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Subject: Re: [PATCH] Fix CPU spinlock lockups on secondary CPU bringup
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-omap@vger.kernel.org
In-Reply-To: <20110622105550.GQ23234@n2100.arm.linux.org.uk>
References: <20110622105550.GQ23234@n2100.arm.linux.org.uk>
Content-Type: text/plain; charset="UTF-8"
Date: Wed, 22 Jun 2011 20:46:48 +0200
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Le mercredi 22 juin 2011 à 11:55 +0100, Russell King - ARM Linux a
écrit :
> From: Russell King <rmk+kernel@arm.linux.org.uk>
> 
> Secondary CPU bringup typically calls calibrate_delay() during its
> initialization.  However, calibrate_delay() modifies a global variable
> (loops_per_jiffy) used for udelay() and __delay().
> 
> A side effect of 71c696b1 (calibrate: extract fall-back calculation
> into own helper) introduced in the 2.6.39 merge window means that we
> end up with a substantial period where loops_per_jiffy is zero.  This
> causes the spinlock debugging code to malfunction:
...

>  
> +	loops_per_jiffy = lpj;
>  	printed = true;
>  }

To be 100% safe, I would use

	ACCESS_ONCE(loops_per_jiffy) = lpj;

But I assume no current gcc would be that stupid ;)


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