linux-kernel - Re: is printk() safe within a timekeeper

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Date:	Wed, 12 Mar 2014 10:21:25 +0100
From:	Jiri Bohac <jbohac@...e.cz>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Jiri Bohac <jbohac@...e.cz>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: is printk() safe within a timekeeper_seq write section?

On Tue, Mar 11, 2014 at 02:54:13PM -0700, John Stultz wrote:
> Ok, so a generic solution is probably not going to be worth it then. My
> thought was that since we do a very limited amount of informational
> printks in the timekeeping code, we can be fairly safe delaying the
> print-out until we drop the locks.
> 
> For timekeeping, its really 4 call sites:
> * invalid inject_sleep_time deltas
> * > 11% clocksource freq adjustments
> * insert leap second
> * delete leap second

I believe these last two were made safe by 
commit ca4523cd (timekeeping: Shorten seq_count region). 

write_seqcount_begin(&timekeeper_seq) is now done after the
accumulate_nsecs_to_secs(tk) from where the printks are called.

Regards,

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

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