netdev - [RESEND] Re: usb/net/p54: trying to register non-static key in p54_unregister

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Date:   Sat, 23 Sep 2017 21:37:34 +0200
From:   Christian Lamparter <chunkeey@...glemail.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Johannes Berg <johannes@...solutions.net>,
        Kalle Valo <kvalo@...eaurora.org>,
        linux-wireless@...r.kernel.org, netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>,
        Stephen Boyd <sboyd@...eaurora.org>, Tejun Heo <tj@...nel.org>,
        Yong Zhang <yong.zhang0@...il.com>
Subject: [RESEND] Re: usb/net/p54: trying to register non-static key in p54_unregister_leds

This got rejected by gmail once. Let's see if it works now.

On Thursday, September 21, 2017 8:22:45 PM CEST Andrey Konovalov wrote:
> On Wed, Sep 20, 2017 at 9:55 PM, Johannes Berg
> <johannes@...solutions.net> wrote:
> > On Wed, 2017-09-20 at 21:27 +0200, Christian Lamparter wrote:
> >
> >> It seems this is caused as a result of:
> >>     -> lock_map_acquire(&work->lockdep_map);
> >>           lock_map_release(&work->lockdep_map);
> >>
> >>     in flush_work() [0]
> >
> > Agree.
> >
> >> This was added by:
> >>
> >>       commit 0976dfc1d0cd80a4e9dfaf87bd8744612bde475a
> >>       Author: Stephen Boyd <sboyd@...eaurora.org>
> >>       Date:   Fri Apr 20 17:28:50 2012 -0700
> >>
> >>       workqueue: Catch more locking problems with flush_work()
> >
> > Yes, but that doesn't matter.
> >
> >> Looking at the Stephen's patch, it's clear that it was made
> >> with "static DECLARE_WORK(work, my_work)" in mind. However
> >> p54's led_work is "per-device", hence it is stored in the
> >> devices context p54_common, which is dynamically allocated.
> >> So, maybe revert Stephen's patch?
> >
> > I disagree - as the lockdep warning says:
> >
> >> > INFO: trying to register non-static key.
> >> > the code is fine but needs lockdep annotation.
> >> > turning off the locking correctness validator.
> >
> > What it needs is to actually correctly go through initializing the work
> > at least once.
> >
> > Without more information, I can't really say what's going on, but I
> > assume that something is failing and p54_unregister_leds() is getting
> > invoked without p54_init_leds() having been invoked, so essentially
> > it's trying to flush a work that was never initialized?
> >
> > INIT_DELAYED_WORK() does, after all, initialize the lockdep map
> > properly via __INIT_WORK().

Ok, thanks. This does indeed explain it.

But this also begs the question: Is this really working then?
>From what I can tell, if CONFIG_LOCKDEP is not set then there's no BUG
no WARN, no other splat or any other odd system behaviour. Does
[cancel | flush]_[delayed_]work[_sync] really "just work" by *accident*,
as long the delayed_work | work_struct is zeroed out? 
And should it work in the future as well?

> Since I'm able to reproduce this, please let me know if you need me to
> collect some debug traces to help with the triage.

Do you want to take a shot at making a patch too? At a quick glance, it
should be enough to move the [#ifdef CONFIG_P54_LEDS ... #endif] block
in p54_unregister_common() into the if (priv->registered) { block
(preferably before the ieee80211_unregister_hw(dev).

Regards,
Christian