeout) > { > - GMainContext *context = g_main_context_default(); > int ret; > > - g_main_context_acquire(context); > - > glib_pollfds_fill(&timeout); > > bql_unlock(); > @@ -309,8 +312,6 @@ static int os_host_main_loop_wait(int64_t timeout) > > glib_pollfds_poll(); > > - g_main_context_release(context); > - > return ret; > } > #else > @@ -470,15 +471,12 @@ static int os_host_main_loop_wait(int64_t timeout) > fd_set rfds, wfds, xfds; > int nfds; > > - g_main_context_acquire(context); > - > /* XXX: need to suppress polling by better using win32 events */ > ret = 0; > for (pe = first_polling_entry; pe != NULL; pe = pe->next) { > ret |= pe->func(pe->opaque); > } > if (ret != 0) { > - g_main_context_release(context); > return ret; > } > > @@ -538,8 +536,6 @@ static int os_host_main_loop_wait(int64_t timeout) > g_main_context_dispatch(context); > } > > - g_main_context_release(context); > - > return select_ret || g_poll_ret; > } > #endif > @@ -559,6 +555,7 @@ void main_loop_poll_remove_notifier(Notifier *notify) > > void main_loop_wait(int nonblocking) > { > + GMainContext *context = g_main_context_default(); > MainLoopPoll mlpoll = { > .state = MAIN_LOOP_POLL_FILL, > .timeout = UINT32_MAX, > @@ -586,7 +583,10 @@ void main_loop_wait(int nonblocking) > timerlistgroup_deadline_ns( > &main_loop_tlg)); > > + g_main_context_acquire(context); > + > ret = os_host_main_loop_wait(timeout_ns); > + > mlpoll.state = ret < 0 ? MAIN_LOOP_POLL_ERR : MAIN_LOOP_POLL_OK; > notifier_list_notify(&main_loop_poll_notifiers, &mlpoll); > > @@ -598,6 +598,8 @@ void main_loop_wait(int nonblocking) > icount_start_warp_timer(); > } > qemu_clock_run_all_timers(); > + > + g_main_context_release(context); > } > > /* Functions to operate on the main QEMU AioContext. */ > -- > 2.43.0 > Ping? Ross
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