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    Subject[PATCH 1/2] driver core: Fix wait_for_device_probe() & deferred_probe_timeout interaction
    Date
    From: Saravana Kannan <saravanak@google.com>

    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/

    Fixes: 35a672363ab3 ("driver core: Ensure wait_for_device_probe() waits until the deferred_probe_timeout fires")
    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
    Reported-by: Nathan Chancellor <nathan@kernel.org>
    Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
    Acked-by: John Stultz <jstultz@google.com>
    Signed-off-by: Saravana Kannan <saravanak@google.com>
    Link: https://lore.kernel.org/r/20220526034609.480766-2-saravanak@google.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    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
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