Re: [PATCH v2 14/18] util/timer: avoid deadlock when shutting down

[Pierrick Bouvier <pierrick.bouvier@linaro.org>]

On 9/16/24 01:53, Alex Bennée wrote:
> When we shut down a guest we disable the timers. However this can
> cause deadlock if the guest has queued some async work that is trying
> to advance system time and spins forever trying to wind time forward.
> Pay attention to the return code and bail early if we can't wind time
> forward.
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> Reported-by: Elisha Hollander <just4now666666@gmail.com>
> ---
>   util/qemu-timer.c | 14 ++++++++++++--
>   1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/util/qemu-timer.c b/util/qemu-timer.c
> index 213114be68..6b1533bc2a 100644
> --- a/util/qemu-timer.c
> +++ b/util/qemu-timer.c
> @@ -685,10 +685,17 @@ int64_t qemu_clock_advance_virtual_time(int64_t dest)
>   {
>       int64_t clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
>       AioContext *aio_context;
> +    int64_t deadline;
> +
>       aio_context = qemu_get_aio_context();
> -    while (clock < dest) {
> -        int64_t deadline = qemu_clock_deadline_ns_all(QEMU_CLOCK_VIRTUAL,
> +
> +    deadline = qemu_clock_deadline_ns_all(QEMU_CLOCK_VIRTUAL,
>                                                         QEMU_TIMER_ATTR_ALL);
> +    /*
> +     * A deadline of < 0 indicates this timer is not enabled, so we
> +     * won't get far trying to run it forward.
> +     */
> +    while (deadline >= 0 && clock < dest) {
>           int64_t warp = qemu_soonest_timeout(dest - clock, deadline);
>   
>           qemu_virtual_clock_set_ns(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + warp);
> @@ -696,6 +703,9 @@ int64_t qemu_clock_advance_virtual_time(int64_t dest)
>           qemu_clock_run_timers(QEMU_CLOCK_VIRTUAL);
>           timerlist_run_timers(aio_context->tlg.tl[QEMU_CLOCK_VIRTUAL]);
>           clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
> +
> +        deadline = qemu_clock_deadline_ns_all(QEMU_CLOCK_VIRTUAL,
> +                                              QEMU_TIMER_ATTR_ALL);
>       }
>       qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
>   

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>