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From: Peter Zijlstra <peterz@infradead.org>
To: paulmck@linux.vnet.ibm.com
Cc: Steven Rostedt <rostedt@goodmis.org>,
	linux-kernel@vger.kernel.org, mingo@elte.hu,
	laijs@cn.fujitsu.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
	josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de,
	Valdis.Kletnieks@vt.edu, dhowells@redhat.com,
	eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com,
	sbw@mit.edu, patches@linaro.org,
	"Paul E. McKenney" <paul.mckenney@linaro.org>
Subject: Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings
Date: Fri, 07 Sep 2012 09:00:30 +0200	[thread overview]
Message-ID: <1347001230.18408.72.camel@twins> (raw)
In-Reply-To: <20120906222239.GQ2448@linux.vnet.ibm.com>

On Thu, 2012-09-06 at 15:22 -0700, Paul E. McKenney wrote:
> Ah!
> 
> It is perfectly legal to avoid -starting- an RCU grace period for a
> minute, or even longer.  If RCU has nothing to do, in other words, if no
> one registers any RCU callbacks, then RCU need not start a grace period.
> 
> Of course, this would mean that it would eventually be a full minute
> since the last start of a grace period.  This is not a problem, after
> all, Linux went through a full ten years before experiencing its first
> grace period.
> 
> But the stall-warning code just checked how long it had been since
> the last start of a grace period, failing to note that this grace
> period had long since completed.  So it splatted out a warning.
> This warning was spurious in the sense that there was no bug aside
> from the missing check that the grace period was still in progress.
> 
> And this commit fixes that bug in RCU. 

OK, that makes sense.. it just looks like both Steve and me got confused
by the initial changelog. 

  reply	other threads:[~2012-09-07  7:01 UTC|newest]

Thread overview: 86+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-30 18:56 [PATCH tip/core/rcu 0/15] Miscellaneous fixes Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 01/15] rcu: Add PROVE_RCU_DELAY to provoke difficult races Paul E. McKenney
2012-08-30 18:56   ` [PATCH tip/core/rcu 02/15] rcu: Pull TINY_RCU dyntick-idle tracing into non-idle region Paul E. McKenney
2012-08-31 16:53     ` Josh Triplett
2012-08-30 18:56   ` [PATCH tip/core/rcu 03/15] rcu: Properly initialize ->boost_tasks on CPU offline Paul E. McKenney
2012-08-31 17:56     ` Josh Triplett
2012-09-06 14:40     ` Peter Zijlstra
2012-09-06 20:58       ` Paul E. McKenney
2012-08-30 18:56   ` [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used from interrupt context Paul E. McKenney
2012-08-31 18:00     ` Josh Triplett
2012-09-04 22:33       ` Paul E. McKenney
2012-09-04 22:48         ` Josh Triplett
2012-09-04 22:51         ` Steven Rostedt
2012-09-04 23:08           ` Josh Triplett
2012-09-04 23:23             ` Steven Rostedt
2012-09-04 23:33               ` Josh Triplett
2012-09-04 23:43                 ` Paul E. McKenney
2012-09-06 18:54                   ` Josh Triplett
2012-09-06 19:54                     ` Steven Rostedt
2012-09-07  6:09                       ` Josh Triplett
2012-09-07 14:24                         ` Paul E. McKenney
2012-09-07 14:47                           ` Josh Triplett
2012-09-07 15:16                             ` Steven Rostedt
2012-09-12  1:07                               ` Paul E. McKenney
2012-09-12 14:13                                 ` Steven Rostedt
2012-09-12 15:03                                   ` Paul E. McKenney
2012-09-12 15:18                                     ` Steven Rostedt
2012-09-12 16:57                                       ` Paul E. McKenney
2012-09-04 23:46                 ` Steven Rostedt
2012-09-05  0:42                   ` Josh Triplett
2012-09-05  6:23                   ` [PATCH] trace: Don't declare trace_*_rcuidle functions in modules Josh Triplett
2012-09-05 14:26                     ` Mathieu Desnoyers
2012-09-05 16:36                     ` Paul E. McKenney
2012-09-06 19:49                     ` Steven Rostedt
2012-09-14  6:07                     ` [tip:core/rcu] trace: Don' t " tip-bot for Josh Triplett
2012-09-04 23:14           ` [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used from interrupt context Paul E. McKenney
2012-08-30 18:56   ` [PATCH tip/core/rcu 05/15] rcu: Improve boost selection when moving tasks to root rcu_node Paul E. McKenney
2012-08-31 18:09     ` Josh Triplett
2012-08-30 18:56   ` [PATCH tip/core/rcu 06/15] rcu: Make offline-CPU checking allow for indefinite delays Paul E. McKenney
2012-08-31 18:12     ` Josh Triplett
2012-08-30 18:56   ` [PATCH tip/core/rcu 07/15] rcu: Fix obsolete rcu_initiate_boost() header comment Paul E. McKenney
2012-08-31 18:13     ` Josh Triplett
2012-08-30 18:56   ` [PATCH tip/core/rcu 08/15] rcu: Apply for_each_rcu_flavor() to increment_cpu_stall_ticks() Paul E. McKenney
2012-08-31 18:15     ` Josh Triplett
2012-09-04 22:44       ` Paul E. McKenney
2012-08-30 18:56   ` [PATCH tip/core/rcu 09/15] rcu: Avoid rcu_print_detail_task_stall_rnp() segfault Paul E. McKenney
2012-08-31 18:19     ` Josh Triplett
2012-09-04 22:46       ` Paul E. McKenney
2012-09-04 22:55         ` Josh Triplett
2012-08-30 18:56   ` [PATCH tip/core/rcu 10/15] rcu: Protect rcu_node accesses during CPU stall warnings Paul E. McKenney
2012-08-31 18:23     ` Josh Triplett
2012-09-04 22:51       ` Paul E. McKenney
2012-09-06 14:51     ` Peter Zijlstra
2012-09-06 21:01       ` Paul E. McKenney
2012-08-30 18:56   ` [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU " Paul E. McKenney
2012-08-31 18:24     ` Josh Triplett
2012-09-06 14:56     ` Peter Zijlstra
2012-09-06 15:07       ` Steven Rostedt
2012-09-06 15:19         ` Peter Zijlstra
2012-09-06 21:03           ` Paul E. McKenney
2012-09-06 21:41             ` Steven Rostedt
2012-09-06 21:58               ` Paul E. McKenney
2012-09-06 22:05                 ` Steven Rostedt
2012-09-06 22:22                   ` Paul E. McKenney
2012-09-07  7:00                     ` Peter Zijlstra [this message]
2012-09-07 14:42                       ` Steven Rostedt
2012-08-30 18:56   ` [PATCH tip/core/rcu 12/15] rcu: Remove redundant memory barrier from __call_rcu() Paul E. McKenney
2012-08-31 18:30     ` Josh Triplett
2012-08-31 18:40       ` Josh Triplett
2012-08-30 18:56   ` [PATCH tip/core/rcu 13/15] rcu: Move TINY_PREEMPT_RCU away from raw_local_irq_save() Paul E. McKenney
2012-08-31 18:34     ` Josh Triplett
2012-09-04 23:03       ` Paul E. McKenney
2012-08-30 18:56   ` [PATCH tip/core/rcu 14/15] time: RCU permitted to stop idle entry via softirq Paul E. McKenney
2012-08-31 18:51     ` Josh Triplett
2012-09-06 15:12     ` Peter Zijlstra
2012-09-06 21:35       ` Paul E. McKenney
2012-09-06 21:57         ` Steven Rostedt
2012-09-06 22:11           ` Paul E. McKenney
2012-08-30 18:56   ` [PATCH tip/core/rcu 15/15] kmemleak: Replace list_for_each_continue_rcu with new interface Paul E. McKenney
2012-08-31 18:55     ` Josh Triplett
2012-09-04 23:41       ` Paul E. McKenney
2012-08-31 16:49   ` [PATCH tip/core/rcu 01/15] rcu: Add PROVE_RCU_DELAY to provoke difficult races Josh Triplett
2012-09-04 22:36     ` Paul E. McKenney
2012-09-06 14:38   ` Peter Zijlstra
2012-09-06 20:51     ` Paul E. McKenney
2012-09-07  6:54       ` Peter Zijlstra

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