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

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Message-ID: <20150602103144.GB18714@midget.suse.cz>
Date:	Tue, 2 Jun 2015 12:31:44 +0200
From:	Jiri Bohac <jbohac@...e.cz>
To:	John Stultz <john.stultz@...aro.org>
Cc:	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

Hi,

On Fri, May 29, 2015 at 01:24:27PM -0700, John Stultz 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.

Regards,

-- 
Jiri Bohac <jbohac@...e.cz>
SUSE Labs, SUSE CZ

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