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Re: [Qemu-devel] [PATCH v2 2/6] monitor: accept chardev input from iothr
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] [PATCH v2 2/6] monitor: accept chardev input from iothread |
Date: |
Mon, 03 Dec 2018 08:10:37 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) |
Marc-André Lureau <address@hidden> writes:
> Chardev backends may not handle safely IO events from concurrent
> threads.
What exactly could go wrong? Or is this a well-known fact that doesn't
need further elaboration?
"safely handle I/O events"
> Better to wake up the chardev from the monitor IO thread if
> it's being used as the chardev context.
>
> Unify code paths by using a BH in all cases.
>
> Drop the now redundant aio_notify() call.
>
> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
> monitor.c | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/monitor.c b/monitor.c
> index 07712d89f9..511dd11d1c 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -4304,6 +4304,13 @@ int monitor_suspend(Monitor *mon)
> return 0;
> }
>
> +static void monitor_accept_input(void *opaque)
> +{
> + Monitor *mon = opaque;
> +
> + qemu_chr_fe_accept_input(&mon->chr);
> +}
> +
> void monitor_resume(Monitor *mon)
> {
> if (monitor_is_hmp_non_interactive(mon)) {
> @@ -4311,20 +4318,24 @@ void monitor_resume(Monitor *mon)
> }
>
> if (atomic_dec_fetch(&mon->suspend_cnt) == 0) {
> + AioContext *ctx = qemu_get_aio_context();
> +
> if (monitor_is_qmp(mon)) {
> /*
> * For QMP monitors that are running in the I/O thread,
> * let's kick the thread in case it's sleeping.
> */
> if (mon->use_io_thread) {
> - aio_notify(iothread_get_aio_context(mon_iothread));
> + ctx = iothread_get_aio_context(mon_iothread);
> }
> } else {
> assert(mon->rs);
> readline_show_prompt(mon->rs);
> }
Correct, since mon->use_io_thread can only be true in a QMP monitor so
far. But there's no need to depend on that here:
AioContext *ctx;
if (mon->use_io_thread) {
ctx = iothread_get_aio_context(mon_iothread);
} else {
ctx = qemu_get_aio_context();
}
if (!monitor_is_qmp(mon)) {
assert(mon->rs);
readline_show_prompt(mon->rs);
}
Same in monitor_suspend(), by the way.
The dependence in monitor_init() is tolerable, because it's the place
where the dependence is established.
> - qemu_chr_fe_accept_input(&mon->chr);
> +
> + aio_bh_schedule_oneshot(ctx, monitor_accept_input, mon);
> }
> +
> trace_monitor_suspend(mon, -1);
> }
- Re: [Qemu-devel] [PATCH v2 2/6] monitor: accept chardev input from iothread,
Markus Armbruster <=