linux-kernel - Re: [PATCH v1 1/2] driver core: Fix wait_for_device_probe() & deferred_probe

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Date:   Wed, 25 May 2022 21:04:55 -0700
From:   John Stultz <jstultz@...gle.com>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        John Stultz <john.stultz@...aro.org>,
        Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
        kernel-team@...roid.com, 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>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Robin Murphy <robin.murphy@....com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Basil Eljuse <Basil.Eljuse@....com>,
        Ferry Toth <fntoth@...il.com>, Arnd Bergmann <arnd@...db.de>,
        Anders Roxell <anders.roxell@...aro.org>,
        linux-pm@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH v1 1/2] driver core: Fix wait_for_device_probe() &
 deferred_probe_timeout interaction

On Wed, May 25, 2022 at 8:46 PM Saravana Kannan <saravanak@...gle.com> wrote:
>
> 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/
>
> Cc: John Stultz <jstultz@...gle.com>
> 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: 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: Robin Murphy <robin.murphy@....com>
> Cc: Andy Shevchenko <andy.shevchenko@...il.com>
> Cc: Sudeep Holla <sudeep.holla@....com>
> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Cc: Naresh Kamboju <naresh.kamboju@...aro.org>
> Cc: Basil Eljuse <Basil.Eljuse@....com>
> Cc: Ferry Toth <fntoth@...il.com>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Anders Roxell <anders.roxell@...aro.org>
> Cc: linux-pm@...r.kernel.org
> Fixes: 35a672363ab3 ("driver core: Ensure wait_for_device_probe() waits until the deferred_probe_timeout fires")
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Reported-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Signed-off-by: Saravana Kannan <saravanak@...gle.com>

Apologies for the trouble this caused. Thanks for chasing it down!

Acked-by: John Stultz <jstultz@...gle.com>

thanks
-john