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SubjectRe: [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 <> 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" <>
> Cc: Alexey Kuznetsov <>
> Cc: Hideaki YOSHIFUJI <>
> Cc: Jakub Kicinski <>
> Cc: Greg Kroah-Hartman <>
> Cc: Rafael J. Wysocki <>
> Cc: Rob Herring <>
> Cc: Geert Uytterhoeven <>
> Cc: Yoshihiro Shimoda <>
> Cc: netdev <>
> Cc:
> Reported-by: Yoshihiro Shimoda <>
> Fixes: c8c43cee29f6 ("driver core: Fix driver_deferred_probe_check_state() logic")
> Signed-off-by: John Stultz <>

Thanks, this fixes the issue for me!

Tested-by: Geert Uytterhoeven <>



Geert Uytterhoeven -- There's lots of Linux beyond ia32 --

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

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