linux-kernel - [PATCH v1 1/2] driver core: Fix wait_for_device_probe() & deferred_probe

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Message-Id: <20220526034609.480766-2-saravanak@google.com>
Date:   Wed, 25 May 2022 20:46:08 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        John Stultz <john.stultz@...aro.org>,
        Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
        Saravana Kannan <saravanak@...gle.com>
Cc:     kernel-team@...roid.com, linux-kernel@...r.kernel.org,
        John Stultz <jstultz@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Robin Murphy <robin.murphy@....com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Basil Eljuse <Basil.Eljuse@....com>,
        Ferry Toth <fntoth@...il.com>, Arnd Bergmann <arnd@...db.de>,
        Anders Roxell <anders.roxell@...aro.org>,
        linux-pm@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH v1 1/2] driver core: Fix wait_for_device_probe() &
 deferred_probe_timeout interaction

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