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Re: [Qemu-devel] [PATCH] AioContext: fix broken ctx->dispatching optimiz
From: |
Laszlo Ersek |
Subject: |
Re: [Qemu-devel] [PATCH] AioContext: fix broken ctx->dispatching optimization |
Date: |
Wed, 15 Jul 2015 20:00:45 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 |
comments below
On 07/15/15 19:13, Paolo Bonzini wrote:
> This patch rewrites the ctx->dispatching optimization, which was the cause
> of some mysterious hangs that could be reproduced on aarch64 KVM only.
> The hangs were indirectly caused by aio_poll() and in particular by
> flash memory updates's call to blk_write(), which invokes aio_poll().
> Fun stuff: they had an extremely short race window, so much that
> adding all kind of tracing to either the kernel or QEMU made it
> go away (a single printf made it half as reproducible).
>
> On the plus side, the failure mode (a hang until the next keypress)
> made it very easy to examine the state of the process with a debugger.
> And there was a very nice reproducer from Laszlo, which failed pretty
> often (more than half of the time) on any version of QEMU with a non-debug
> kernel; it also failed fast, while still in the firmware. So, it could
> have been worse.
>
> For some unknown reason they happened only with virtio-scsi, but
> that's not important. It's more interesting that they disappeared with
> io=native, making thread-pool.c a likely suspect for where the bug arose.
> thread-pool.c is also one of the few places which use bottom halves
> across threads, by the way.
>
> I hope that no other similar bugs exist, but just in case :) I am
> going to describe how the successful debugging went... Since the
> likely culprit was the ctx->dispatching optimization, which mostly
> affects bottom halves, the first observation was that there are two
> qemu_bh_schedule() invocations in the thread pool: the one in the aio
> worker and the one in thread_pool_completion_bh. The latter always
> causes the optimization to trigger, the former may or may not. In
> order to restrict the possibilities, I introduced new functions
> qemu_bh_schedule_slow() and qemu_bh_schedule_fast():
>
> /* qemu_bh_schedule_slow: */
> ctx = bh->ctx;
> bh->idle = 0;
> if (atomic_xchg(&bh->scheduled, 1) == 0) {
> event_notifier_set(&ctx->notifier);
> }
>
> /* qemu_bh_schedule_fast: */
> ctx = bh->ctx;
> bh->idle = 0;
> assert(ctx->dispatching);
> atomic_xchg(&bh->scheduled, 1);
>
> Notice how the atomic_xchg is still in qemu_bh_schedule_slow(). This
> was already debated a few months ago, so I assumed it to be correct.
> In retrospect this was a very good idea, as you'll see later.
>
> Changing thread_pool_completion_bh() to qemu_bh_schedule_fast() didn't
> trigger the assertion (as expected). Changing the worker's invocation
> to qemu_bh_schedule_slow() didn't hide the bug (another assumption
> which luckily held). This already limited heavily the amount of
> interaction between the threads, hinting that the problematic events
> must have triggered around thread_pool_completion_bh().
>
> As mentioned early, invoking a debugger to examine the state of a
> hung process was pretty easy; the iothread was always waiting on a
> poll(..., -1) system call. Infinite timeouts are much rarer on x86,
> and this could be the reason why the bug was never observed there.
> With the buggy sequence more or less resolved to an interaction between
> thread_pool_completion_bh() and poll(..., -1), my "tracing" strategy was
> to just add a few qemu_clock_get_ns(QEMU_CLOCK_REALTIME) calls, hoping
> that the ordering of aio_ctx_prepare(), aio_ctx_dispatch, poll() and
> qemu_bh_schedule_fast() would provide some hint. The output was:
>
> (gdb) p last_prepare
> $3 = 103885451
> (gdb) p last_dispatch
> $4 = 103876492
> (gdb) p last_poll
> $5 = 115909333
> (gdb) p last_schedule
> $6 = 115925212
>
> Notice how the last call to qemu_poll_ns() came after aio_ctx_dispatch().
> This makes little sense unless there is an aio_poll() call involved,
> and indeed with a slightly different instrumentation you can see that
> there is one:
>
> (gdb) p last_prepare
> $3 = 107569679
> (gdb) p last_dispatch
> $4 = 107561600
> (gdb) p last_aio_poll
> $5 = 110671400
> (gdb) p last_schedule
> $6 = 110698917
>
> So the scenario becomes clearer:
>
> iothread VCPU thread
> --------------------------------------------------------------------------
> aio_ctx_prepare
> aio_ctx_check
> qemu_poll_ns(timeout=-1)
> aio_poll
> aio_dispatch
> thread_pool_completion_bh
> qemu_bh_schedule()
>
> At this point bh->scheduled = 1 and the iothread has not been woken up.
> The solution must be close, but this alone should not be a problem,
> because the bottom half is only rescheduled to account for rare situations
> (see commit 3c80ca1, thread-pool: avoid deadlock in nested aio_poll()
> calls, 2014-07-15).
>
> Introducing a third thread---a thread pool worker thread, which
> also does qemu_bh_schedule()---does bring out the problematic case.
> The third thread must be awakened *after* the callback is complete and
> thread_pool_completion_bh has redone the whole loop, explaining the
> short race window. And then this is what happens:
>
> thread pool worker
> --------------------------------------------------------------------------
> <I/O completes>
> qemu_bh_schedule()
>
> Tada, bh->scheduled is already 1, so qemu_bh_schedule() does nothing
> and the iothread is never woken up. This is where the bh->scheduled
> optimization comes into play---it is correct, but removing it would
> have masked the bug.
>
> So, what is the bug?
>
> Well, the question asked by the ctx->dispatching optimization ("is any
> active aio_poll dispatching?") was wrong. The right question to ask
> instead is "is any active aio_poll *not* dispatching", i.e. in the prepare
> or poll phases? In that case, the aio_poll is sleeping or might go to
> sleep anytime soon, and the EventNotifier must be invoked to wake
> it up.
>
> In any other case (including if there is *no* active aio_poll at all!)
> we can just wait for the next prepare phase to pick up the event (e.g. a
> bottom half); the prepare phase will avoid the blocking and service the
> bottom half.
>
> Expressing the invariant with a logic formula, the broken one looked like:
>
> !(exists(thread): in_dispatching(thread)) => !optimize
>
> or equivalently:
>
> !(exists(thread):
> in_aio_poll(thread) && in_dispatching(thread)) => !optimize
>
> In the correct one, the negation is in a slightly different place:
>
> (exists(thread):
> in_aio_poll(thread) && !in_dispatching(thread)) => !optimize
>
> or equivalently:
>
> (exists(thread): in_prepare_or_poll(thread)) => !optimize
>
> Even if the difference boils down to moving an exclamation mark :)
> the implementation is quite different. However, I think the new
> one is simpler to understand.
>
> In the old implementation, the "exists" was implemented with a boolean
> value. This didn't really support well the case of multiple concurrent
> event loops, but I thought was that this was okay: aio_poll holds the
Absolutely stunning work. I hope others can review it in its full glory;
I don't know enough by far to do that. I'll just make two stupid comments:
- the first "was" in the last line above is superfluous,
- I'd prefer if the constants passed to the atomic primitives matched
the type of the "notify_me" field. The constants are "int", and the
field has type uint32_t. Admittedly, I don't know how GCC builtins
behave with regard to argument conversion; if they work just like
functions with visible prototypes, then it should be fine. (Yes, this
is an irrelevant comment. :))
Also I hope Rich can report back with some test results.
Acked-by: Laszlo Ersek <address@hidden>
Thank you.
Laszlo
> AioContext lock so there cannot be concurrent aio_poll invocations, and
> I was just considering nested event loops. However, aio_poll _could_
> indeed be concurrent with the GSource. This is why I came up with the
> wrong invariant.
>
> In the new implementation, "exists" is computed simply by counting how many
> threads are in the prepare or poll phases. There are some interesting
> points to consider, but the gist of the idea remains:
>
> 1) AioContext can be used through GSource as well; as mentioned in the
> patch, bit 0 of the counter is reserved for the GSource.
>
> 2) the counter need not be updated for a non-blocking aio_poll, because
> it won't sleep forever anyway. This is just a matter of checking
> the "blocking" variable. This requires some changes to the win32
> implementation, but is otherwise not too complicated.
>
> 3) as mentioned above, the new implementation will not call aio_notify
> when there is *no* active aio_poll at all. The tests have to be
> adjusted for this change. The calls to aio_notify in async.c are fine;
> they only want to kick aio_poll out of a blocking wait, but need not
> do anything if aio_poll is not running.
>
> 4) nested aio_poll: these just work with the new implementation; when
> a nested event loop is invoked, the outer event loop is never in the
> prepare or poll phases. The outer event loop thus has already decremented
> the counter.
>
> Reported-by: Richard W. M. Jones <address@hidden>
> Reported-by: Laszlo Ersek <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
> aio-posix.c | 19 ++++++------
> aio-win32.c | 33 ++++++++++-----------
> async.c | 21 +++++---------
> docs/aio_notify.promela | 77
> +++++++++++++++++++++----------------------------
> include/block/aio.h | 29 +++++++++++++++----
> tests/test-aio.c | 26 +++--------------
> 6 files changed, 91 insertions(+), 114 deletions(-)
>
> diff --git a/aio-posix.c b/aio-posix.c
> index 4abec38..268d14d 100644
> --- a/aio-posix.c
> +++ b/aio-posix.c
> @@ -233,26 +233,23 @@ static void add_pollfd(AioHandler *node)
> bool aio_poll(AioContext *ctx, bool blocking)
> {
> AioHandler *node;
> - bool was_dispatching;
> int i, ret;
> bool progress;
> int64_t timeout;
>
> aio_context_acquire(ctx);
> - was_dispatching = ctx->dispatching;
> progress = false;
>
> /* aio_notify can avoid the expensive event_notifier_set if
> * everything (file descriptors, bottom halves, timers) will
> * be re-evaluated before the next blocking poll(). This is
> * already true when aio_poll is called with blocking == false;
> - * if blocking == true, it is only true after poll() returns.
> - *
> - * If we're in a nested event loop, ctx->dispatching might be true.
> - * In that case we can restore it just before returning, but we
> - * have to clear it now.
> + * if blocking == true, it is only true after poll() returns,
> + * so disable the optimization now.
> */
> - aio_set_dispatching(ctx, !blocking);
> + if (blocking) {
> + atomic_add(&ctx->notify_me, 2);
> + }
>
> ctx->walking_handlers++;
>
> @@ -286,13 +283,15 @@ bool aio_poll(AioContext *ctx, bool blocking)
> npfd = 0;
> ctx->walking_handlers--;
>
> + if (blocking) {
> + atomic_sub(&ctx->notify_me, 2);
> + }
> +
> /* Run dispatch even if there were no readable fds to run timers */
> - aio_set_dispatching(ctx, true);
> if (aio_dispatch(ctx)) {
> progress = true;
> }
>
> - aio_set_dispatching(ctx, was_dispatching);
> aio_context_release(ctx);
>
> return progress;
> diff --git a/aio-win32.c b/aio-win32.c
> index 233d8f5..ae7c6cf 100644
> --- a/aio-win32.c
> +++ b/aio-win32.c
> @@ -279,30 +279,25 @@ bool aio_poll(AioContext *ctx, bool blocking)
> {
> AioHandler *node;
> HANDLE events[MAXIMUM_WAIT_OBJECTS + 1];
> - bool was_dispatching, progress, have_select_revents, first;
> + bool progress, have_select_revents, first;
> int count;
> int timeout;
>
> aio_context_acquire(ctx);
> - have_select_revents = aio_prepare(ctx);
> - if (have_select_revents) {
> - blocking = false;
> - }
> -
> - was_dispatching = ctx->dispatching;
> progress = false;
>
> /* aio_notify can avoid the expensive event_notifier_set if
> * everything (file descriptors, bottom halves, timers) will
> * be re-evaluated before the next blocking poll(). This is
> * already true when aio_poll is called with blocking == false;
> - * if blocking == true, it is only true after poll() returns.
> - *
> - * If we're in a nested event loop, ctx->dispatching might be true.
> - * In that case we can restore it just before returning, but we
> - * have to clear it now.
> + * if blocking == true, it is only true after poll() returns,
> + * so disable the optimization now.
> */
> - aio_set_dispatching(ctx, !blocking);
> + if (blocking) {
> + atomic_add(&ctx->notify_me, 2);
> + }
> +
> + have_select_revents = aio_prepare(ctx);
>
> ctx->walking_handlers++;
>
> @@ -318,11 +313,11 @@ bool aio_poll(AioContext *ctx, bool blocking)
> first = true;
>
> /* wait until next event */
> - while (count > 0) {
> + do {
> HANDLE event;
> int ret;
>
> - timeout = blocking
> + timeout = blocking && !have_select_revents
> ? qemu_timeout_ns_to_ms(aio_compute_timeout(ctx)) : 0;
> if (timeout) {
> aio_context_release(ctx);
> @@ -331,7 +326,10 @@ bool aio_poll(AioContext *ctx, bool blocking)
> if (timeout) {
> aio_context_acquire(ctx);
> }
> - aio_set_dispatching(ctx, true);
> + if (blocking) {
> + assert(first);
> + atomic_sub(&ctx->notify_me, 2);
> + }
>
> if (first && aio_bh_poll(ctx)) {
> progress = true;
> @@ -351,11 +349,10 @@ bool aio_poll(AioContext *ctx, bool blocking)
> blocking = false;
>
> progress |= aio_dispatch_handlers(ctx, event);
> - }
> + } while (count > 0);
>
> progress |= timerlistgroup_run_timers(&ctx->tlg);
>
> - aio_set_dispatching(ctx, was_dispatching);
> aio_context_release(ctx);
> return progress;
> }
> diff --git a/async.c b/async.c
> index 77d080d..a232192 100644
> --- a/async.c
> +++ b/async.c
> @@ -184,6 +184,8 @@ aio_ctx_prepare(GSource *source, gint *timeout)
> {
> AioContext *ctx = (AioContext *) source;
>
> + atomic_or(&ctx->notify_me, 1);
> +
> /* We assume there is no timeout already supplied */
> *timeout = qemu_timeout_ns_to_ms(aio_compute_timeout(ctx));
>
> @@ -200,6 +202,7 @@ aio_ctx_check(GSource *source)
> AioContext *ctx = (AioContext *) source;
> QEMUBH *bh;
>
> + atomic_and(&ctx->notify_me, ~1);
> for (bh = ctx->first_bh; bh; bh = bh->next) {
> if (!bh->deleted && bh->scheduled) {
> return true;
> @@ -254,23 +257,13 @@ ThreadPool *aio_get_thread_pool(AioContext *ctx)
> return ctx->thread_pool;
> }
>
> -void aio_set_dispatching(AioContext *ctx, bool dispatching)
> -{
> - ctx->dispatching = dispatching;
> - if (!dispatching) {
> - /* Write ctx->dispatching before reading e.g. bh->scheduled.
> - * Optimization: this is only needed when we're entering the "unsafe"
> - * phase where other threads must call event_notifier_set.
> - */
> - smp_mb();
> - }
> -}
> -
> void aio_notify(AioContext *ctx)
> {
> - /* Write e.g. bh->scheduled before reading ctx->dispatching. */
> + /* Write e.g. bh->scheduled before reading ctx->notify_me. Pairs
> + * with atomic_or in aio_ctx_prepare or atomic_add in aio_poll.
> + */
> smp_mb();
> - if (!ctx->dispatching) {
> + if (ctx->notify_me) {
> event_notifier_set(&ctx->notifier);
> }
> }
> diff --git a/docs/aio_notify.promela b/docs/aio_notify.promela
> index ad3f6f0..fccc7ee 100644
> --- a/docs/aio_notify.promela
> +++ b/docs/aio_notify.promela
> @@ -1,5 +1,5 @@
> /*
> - * This model describes the interaction between aio_set_dispatching()
> + * This model describes the interaction between ctx->notify_me
> * and aio_notify().
> *
> * Author: Paolo Bonzini <address@hidden>
> @@ -14,57 +14,53 @@
> * spin -a docs/aio_notify.promela
> * gcc -O2 pan.c
> * ./a.out -a
> + *
> + * To verify it (with a bug planted in the model):
> + * spin -a -DBUG docs/aio_notify.promela
> + * gcc -O2 pan.c
> + * ./a.out -a
> */
>
> #define MAX 4
> #define LAST (1 << (MAX - 1))
> #define FINAL ((LAST << 1) - 1)
>
> -bool dispatching;
> +bool notify_me;
> bool event;
>
> -int req, done;
> +int req;
> +int done;
>
> active proctype waiter()
> {
> - int fetch, blocking;
> + int fetch;
>
> - do
> - :: done != FINAL -> {
> - // Computing "blocking" is separate from execution of the
> - // "bottom half"
> - blocking = (req == 0);
> -
> - // This is our "bottom half"
> - atomic { fetch = req; req = 0; }
> - done = done | fetch;
> -
> - // Wait for a nudge from the other side
> - do
> - :: event == 1 -> { event = 0; break; }
> - :: !blocking -> break;
> - od;
> + do
> + :: true -> {
> + notify_me++;
>
> - dispatching = 1;
> + if
> +#ifndef BUG
> + :: (req > 0) -> skip;
> +#endif
> + :: else ->
> + // Wait for a nudge from the other side
> + do
> + :: event == 1 -> { event = 0; break; }
> + od;
> + fi;
>
> - // If you are simulating this model, you may want to add
> - // something like this here:
> - //
> - // int foo; foo++; foo++; foo++;
> - //
> - // This only wastes some time and makes it more likely
> - // that the notifier process hits the "fast path".
> + notify_me--;
>
> - dispatching = 0;
> + atomic { fetch = req; req = 0; }
> + done = done | fetch;
> }
> - :: else -> break;
> od
> }
>
> active proctype notifier()
> {
> int next = 1;
> - int sets = 0;
>
> do
> :: next <= LAST -> {
> @@ -74,8 +70,8 @@ active proctype notifier()
>
> // aio_notify
> if
> - :: dispatching == 0 -> sets++; event = 1;
> - :: else -> skip;
> + :: notify_me == 1 -> event = 1;
> + :: else -> printf("Skipped event_notifier_set\n");
> skip;
> fi;
>
> // Test both synchronous and asynchronous delivery
> @@ -86,19 +82,12 @@ active proctype notifier()
> :: 1 -> skip;
> fi;
> }
> - :: else -> break;
> od;
> - printf("Skipped %d event_notifier_set\n", MAX - sets);
> }
>
> -#define p (done == FINAL)
> -
> -never {
> - do
> - :: 1 // after an arbitrarily long prefix
> - :: p -> break // p becomes true
> - od;
> - do
> - :: !p -> accept: break // it then must remains true forever after
> - od
> +never { /* [] done < FINAL */
> +accept_init:
> + do
> + :: done < FINAL -> skip;
> + od;
> }
> diff --git a/include/block/aio.h b/include/block/aio.h
> index b46103e..be91e3f 100644
> --- a/include/block/aio.h
> +++ b/include/block/aio.h
> @@ -63,10 +63,30 @@ struct AioContext {
> */
> int walking_handlers;
>
> - /* Used to avoid unnecessary event_notifier_set calls in aio_notify.
> - * Writes protected by lock or BQL, reads are lockless.
> + /* Used to avoid unnecessary event_notifier_set calls in aio_notify;
> + * accessed with atomic primitives. If this field is 0, everything
> + * (file descriptors, bottom halves, timers) will be re-evaluated
> + * before the next blocking poll(), thus the event_notifier_set call
> + * can be skipped. If it is non-zero, you may need to wake up a
> + * concurrent aio_poll or the glib main event loop, making
> + * event_notifier_set necessary.
> + *
> + * Bit 0 is reserved for GSource usage of the AioContext, and is 1
> + * between a call to aio_ctx_check and the next call to aio_ctx_dispatch.
> + * Bits 1-31 simply count the number of active calls to aio_poll
> + * that are in the prepare or poll phase.
> + *
> + * The GSource and aio_poll must use a different mechanism because
> + * there is no certainty that a call to GSource's prepare callback
> + * (via g_main_context_prepare) is indeed followed by check and
> + * dispatch. It's not clear whether this would be a bug, but let's
> + * play safe and allow it---it will just cause extra calls to
> + * event_notifier_set until the next call to dispatch.
> + *
> + * Instead, the aio_poll calls include both the prepare and the
> + * dispatch phase, hence a simple counter is enough for them.
> */
> - bool dispatching;
> + uint32_t notify_me;
>
> /* lock to protect between bh's adders and deleter */
> QemuMutex bh_lock;
> @@ -89,9 +109,6 @@ struct AioContext {
> QEMUTimerListGroup tlg;
> };
>
> -/* Used internally to synchronize aio_poll against qemu_bh_schedule. */
> -void aio_set_dispatching(AioContext *ctx, bool dispatching);
> -
> /**
> * aio_context_new: Allocate a new AioContext.
> *
> diff --git a/tests/test-aio.c b/tests/test-aio.c
> index a7cb5c9..217e337 100644
> --- a/tests/test-aio.c
> +++ b/tests/test-aio.c
> @@ -97,14 +97,6 @@ static void event_ready_cb(EventNotifier *e)
>
> /* Tests using aio_*. */
>
> -static void test_notify(void)
> -{
> - g_assert(!aio_poll(ctx, false));
> - aio_notify(ctx);
> - g_assert(!aio_poll(ctx, true));
> - g_assert(!aio_poll(ctx, false));
> -}
> -
> typedef struct {
> QemuMutex start_lock;
> bool thread_acquired;
> @@ -331,7 +323,7 @@ static void test_wait_event_notifier(void)
> EventNotifierTestData data = { .n = 0, .active = 1 };
> event_notifier_init(&data.e, false);
> aio_set_event_notifier(ctx, &data.e, event_ready_cb);
> - g_assert(!aio_poll(ctx, false));
> + while (aio_poll(ctx, false));
> g_assert_cmpint(data.n, ==, 0);
> g_assert_cmpint(data.active, ==, 1);
>
> @@ -356,7 +348,7 @@ static void test_flush_event_notifier(void)
> EventNotifierTestData data = { .n = 0, .active = 10, .auto_set = true };
> event_notifier_init(&data.e, false);
> aio_set_event_notifier(ctx, &data.e, event_ready_cb);
> - g_assert(!aio_poll(ctx, false));
> + while (aio_poll(ctx, false));
> g_assert_cmpint(data.n, ==, 0);
> g_assert_cmpint(data.active, ==, 10);
>
> @@ -494,14 +486,6 @@ static void test_timer_schedule(void)
> * works well, and that's what I am using.
> */
>
> -static void test_source_notify(void)
> -{
> - while (g_main_context_iteration(NULL, false));
> - aio_notify(ctx);
> - g_assert(g_main_context_iteration(NULL, true));
> - g_assert(!g_main_context_iteration(NULL, false));
> -}
> -
> static void test_source_flush(void)
> {
> g_assert(!g_main_context_iteration(NULL, false));
> @@ -669,7 +653,7 @@ static void test_source_wait_event_notifier(void)
> EventNotifierTestData data = { .n = 0, .active = 1 };
> event_notifier_init(&data.e, false);
> aio_set_event_notifier(ctx, &data.e, event_ready_cb);
> - g_assert(g_main_context_iteration(NULL, false));
> + while (g_main_context_iteration(NULL, false));
> g_assert_cmpint(data.n, ==, 0);
> g_assert_cmpint(data.active, ==, 1);
>
> @@ -694,7 +678,7 @@ static void test_source_flush_event_notifier(void)
> EventNotifierTestData data = { .n = 0, .active = 10, .auto_set = true };
> event_notifier_init(&data.e, false);
> aio_set_event_notifier(ctx, &data.e, event_ready_cb);
> - g_assert(g_main_context_iteration(NULL, false));
> + while (g_main_context_iteration(NULL, false));
> g_assert_cmpint(data.n, ==, 0);
> g_assert_cmpint(data.active, ==, 10);
>
> @@ -830,7 +814,6 @@ int main(int argc, char **argv)
> while (g_main_context_iteration(NULL, false));
>
> g_test_init(&argc, &argv, NULL);
> - g_test_add_func("/aio/notify", test_notify);
> g_test_add_func("/aio/acquire", test_acquire);
> g_test_add_func("/aio/bh/schedule", test_bh_schedule);
> g_test_add_func("/aio/bh/schedule10", test_bh_schedule10);
> @@ -845,7 +828,6 @@ int main(int argc, char **argv)
> g_test_add_func("/aio/event/flush",
> test_flush_event_notifier);
> g_test_add_func("/aio/timer/schedule", test_timer_schedule);
>
> - g_test_add_func("/aio-gsource/notify",
> test_source_notify);
> g_test_add_func("/aio-gsource/flush",
> test_source_flush);
> g_test_add_func("/aio-gsource/bh/schedule",
> test_source_bh_schedule);
> g_test_add_func("/aio-gsource/bh/schedule10",
> test_source_bh_schedule10);
>