linux-kernel - Re: [PATCH v1] driver core: Extend deferred probe timeout on driver registration

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Message-ID: <Yo3WvGnNk3LvLb7R@linutronix.de>
Date:   Wed, 25 May 2022 09:11:56 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Rob Herring <robh@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Will Deacon <will@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Kevin Hilman <khilman@...nel.org>,
        Thierry Reding <treding@...dia.com>,
        Mark Brown <broonie@...nel.org>, Pavel Machek <pavel@....cz>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        linux-gpio@...r.kernel.org, linux-pm@...r.kernel.org,
        iommu@...ts.linux-foundation.org, kernel-team@...roid.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, John Stultz <jstultz@...gle.com>
Subject: Re: [PATCH v1] driver core: Extend deferred probe timeout on driver
 registration

On 2022-05-24 10:46:49 [-0700], Saravana Kannan wrote:
> > Removing probe_timeout_waitqueue (as suggested) or setting the timeout
> > to 0 avoids the delay.
> 
> In your case, I think it might be working as intended? Curious, what
> was the call stack in your case where it was blocked?

Why is then there 10sec delay during boot? The backtrace is
|------------[ cut here ]------------
|WARNING: CPU: 4 PID: 1 at drivers/base/dd.c:742 wait_for_device_probe+0x30/0x110
|Modules linked in:
|CPU: 4 PID: 1 Comm: swapper/0 Not tainted 5.18.0-rc5+ #154
|RIP: 0010:wait_for_device_probe+0x30/0x110
|Call Trace:
| <TASK>
| prepare_namespace+0x2b/0x160
| kernel_init_freeable+0x2b3/0x2dd
| kernel_init+0x11/0x110
| ret_from_fork+0x22/0x30
| </TASK>

Looking closer, it can't access init. This in particular box boots
directly the kernel without an initramfs so the kernel later mounts
/dev/sda1 and everything is good.  So that seems to be the reason…
My other machine with an initramfs does not show this problem.

> -Saravana

Sebastian