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tests/iothread: Always connect iothread GSource to a GMainContext

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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 <peter.maydell@linaro.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-id: 20200106144552.7205-1-peter.maydell@linaro.org
This commit is contained in:
Peter Maydell 2020-01-06 14:45:52 +00:00
parent a8f2c60cef
commit 0cb0406172
1 changed files with 30 additions and 0 deletions
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30
tests/iothread.c
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@ -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);