Re: Regression with a0747a859ef6 ("bdi: add error handle for bdi_debug_register")

From: James Bottomley
Date: Thu Dec 21 2017 - 19:29:39 EST

On Thu, 2017-12-21 at 10:02 -0700, Jens Axboe wrote:
> On 12/21/17 9:42 AM, Bruno Wolff III wrote:
> >
> > On Thu, Dec 21, 2017 at 23:48:19 +0800,
> > Â weiping zhang <zwp10758@xxxxxxxxx> wrote:
> > >
> > > >
> > > > output you want. I never saw it for any kernels I compiled
> > > > myself. Only when I test kernels built by Fedora do I see it.
> > > > see it every boot ?
> >
> > I don't look every boot. The warning gets scrolled of the screen.
> > Once I see the CPU hang warnings I know the boot is failing. I
> > don't always look at journalctl later to see what's there.
> I'm going to revert a0747a859ef6 for now, since we're now 8 days into
> this and no progress has been made on fixing it.

I think this is correct. ÂIf you build the kernel with
CONFIG_DEBUG_FS=N, you're definitely going to get the same hang
(because the debugfs_ functions fail with -ENODEV and the bdi will
never get registered). ÂThis alone leads me to suspect the commit is
bogus because it's a randconfig/test accident waiting to happen.

We should still root cause the debugfs failure in this case, but I
really think debugfs files should be treated as optional, so a failure
in setting them up should translate to some sort of warning not a
failure to set up the bdi.