linux-kernel - Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send

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Date:	Fri, 10 May 2013 17:42:13 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Borislav Petkov <bp@...en8.de>, Tony Luck <tony.luck@...el.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123
 native_smp_send_reschedule

On Fri, 10 May 2013, Frederic Weisbecker wrote:

> In fact it would be nice to have DO_ONCE(something) and stuff whatever
> we want inside.
> All the printk_once() et. al could even be implemented using that.

Sounds nice, but if it's going to be used for something else than purely 
debugging output, one has to keep in mind that printk_once() as currently 
implemented is actually racy.

I.e. you'd need to have locking (or at least cmpxchg) protecting the 
update of the static variable.

-- 
Jiri Kosina
SUSE Labs
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