Re: [PATCH v1 1/2] driver core: Fix wait_for_device_probe() & deferred_probe_timeout interaction

[John Stultz]

On Wed, May 25, 2022 at 8:46 PM Saravana Kannan <saravanak@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> [2] - https://lore.kernel.org/lkml/YowHNo4sBjr9ijZr@dev-arch.thelio-3990X/
> [3] - https://lore.kernel.org/lkml/Yo3WvGnNk3LvLb7R@xxxxxxxxxxxxx/
>
> Cc: John Stultz <jstultz@xxxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>
> Cc: Hideaki YOSHIFUJI <yoshfuji@xxxxxxxxxxxxxx>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> Cc: Rob Herring <robh@xxxxxxxxxx>
> Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
> Cc: Robin Murphy <robin.murphy@xxxxxxx>
> Cc: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
> Cc: Sudeep Holla <sudeep.holla@xxxxxxx>
> Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Cc: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
> Cc: Basil Eljuse <Basil.Eljuse@xxxxxxx>
> Cc: Ferry Toth <fntoth@xxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Anders Roxell <anders.roxell@xxxxxxxxxx>
> Cc: linux-pm@xxxxxxxxxxxxxxx
> Fixes: 35a672363ab3 ("driver core: Ensure wait_for_device_probe() waits until the deferred_probe_timeout fires")
> Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Reported-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Signed-off-by: Saravana Kannan <saravanak@xxxxxxxxxx>

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

Acked-by: John Stultz <jstultz@xxxxxxxxxx>

thanks
-john