Re: [PATCH] virtio: console: Don't block entire guest if host doesn't read data

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 10/19/2010 09:32 AM, Amit Shah wrote:
> On (Tue) Oct 19 2010 [09:23:00], Hans de Goede wrote:
>>>> 3) This patch will cause processes filling the virtqueue fast enough to block
>>>>     to never wake up again, due to a missing waitqueue wakeup, see:
>>>>     https://bugzilla.redhat.com/show_bug.cgi?id=643750
>>>
>>> Doesn't happen in my testcase, but this patch shouldn't cause that
>>> problem if it exists -- it's a problem that exists even now for
>>> nonblocking ports.  So if such a bug exists, it needs to be fixed
>>> independently.
>>
>> First of all lets agree that this is a real problem,
>
> Sure, got a testcase for the test-virtserial or kvm-autotest projects?
> ;-)
>
> I did try it and POLLOUT gets set for me immediately when I read one
> buffer from the host.
>

Ok, weird but ok :)

<snip>

>> I agree it is an independent problem, and should be fixed in a separate
>> patch, but that patch should be part of the same set and become *before*
>> this one, as this patch now extends the problem to ports opened in blocking
>> mode too.
>
> Strongly disagree.  This patch fixes a problem wherein blocking-mode
> writes to a port freeze the entire guest.  That's a much uglier problem
> to have than poll not indicating a port is writable again.

Ack, you're right.

Acked-by: Hans de Goede <hdegoede@redhat.com>

Regards,

Hans