[PATCH v1 0/2] Fix issues with deferred_probe_timeout being non-zero

[PATCH v1 0/2] Fix issues with deferred_probe_timeout being non-zero

[Saravana Kannan]

Setting deferred_probe_timeout to a non-zero default used to cause
issues with NFS rootfs. But the fix for that is causing other problem.
So revert the fix and set the default deferred_probe_timeout back to
zero.

Most of the Cc list if from commit 35a672363ab3. Please let me know if
you want to be removed from future patches related to
deferred_probe_timeout and NFS rootfs issues.

-Saravana

Saravana Kannan (2):
  driver core: Fix wait_for_device_probe() & deferred_probe_timeout
    interaction
  driver core: Set default deferred_probe_timeout back to 0.

 drivers/base/dd.c | 10 ----------
 1 file changed, 10 deletions(-)

-- 
2.36.1.124.g0e6072fb45-goog

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

[Saravana Kannan]

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@google.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Rob Herring <robh@kernel.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>
Cc: Basil Eljuse <Basil.Eljuse@arm.com>
Cc: Ferry Toth <fntoth@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Anders Roxell <anders.roxell@linaro.org>
Cc: linux-pm@vger.kernel.org
Fixes: 35a672363ab3 ("driver core: Ensure wait_for_device_probe() waits until the deferred_probe_timeout fires")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Saravana Kannan <saravanak@google.com>
---

 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);
 
-- 
2.36.1.124.g0e6072fb45-goog

[PATCH v1 2/2] driver core: Set default deferred_probe_timeout back to 0.

[Saravana Kannan]

Since we had to effectively reverted
commit 35a672363ab3 ("driver core: Ensure wait_for_device_probe() waits
until the deferred_probe_timeout fires") in an earlier patch, a non-zero
deferred_probe_timeout will break NFS rootfs mounting [1] again. So, set
the default back to zero until we can fix that.

[1] - https://lore.kernel.org/lkml/TYAPR01MB45443DF63B9EF29054F7C41FD8C60@TYAPR01MB4544.jpnprd01.prod.outlook.com/

Cc: Mark Brown <broonie@kernel.org>
Cc: Rob Herring <robh@kernel.org>
Reported-by: Nathan Chancellor <nathan@kernel.org>
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Fixes: 2b28a1a84a0e ("driver core: Extend deferred probe timeout on driver registration")
Signed-off-by: Saravana Kannan <saravanak@google.com>
---
 drivers/base/dd.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 91f63cd33b12..251b5ba1b84a 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -256,12 +256,7 @@ static int deferred_devs_show(struct seq_file *s, void *data)
 }
 DEFINE_SHOW_ATTRIBUTE(deferred_devs);
 
-#ifdef CONFIG_MODULES
-int driver_deferred_probe_timeout = 10;
-#else
 int driver_deferred_probe_timeout;
-#endif
-
 EXPORT_SYMBOL_GPL(driver_deferred_probe_timeout);
 
 static int __init deferred_probe_timeout_setup(char *str)
-- 
2.36.1.124.g0e6072fb45-goog

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@google.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@google.com>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
> Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Geert Uytterhoeven <geert@linux-m68k.org>
> Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
> Cc: Sudeep Holla <sudeep.holla@arm.com>
> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Cc: Naresh Kamboju <naresh.kamboju@linaro.org>
> Cc: Basil Eljuse <Basil.Eljuse@arm.com>
> Cc: Ferry Toth <fntoth@gmail.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Anders Roxell <anders.roxell@linaro.org>
> Cc: linux-pm@vger.kernel.org
> Fixes: 35a672363ab3 ("driver core: Ensure wait_for_device_probe() waits until the deferred_probe_timeout fires")
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Saravana Kannan <saravanak@google.com>

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

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

thanks
-john

Re: [PATCH v1 0/2] Fix issues with deferred_probe_timeout being non-zero

[Geert Uytterhoeven]

Hi Saravana,

On Thu, May 26, 2022 at 10:22 AM Saravana Kannan <saravanak@google.com> wrote:
> Setting deferred_probe_timeout to a non-zero default used to cause
> issues with NFS rootfs. But the fix for that is causing other problem.
> So revert the fix and set the default deferred_probe_timeout back to
> zero.
>
> Most of the Cc list if from commit 35a672363ab3. Please let me know if
> you want to be removed from future patches related to
> deferred_probe_timeout and NFS rootfs issues.

Thanks for your series!

On Salvator-XS, Micrel KSZ9031 Gigabit PHY probe is no longer delayed
by 9s after applying this series.
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

Gr{oetje,eeting}s,

                        Geert

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