driver core: Ensure wait_for_device_probe() waits until the deferred_probe_timeout fires

In commit c8c43ce ("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.

The downside to this solution is that kernel functionality that
uses wait_for_device_probe(), will block until the
driver_deferred_probe_timeout fires, regardless of if there is
any missing dependencies.

However, the previous patch reverts the default timeout value to
zero, so this side-effect will only affect users who specify a
driver_deferred_probe_timeout= value as a boot argument, where
the additional delay would be beneficial to allow modules to
load later during boot.

Thanks to Geert for chasing down that ip_auto_config was why NFS
was failing in this case!

Cc: "David S. Miller" <[email protected]>
Cc: Alexey Kuznetsov <[email protected]>
Cc: Hideaki YOSHIFUJI <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: Rob Herring <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Yoshihiro Shimoda <[email protected]>
Cc: Robin Murphy <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Sudeep Holla <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Naresh Kamboju <[email protected]>
Cc: Basil Eljuse <[email protected]>
Cc: Ferry Toth <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Anders Roxell <[email protected]>
Cc: [email protected]
Reported-by: Yoshihiro Shimoda <[email protected]>
Tested-by: Geert Uytterhoeven <[email protected]>
Tested-by: Yoshihiro Shimoda <[email protected]>
Fixes: c8c43ce ("driver core: Fix driver_deferred_probe_check_state() logic")
Signed-off-by: John Stultz <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: johnstultz-work

drivers/base/dd.c

@@ -226,6 +226,7 @@ DEFINE_SHOW_ATTRIBUTE(deferred_devs);
 
 int driver_deferred_probe_timeout;
 EXPORT_SYMBOL_GPL(driver_deferred_probe_timeout);
+static DECLARE_WAIT_QUEUE_HEAD(probe_timeout_waitqueue);
 
 static int __init deferred_probe_timeout_setup(char *str)
 {
@@ -275,6 +276,7 @@ static void deferred_probe_timeout_work_func(struct work_struct *work)
 
 	list_for_each_entry_safe(private, p, &deferred_probe_pending_list, deferred_probe)
 		dev_info(private->device, "deferred probe pending");
+	wake_up(&probe_timeout_waitqueue);
 }
 static DECLARE_DELAYED_WORK(deferred_probe_timeout_work, deferred_probe_timeout_work_func);
 
@@ -649,6 +651,9 @@ 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);