linux-kernel - Re: VirtIO console hangs

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Date:   Wed, 29 Aug 2018 01:33:36 +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
Subject: Re: VirtIO console hangs

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!

Great thanks for testing it so quickly.

I would have thought the return code should cause another poll to
trigger. I'll have to read the code again and try to find out what
I missed.

Thanks,
Nick