Re: [PATCH v2 6/9] Revert "driver core: Set default deferred_probe_timeout back to 0."

Geert Uytterhoeven
2022-07-21T08:40:48Z

Hi Saravana,

On Wed, Jul 20, 2022 at 9:02 PM Saravana Kannan <saravanak@google.com> wrote:
> On Wed, Jul 20, 2022 at 10:31 AM Geert Uytterhoeven
> <geert@linux-m68k.org> wrote:
> > On Wed, Jun 1, 2022 at 9:45 AM Saravana Kannan <saravanak@google.com> wrote:
> > > This reverts commit 11f7e7ef553b6b93ac1aa74a3c2011b9cc8aeb61.
> > >
> > > Let's take another shot at getting deferred_probe_timeout=10 to work.
> > >
> > > Signed-off-by: Saravana Kannan <saravanak@google.com>
> >
> > Thanks for your patch, which is now commit f516d01b9df2782b
> > ("Revert "driver core: Set default deferred_probe_timeout
> > back to 0."") in driver-core/driver-core-next.
> >
> > Wolfram found an issue on a Renesas board where disabling the IOMMU
> > driver (CONFIG_IPMMU_VMSA=n) causes the system to fail to boot,
> > and bisected this to a merge of driver-core/driver-core-next.
> > After some trials, I managed to reproduce the issue, and bisected it
> > further to commit f516d01b9df2782b.
> >
> > The affected config has:
> > CONFIG_MODULES=y
> > CONFIG_RCAR_DMAC=y
> > CONFIG_IPMMU_VMSA=n
> >
> > In arch/arm64/boot/dts/renesas/r8a77951-salvator-xs.dtb,
> > e6e88000.serial links to a dmac, and the dmac links to an iommu,
> > for which no driver is available.
>
> Thanks for digging into this and giving more details.
>
> Is e6e88000.serial being blocked the reason for the boot failure?

It doesn't seem to be.

> If so, can you give this a shot?
> https://lore.kernel.org/lkml/20220701012647.2007122-1-saravanak@google.com/

Thanks, but it doesn't make a difference.

> > After bisecting configs, I found the culprit: CONFIG_IP_PNP.
> > As Wolfram was using an initramfs, CONFIG_IP_PNP was not needed.
> > If CONFIG_IP_PNP=n, booting fails.
> > If CONFIG_IP_PNP=y, booting succeeds.
> > In fact, just disabling late_initcall(ip_auto_config) makes it fail,
> > too.
> > Reducing ip_auto_config(), it turns out the call to
> > wait_for_init_devices_probe() is what is needed to unblock booting.
> >
> > So I guess wait_for_init_devices_probe() needs to be called (where?)
> > if CONFIG_IP_PNP=n, too?
>
> That function just unblocks all devices and allows them to try and
> probe and then waits for all possible probes to finish before
> returning. They problem with call it randomly/every time is that it
> breaks functionality where an optional supplier will probe after a few
> modules are loaded in the future.
>
> I guess one possible issue with the timeout not helping is that once
> the timeout expires, things are still being probed and nothing is
> being blocked till they finish probing.

I'm not sure that it's a device that's missing.

Calling wait_for_init_devices_probe() or not changes lots of little
things in the probing order. But when comparing the sorted boot logs,
there does not seem to be any difference in the list of devices that
was probed successfully.
It looks like the system is just blocked on something else?...

I tried getting a list of all locks held using Magic SysRq + d,
but Magic SysRq on the serial console does not work at this point
(it does work in the booted kernel with CONFIG_IP_PNP=y).

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds