From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hans de Goede Subject: Re: [PATCH] virtio: console: Don't block entire guest if host doesn't read data Date: Tue, 19 Oct 2010 10:03:48 +0200 Message-ID: <4CBD50E4.7090308@redhat.com> References: <4CBD40D4.9050106@redhat.com> <20101019071021.GB2505@amit-laptop.redhat.com> <4CBD4754.5030504@redhat.com> <20101019073216.GA8896@amit-laptop.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20101019073216.GA8896@amit-laptop.redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Amit Shah Cc: stable@kernel.org, Virtualization List List-Id: virtualization@lists.linuxfoundation.org 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 :) >> 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 Regards, Hans