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main-loop: fix qemu_notify_event for aio_notify optimization

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aio_notify can be optimized away, and in fact almost always will.  However,
qemu_notify_event is used in places where this is incorrect---most notably,
when handling SIGTERM.  When aio_notify is optimized away, it is possible that
QEMU enters a blocking ppoll immediately afterwards and stays there, without
reaching main_loop_should_exit().

Fix this by using a bottom half.  The bottom half can be optimized too, but
scheduling it is enough for the ppoll not to block.  The hang is thus avoided.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1437738175-23624-1-git-send-email-pbonzini@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Paolo Bonzini 2015-07-24 13:42:55 +02:00 committed by Peter Maydell
parent 3737129917
commit edec47cfef
1 changed files with 10 additions and 1 deletions
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11
main-loop.c
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@ -114,6 +114,14 @@ static int qemu_signal_init(void)
#endif
static AioContext *qemu_aio_context;
static QEMUBH *qemu_notify_bh;
static void notify_event_cb(void *opaque)
{
/* No need to do anything; this bottom half is only used to
* kick the kernel out of ppoll/poll/WaitForMultipleObjects.
*/
}
AioContext *qemu_get_aio_context(void)
{
@ -125,7 +133,7 @@ void qemu_notify_event(void)
if (!qemu_aio_context) {
return;
}
aio_notify(qemu_aio_context);
qemu_bh_schedule(qemu_notify_bh);
}
static GArray *gpollfds;
@ -144,6 +152,7 @@ int qemu_init_main_loop(Error **errp)
}
qemu_aio_context = aio_context_new(&local_error);
qemu_notify_bh = qemu_bh_new(notify_event_cb, NULL);
if (!qemu_aio_context) {
error_propagate(errp, local_error);
return -EMFILE;