Re: [Qemu-devel] [PATCH v6 5/7] qemu-coroutine-sleep: introduce qemu_co_sleep_wake

[Kevin Wolf <kwolf@redhat.com>]

Am 07.06.2019 um 13:18 hat Vladimir Sementsov-Ogievskiy geschrieben:
> 07.06.2019 10:57, Kevin Wolf wrote:
> > Am 11.04.2019 um 19:27 hat Vladimir Sementsov-Ogievskiy geschrieben:
> >> Introduce a function to gracefully wake-up a coroutine, sleeping in
> >> qemu_co_sleep_ns() sleep.
> >>
> >> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> > 
> > You can simply reenter the coroutine while it has yielded in
> > qemu_co_sleep_ns(). This is supported.
> 
> No it doesn't. qemu_aio_coroutine_enter checks for scheduled field,
> and aborts if it is set.

Ah, yes, it has been broken since commit

I actually tried to fix it once, but it turned out more complicated and
I think we found a different solution for the problem at hand:

    Subject: [PATCH for-2.11 0/4] Fix qemu-iotests failures
    Message-Id: <20171128154350.21504-1-kwolf@redhat.com>

In this case, I guess your approach with a new function to interrupt
qemu_co_sleep_ns() is okay.

Do we need to timer_del() when taking the shortcut? We don't necessarily
reenter the coroutine immediately, but might only be scheduling it. In
this case, the timer could fire before qemu_co_sleep_ns() has run and
schedule the coroutine a second time (ignoring co->scheduled again -
maybe we should actually not do that in the timer callback path, but
instead let it run into the assertion because it would be a bug for the
timer callback to end up in this situation).

Kevin