[RFC][PATCH] driver core: Ensure wait_for_device_probe() waits until the deferred_probe_timeout fires

[John Stultz]

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" <davem@xxxxxxxxxxxxx>
Cc: Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>
Cc: Hideaki YOSHIFUJI <yoshfuji@xxxxxxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
Cc: Rob Herring <robh@xxxxxxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
Cc: netdev <netdev@xxxxxxxxxxxxxxx>
Cc: linux-pm@xxxxxxxxxxxxxxx
Reported-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
Fixes: c8c43cee29f6 ("driver core: Fix driver_deferred_probe_check_state() logic")
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
---
 drivers/base/dd.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 06ec0e851fa1..8c13f0df3282 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -232,9 +232,10 @@ DEFINE_SHOW_ATTRIBUTE(deferred_devs);
 int driver_deferred_probe_timeout = 30;
 #else
 /* In the case of !modules, no probe timeout needed */
-int driver_deferred_probe_timeout = -1;
+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)
 {
@@ -266,7 +267,7 @@ int driver_deferred_probe_check_state(struct device *dev)
 		return -ENODEV;
 	}
 
-	if (!driver_deferred_probe_timeout) {
+	if (!driver_deferred_probe_timeout && initcalls_done) {
 		dev_WARN(dev, "deferred probe timeout, ignoring dependency");
 		return -ETIMEDOUT;
 	}
@@ -284,6 +285,7 @@ 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);
 
@@ -658,6 +660,9 @@ 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);
 
-- 
2.17.1