linux-kernel - Re: [RFC][PATCH 3/4] ntp: Use printk

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Date:	Tue, 2 Jun 2015 12:43:16 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Jiri Bohac <jbohac@...e.cz>
cc:	John Stultz <john.stultz@...aro.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Prarit Bhargava <prarit@...hat.com>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	Jan Kara <jack@...e.cz>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [RFC][PATCH 3/4] ntp: Use printk_deferred in leapsecond path

On Tue, 2 Jun 2015, Jiri Bohac wrote:

> > Looking over the leapsecond code, I noticed the printk messages
> > reporting the leapsecond insertion in the second_overflow path
> > were not using the printk_deferred method. This was surprising
> > since the printk_deferred method was added in part to avoid
> > printk-ing while holding the timekeeping locks.
> > 
> > See 6d9bcb621b0b (timekeeping: use printk_deferred when holding
> > timekeeping seqlock) for further rational.
> > 
> > I can only guess that this omission was a git add -p oversight.
> 
> second_overflow() is called from accumulate_nsecs_to_secs().
> 
> accumulate_nsecs_to_secs() is called from update_wall_time()
> - once directly 
> - once via logarithmic_accumulation()
> Both calls are before write_seqcount_begin(&tk_core.seq).
> 
> So it looks safe to use printk there.

Couldn't we stuff a couple of

	!lockdep_is_held()

assertions into printk() so that we don't have to keep rediscovering this 
sort of problems over and over again?

Thanks,

-- 
Jiri Kosina
SUSE Labs

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