linux-kernel - Re: Revert "leds: avoid races with workqueue"?

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Date:   Sun, 26 May 2019 19:20:02 +0200
From:   Pavel Machek <pavel@....cz>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Revert "leds: avoid races with workqueue"?

On Sat 2019-05-25 10:32:31, Hugh Dickins wrote:
> On Sat, 25 May 2019, Pavel Machek wrote:
> 
> > Hi!
> > 
> > > I'm having to revert 0db37915d912 ("leds: avoid races with workqueue")
> > > from my 5.2-rc testing tree, because lockdep and other debug options
> > > don't like it: net/mac80211/led.c arranges for led_blink_setup() to be
> > > called at softirq time, and flush_work() is not good for calling
> > > then.
> > 
> > This should keep X60 working (as well as it is now; X60 will still
> > have problems with lost events in setup like yours).
> > 
> > Can you test this instead of the revert?
> 
> Thanks, Pavel: yes, that works fine for me on the T420s, no debug
> complaints, good and silent; and the wifi LED is blinking as before.

I'd like to prevent recurrence of similar problem, and I wonder if you
can give me a hint.

I can annotate code that can sleep with might_sleep().

How can I annotate code that can not sleep? I might do 

spin_lock(&dummy);
this_should_not_sleep();
spin_unlock(&dummy);

But I don't really need extra serialization. I just want annotations for
lockdep. Any ideas?

								Pavel