linux-kernel - Re: [PATCH tip/master] RCU-based detection of stalled CPUs for Classic RCU

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Date:	Fri, 3 Oct 2008 10:39:47 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mathieu.desnoyers@...ymtl.ca,
	akpm@...ux-foundation.org, laijs@...fujitsu.com,
	manfred@...orfullife.com, dipankar@...ibm.com, niv@...ibm.com,
	dvhltc@...ibm.com, josht@...ux.vnet.ibm.com,
	ltt-dev@...ts.casi.polymtl.ca
Subject: Re: [PATCH tip/master] RCU-based detection of stalled CPUs for
	Classic RCU


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

> Hello!
> 
> This patch adds stalled-CPU detection to Classic RCU.  This capability 
> is enabled by a new config variable CONFIG_RCU_CPU_STALL_DETECTOR, 
> which defaults disabled.  This is a debugging feature to detect 
> infinite loops in kernel code, not something that non-kernel-hackers 
> would be expected to care about.  This feature can detect looping CPUs 
> in !PREEMPT builds and looping CPUs with preemption disabled in 
> PREEMPT builds.  This is essentially a port of this functionality from 
> the treercu patch, replacing the stall debug patch that is already in 
> tip/core/rcu (commit 67182ae1c4).
> 
> The changes from the patch in tip/core/rcu include making the config 
> variable name match that in treercu, changing from seconds to jiffies 
> to avoid spurious warnings, and printing a boot message when this 
> feature is enabled.
> 
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

applied to tip/core/rcu, thanks Paul!

i tidied up two tiny details noticed by scripts/checkpatch.pl:

> +#define RCU_SECONDS_TILL_STALL_CHECK	3 * HZ	/* for rcp->jiffies_stall */
> +#define RCU_SECONDS_TILL_STALL_RECHECK	30 * HZ	/* for rcp->jiffies_stall */

adding paranthesis around the expression.

> +	if (cpu_isset(smp_processor_id(), rcp->cpumask) && delta >= 0) {
> +		

and have removed the two tailing tabs from this line.

	Ingo
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