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[PATCH] tests/iothread: Always connect iothread GSource to a GMainContex
From: |
Peter Maydell |
Subject: |
[PATCH] tests/iothread: Always connect iothread GSource to a GMainContext |
Date: |
Mon, 6 Jan 2020 14:45:52 +0000 |
On older versions of glib (anything prior to glib commit 0f056ebe
from May 2019), the implementation of g_source_ref() and
g_source_unref() is not threadsafe for a GSource which is not
attached to a GMainContext.
QEMU's real iothread.c implementation always attaches its
iothread->ctx's GSource to a GMainContext created for that iothread,
so it is OK, but the simple test framework implementation in
tests/iothread.c was not doing this. This was causing intermittent
assertion failures in the test-aio-multithread subtest
"/aio/multi/mutex/contended" test on the BSD hosts. (It's unclear
why only BSD seems to have been affected -- perhaps a combination of
the specific glib version being used in the VMs and their happening
to run on a host with a lot of CPUs).
Borrow the iothread_init_gcontext() from the real iothread.c
and add the corresponding cleanup code and the calls to
g_main_context_push/pop_thread_default() so we actually use
the GMainContext we create.
Signed-off-by: Peter Maydell <address@hidden>
---
I don't really have a good understanding of the glib APIs here,
so I'm mostly just cribbing code from the real iothread.c;
review by people who do know the glib/iothread stuff better
welcomed. It does seem to fix the intermittent test failure
on NetBSD, at least, where we were running into an assertion
failure because a g_source_unref() incorrectly thought it
had decremented the refcount to 0 and should delete a context
that was actually still in use.
tests/iothread.c | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)
diff --git a/tests/iothread.c b/tests/iothread.c
index 13c9fdcd8df..d3a2ee9a014 100644
--- a/tests/iothread.c
+++ b/tests/iothread.c
@@ -21,6 +21,8 @@
struct IOThread {
AioContext *ctx;
+ GMainContext *worker_context;
+ GMainLoop *main_loop;
QemuThread thread;
QemuMutex init_done_lock;
@@ -35,6 +37,17 @@ AioContext *qemu_get_current_aio_context(void)
return my_iothread ? my_iothread->ctx : qemu_get_aio_context();
}
+static void iothread_init_gcontext(IOThread *iothread)
+{
+ GSource *source;
+
+ iothread->worker_context = g_main_context_new();
+ source = aio_get_g_source(iothread_get_aio_context(iothread));
+ g_source_attach(source, iothread->worker_context);
+ g_source_unref(source);
+ iothread->main_loop = g_main_loop_new(iothread->worker_context, TRUE);
+}
+
static void *iothread_run(void *opaque)
{
IOThread *iothread = opaque;
@@ -44,6 +57,20 @@ static void *iothread_run(void *opaque)
my_iothread = iothread;
qemu_mutex_lock(&iothread->init_done_lock);
iothread->ctx = aio_context_new(&error_abort);
+
+ /*
+ * We must connect the ctx to a GMainContext, because in older versions
+ * of glib the g_source_ref()/unref() functions are not threadsafe
+ * on sources without a context.
+ */
+ iothread_init_gcontext(iothread);
+
+ /*
+ * g_main_context_push_thread_default() must be called before anything
+ * in this new thread uses glib.
+ */
+ g_main_context_push_thread_default(iothread->worker_context);
+
qemu_cond_signal(&iothread->init_done_cond);
qemu_mutex_unlock(&iothread->init_done_lock);
@@ -51,6 +78,7 @@ static void *iothread_run(void *opaque)
aio_poll(iothread->ctx, true);
}
+ g_main_context_pop_thread_default(iothread->worker_context);
rcu_unregister_thread();
return NULL;
}
@@ -66,6 +94,8 @@ void iothread_join(IOThread *iothread)
{
aio_bh_schedule_oneshot(iothread->ctx, iothread_stop_bh, iothread);
qemu_thread_join(&iothread->thread);
+ g_main_context_unref(iothread->worker_context);
+ g_main_loop_unref(iothread->main_loop);
qemu_cond_destroy(&iothread->init_done_cond);
qemu_mutex_destroy(&iothread->init_done_lock);
aio_context_unref(iothread->ctx);
--
2.20.1
- [PATCH] tests/iothread: Always connect iothread GSource to a GMainContext,
Peter Maydell <=