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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Wed, 16 Aug 2023 12:10:53 +0200
Message-ID: <CAMuHMdVrWotHv5qTW0j_=uZsmwv7Vrkg-rm-=U=YbffsSfwfCg@mail.gmail.com>
Subject: Re: [PATCH 5.17 127/298] driver core: Fix wait_for_device_probe() &
 deferred_probe_timeout interaction
To:     Shreeya Patel <shreeya.patel@collabora.com>
Cc:     saravanak@google.com,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, John Stultz <jstultz@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Rob Herring <robh@kernel.org>,
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Hi Shreeya,

On Wed, Aug 16, 2023 at 11:39 AM Shreeya Patel
<shreeya.patel@collabora.com> wrote:
> On 13/06/22 15:40, Greg Kroah-Hartman wrote:
> > From: Saravana Kannan<saravanak@google.com>
> >
> > [ Upstream commit 5ee76c256e928455212ab759c51d198fedbe7523 ]
> >
> > Mounting NFS rootfs was timing out when deferred_probe_timeout was
> > non-zero [1].  This was because ip_auto_config() initcall times out
> > waiting for the network interfaces to show up when
> > deferred_probe_timeout was non-zero. While ip_auto_config() calls
> > wait_for_device_probe() to make sure any currently running deferred
> > probe work or asynchronous probe finishes, that wasn't sufficient to
> > account for devices being deferred until deferred_probe_timeout.
> >
> > Commit 35a672363ab3 ("driver core: Ensure wait_for_device_probe() waits
> > until the deferred_probe_timeout fires") tried to fix that by making
> > sure wait_for_device_probe() waits for deferred_probe_timeout to expire
> > before returning.
> >
> > However, if wait_for_device_probe() is called from the kernel_init()
> > context:
> >
> > - Before deferred_probe_initcall() [2], it causes the boot process to
> >    hang due to a deadlock.
> >
> > - After deferred_probe_initcall() [3], it blocks kernel_init() from
> >    continuing till deferred_probe_timeout expires and beats the point of
> >    deferred_probe_timeout that's trying to wait for userspace to load
> >    modules.
> >
> > Neither of this is good. So revert the changes to
> > wait_for_device_probe().
> >
> > [1] -https://lore.kernel.org/lkml/TYAPR01MB45443DF63B9EF29054F7C41FD8C60@TYAPR01MB4544.jpnprd01.prod.outlook.com/
> > [2] -https://lore.kernel.org/lkml/YowHNo4sBjr9ijZr@dev-arch.thelio-3990X/
> > [3] -https://lore.kernel.org/lkml/Yo3WvGnNk3LvLb7R@linutronix.de/
>
> Hi Saravana, Greg,
>
>
> KernelCI found this patch causes the baseline.bootrr.deferred-probe-empty test to fail on r8a77960-ulcb,
> see the following details for more information.

Commit 9be4cbd09da820a2 ("driver core: Set default deferred_probe_timeout
back to 0.") in v5.19 contains a reference to the same commit as
mentioned in the Fixes tag.  Does backporting that help?

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