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

[Rafael J. Wysocki]

On Fri, Jun 3, 2022 at 1:32 PM Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> From: Saravana Kannan <saravanak@xxxxxxxxxx>
>
> 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/
>
> Fixes: 35a672363ab3 ("driver core: Ensure wait_for_device_probe() waits until the deferred_probe_timeout fires")
> 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
> Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Reported-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Tested-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> Acked-by: John Stultz <jstultz@xxxxxxxxxx>
> Signed-off-by: Saravana Kannan <saravanak@xxxxxxxxxx>
> Link: https://lore.kernel.org/r/20220526034609.480766-2-saravanak@xxxxxxxxxx
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

Reviewed-by: Rafael J. Wysocki <rafael@xxxxxxxxxx>

> ---
>  drivers/base/dd.c | 5 -----
>  1 file changed, 5 deletions(-)
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 2fc8507f59ee..91f63cd33b12 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -263,7 +263,6 @@ int driver_deferred_probe_timeout;
>  #endif
>
>  EXPORT_SYMBOL_GPL(driver_deferred_probe_timeout);
> -static DECLARE_WAIT_QUEUE_HEAD(probe_timeout_waitqueue);
>
>  static int __init deferred_probe_timeout_setup(char *str)
>  {
> @@ -318,7 +317,6 @@ static void deferred_probe_timeout_work_func(struct work_struct *work)
>         list_for_each_entry(p, &deferred_probe_pending_list, deferred_probe)
>                 dev_info(p->device, "deferred probe pending\n");
>         mutex_unlock(&deferred_probe_mutex);
> -       wake_up_all(&probe_timeout_waitqueue);
>  }
>  static DECLARE_DELAYED_WORK(deferred_probe_timeout_work, deferred_probe_timeout_work_func);
>
> @@ -736,9 +734,6 @@ int driver_probe_done(void)
>   */
>  void wait_for_device_probe(void)
>  {
> -       /* wait for probe timeout */
> -       wait_event(probe_timeout_waitqueue, !driver_deferred_probe_timeout);
> -
>         /* wait for the deferred probe workqueue to finish */
>         flush_work(&deferred_probe_work);
>
> --
> 2.36.1
>