Re: [Qemu-devel] [Qemu-block] [PATCH] qed: fix bdrv_qed_drain

[Kevin Wolf <kwolf@redhat.com>]

Am 23.02.2016 um 14:54 hat Paolo Bonzini geschrieben:
> 
> 
> On 23/02/2016 13:49, Fam Zheng wrote:
> > On Tue, 02/23 11:43, Paolo Bonzini wrote:
> >>
> >>
> >> On 23/02/2016 06:57, Fam Zheng wrote:
> >>>>>> +        qed_cancel_need_check_timer(s);
> >>>>>> +        qed_need_check_timer_cb(s);
> >>>>>> +    }
> >>>>>
> >>>>> What if an allocating write is queued (the else branch case)? Its completion
> >>>>> will be in bdrv_drain and it could arm the need_check_timer which is wrong.
> >>>>>
> >>>>> We need to drain the allocating_write_reqs queue before checking the timer.
> >>>>
> >>>> You're right, but how?  That's what bdrv_drain(bs) does, it's a
> >>>> chicken-and-egg problem.
> >>>
> >>> Maybe use an aio_poll loop before the if?
> >>
> >> That would not change the fact that you're reimplementing bdrv_drain
> >> inside bdrv_qed_drain.
> > 
> > But it fulfills the contract of .bdrv_drain. This is the easy way, the hard way
> > would be iterating through the allocating_write_reqs list and process reqs one
> > by one synchronously, which still involves aio_poll indirectly.
> 
> The easy way would be better then.
> 
> Stefan, any second opinion?

What's the status here? It would be good to have qed not segfaulting all
the time.

Kevin