linux-kernel - Re: [PATCH] Fix rcutree grace-period-latency bug on small systems

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Date:	Mon, 5 Jan 2009 10:10:34 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, andi@...stfloor.org,
	snakebyte@....de, akpm@...ux-foundation.org, dvhltc@...ibm.com,
	niv@...ibm.com, manfred@...orfullife.com, laijs@...fujitsu.com
Subject: Re: [PATCH] Fix rcutree grace-period-latency bug on small systems


* Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:

> Kudos to Andi Kleen for finding a grace-period-latency problem!  The
> problem was that the special-case code for small machines never updated
> the ->signaled field to indicate that grace-period initialization had
> completed, which prevented force_quiescent_state() from ever expediting
> grace periods.  This problem resulted in grace periods extending for more
> than 20 seconds.  Not subtle.  I introduced this bug during my inspection
> process when I fixed a race between grace-period initialization and
> force_quiescent_state() execution.
> 
> The following patch properly updates the ->signaled field for the
> "small"-system case (no more than 32 CPUs for 32-bit kernels and no more
> than 64 CPUs for 64-bit kernels).
> 
> I believe that this patch should be included for 2.6.29.
> 
> Located-by: Andi Kleen <andi@...stfloor.org>
> Tested-by: Andi Kleen <andi@...stfloor.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
> 
>  rcutree.c |    1 +
>  1 file changed, 1 insertion(+)

Applied to tip/core/urgent, thanks guys!

	Ingo
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