linux-kernel - Re: [RFC][PATCH] driver core: Ensure wait_for_device_probe() waits until the deferred_probe

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Date:   Tue, 7 Apr 2020 09:50:44 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Rob Herring <robh@...nel.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        netdev <netdev@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [RFC][PATCH] driver core: Ensure wait_for_device_probe() waits
 until the deferred_probe_timeout fires

Hi John,

On Tue, Apr 7, 2020 at 9:06 AM John Stultz <john.stultz@...aro.org> wrote:
> In commit c8c43cee29f6 ("driver core: Fix
> driver_deferred_probe_check_state() logic"), we set the default
> driver_deferred_probe_timeout value to 30 seconds to allow for
> drivers that are missing dependencies to have some time so that
> the dependency may be loaded from userland after initcalls_done
> is set.
>
> However, Yoshihiro Shimoda reported that on his device that
> expects to have unmet dependencies (due to "optional links" in
> its devicetree), was failing to mount the NFS root.
>
> In digging further, it seemed the problem was that while the
> device properly probes after waiting 30 seconds for any missing
> modules to load, the ip_auto_config() had already failed,
> resulting in NFS to fail. This was due to ip_auto_config()
> calling wait_for_device_probe() which doesn't wait for the
> driver_deferred_probe_timeout to fire.
>
> This patch tries to fix the issue by creating a waitqueue
> for the driver_deferred_probe_timeout, and calling wait_event()
> to make sure driver_deferred_probe_timeout is zero in
> wait_for_device_probe() to make sure all the probing is
> finished.
>
> NOTE: I'm not 100% sure this won't have other unwanted side
> effects (I don't have failing hardware myself to validate),
> so I'd apprecate testing and close review.
>
> If this approach doesn't work, I'll simply set the default
> driver_deferred_probe_timeout value back to zero, to avoid any
> behavioral change from before.
>
> Thanks to Geert for chasing down that ip_auto_config was why NFS
> was failing in this case!
>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Alexey Kuznetsov <kuznet@....inr.ac.ru>
> Cc: Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Rafael J. Wysocki <rjw@...ysocki.net>
> Cc: Rob Herring <robh@...nel.org>
> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
> Cc: netdev <netdev@...r.kernel.org>
> Cc: linux-pm@...r.kernel.org
> Reported-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
> Fixes: c8c43cee29f6 ("driver core: Fix driver_deferred_probe_check_state() logic")
> Signed-off-by: John Stultz <john.stultz@...aro.org>

Thanks, this fixes the issue for me!

Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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