linux-kernel - Re: VirtIO console hangs

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Message-ID: <CAGnkfhy9okKAfZVkbO3YWPVmWgVm2LFzR-8=S73OfJ3bK_1FxQ@mail.gmail.com>
Date:   Fri, 31 Aug 2018 15:17:44 +0000
From:   Matteo Croce <mcroce@...hat.com>
To:     Nicholas Piggin <npiggin@...il.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, 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.

Cheers,
-- 
Matteo Croce
per aspera ad upstream