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Date:   Sat, 1 Sep 2018 08:57:25 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Matteo Croce <mcroce@...hat.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linux-kernel@...r.kernel.org,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Subject: Re: VirtIO console hangs

On Fri, 31 Aug 2018 15:17:44 +0000
Matteo Croce <mcroce@...hat.com> wrote:

> On Fri, Aug 31, 2018 at 3:49 AM Nicholas Piggin <npiggin@...il.com> wrote:
> >
> > On Tue, 28 Aug 2018 15:00:14 +0000
> > Matteo Croce <mcroce@...hat.com> wrote:
> >  
> > > On Tue, Aug 28, 2018 at 2:35 PM Nicholas Piggin <npiggin@...il.com> wrote:  
> > > >
> > > > On Tue, 28 Aug 2018 12:54:08 +0000
> > > > Matteo Croce <mcroce@...hat.com> wrote:
> > > >  
> > > > > With kernel 4.19.0-rc1 virtio_console hangs very often.
> > > > > I can always trigger the bug by pasting some characters in the
> > > > > terminal window, the console will stop receiving keypresses, but I can
> > > > > still see output from the console.
> > > > > Stangely, logging in the VM via SSH and sending lot of data to hvc0,
> > > > > like 'dmesg >/dev/hvc0' will fix the issue until the next paste.
> > > > >
> > > > > I did a git bisect and I've found that this is the offending commit,
> > > > > reverting it fixes it.
> > > > >
> > > > > Cheers,
> > > > >
> > > > > commit ec97eaad1383ab2500fcf9a07ade6044fbcc67f5
> > > > > Author: Nicholas Piggin <npiggin@...il.com>
> > > > > Date:   Tue May 1 00:55:54 2018 +1000
> > > > >
> > > > >     tty: hvc: hvc_poll() break hv read loop  
> > > >
> > > > Thanks for the report. I can't immediately see what the problem
> > > > is. Can you try get a stack trace of where it is stuck?
> > > >  
> > >
> > > I tried but didn't get one.
> > >  
> > > > Perhaps try this patch if you have time (it's a bit of a shot
> > > > in the dark).
> > > >  
> > >
> > > Yes it seems to fix. Thanks!  
> >
> > Okay sorry for the delay, I can reproduce it here and found a better
> > fix, if I could trouble you to test again.
> >
> > [PATCH] tty: hvc: hvc_poll() fix read loop hang
> >  
> 
> Hi Nicholas,
> 
> the patch works, but now pasting text inside the terminal is extremely
> slow, it feels worse than a 9600 baud serial line.
> 
> Btw, I had to apply the patch by hand as it was corrupted, some lines
> were collapsed into one.

Oh, when you revert the above commit, does it fix the speed problem as
well? I realise I'm testing with a remote machine that probably is not
connected with much better than 9600 baud... I will set up a local test.

Thanks,
Nick

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