Re: [PATCH] Fix CPU spinlock lockups on secondary CPU bringup

From: Eric Dumazet
Date: Wed Jun 22 2011 - 12:46:56 EST

Le mercredi 22 juin 2011 Ã 11:55 +0100, Russell King - ARM Linux a
Ãcrit :
> From: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
> 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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