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From: Josh Triplett <josh@joshtriplett.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu,
	laijs@cn.fujitsu.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
	niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, Valdis.Kletnieks@vt.edu,
	dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com,
	fweisbec@gmail.com, patches@linaro.org,
	"Paul E. McKenney" <paul.mckenney@linaro.org>
Subject: Re: [PATCH RFC tip/core/rcu 38/41] rcu: Rework detection of use of RCU by offline CPUs
Date: Fri, 3 Feb 2012 01:17:36 -0800	[thread overview]
Message-ID: <20120203091736.GH3008@leaf> (raw)
In-Reply-To: <20120202183122.GC2518@linux.vnet.ibm.com>

On Thu, Feb 02, 2012 at 10:31:22AM -0800, Paul E. McKenney wrote:
> On Wed, Feb 01, 2012 at 10:11:06PM -0800, Josh Triplett wrote:
> > On Wed, Feb 01, 2012 at 11:41:56AM -0800, Paul E. McKenney wrote:
> > > From: "Paul E. McKenney" <paul.mckenney@linaro.org>
> > > 
> > > Because newly offlined CPUs continue executing after completing the
> > > CPU_DYING notifiers, they legitimately enter the scheduler and use
> > > RCU while appearing to be offline.  This calls for a more sophisticated
> > > approach as follows:
> > > 
> > > 1.	RCU marks the CPU online during the CPU_UP_PREPARE phase.
> > > 
> > > 2.	RCU marks the CPU offline during the CPU_DEAD phase.
> > > 
> > > 3.	Diagnostics regarding use of read-side RCU by offline CPUs use
> > > 	RCU's accounting rather than the cpu_online_map.  (Note that
> > > 	__call_rcu() still uses cpu_online_map to detect illegal
> > > 	invocations within CPU_DYING notifiers.)
> > > 
> > > 4.	Offline CPUs are prevented from hanging the system by
> > > 	force_quiescent_state(), which pays attention to cpu_online_map.
> > > 	Some additional work (in a later commit) will be needed to
> > > 	guarantee that force_quiescent_state() waits a full jiffy before
> > > 	assuming that a CPU is offline, for example, when called from
> > > 	idle entry.
> > > 
> > > This approach avoids the false positives encountered when attempting to
> > > use more exact classification of CPU online/offline state.
> > 
> > Doesn't this fix need to happen *before* the earlier patches in this
> > series that add splats for RCU usage while offline?  Otherwise,
> > bisection can hit those splats.
> 
> If someone actually does hit the splats during a real bisection, I will
> buy you the beverage of your choice.  ;-)

Funny, but while the likelihood of any particular bug getting hit during
bisection remains relatively low simply due to the chance of hitting
the small range of commits where it can happen, I still think it would
make sense to reorder the patch series so it can't happen at all. :)

- Josh Triplett

  reply	other threads:[~2012-02-03  9:18 UTC|newest]

Thread overview: 104+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-02-01 19:41 [PATCH RFC 0/41] RCU commits for 3.4 Paul E. McKenney
2012-02-01 19:41 ` [PATCH RFC tip/core/rcu 01/41] rcu: Bring RTFP.txt up to date Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 02/41] rcu: Improve synchronize_rcu() diagnostics Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 03/41] rcu: Add lockdep-RCU checks for simple self-deadlock Paul E. McKenney
2012-02-02  0:55     ` Josh Triplett
2012-02-02 16:20       ` Paul E. McKenney
2012-02-02 19:56         ` Josh Triplett
2012-02-02 20:42           ` Paul E. McKenney
2012-02-03  9:04             ` Josh Triplett
2012-02-03 18:05               ` Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 04/41] rcu: Add diagnostic for misaligned rcu_head structures Paul E. McKenney
2012-02-02  1:00     ` Josh Triplett
2012-02-02 16:22       ` Paul E. McKenney
2012-02-02 20:11         ` Josh Triplett
2012-02-02  1:01     ` Josh Triplett
2012-02-02 16:27       ` Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 05/41] rcu: Avoid waking up CPUs having only kfree_rcu() callbacks Paul E. McKenney
2012-02-02  1:15     ` Josh Triplett
2012-02-02 16:34       ` Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 06/41] rcu: Move RCU_TRACE to lib/Kconfig.debug Paul E. McKenney
2012-02-02  1:39     ` Josh Triplett
2012-02-02 17:05       ` Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 07/41] s390: Convert call_rcu() to kfree_rcu() Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 08/41] tcm_fc: " Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 09/41] ipv4: " Paul E. McKenney
2012-02-01 19:49     ` David Miller
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 10/41] " Paul E. McKenney
2012-02-01 19:50     ` David Miller
2012-02-02  0:24     ` Josh Triplett
2012-02-02 15:56       ` Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 11/41] mac80211: " Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 12/41] rcu: Simplify offline processing Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 13/41] rcu: Make rcutorture flag online/offline failures Paul E. McKenney
2012-02-02  1:46     ` Josh Triplett
2012-02-02 17:08       ` Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 14/41] rcu: Limit lazy-callback duration Paul E. McKenney
2012-02-02  2:03     ` Josh Triplett
2012-02-02 17:13       ` Paul E. McKenney
2012-02-03  4:07         ` Josh Triplett
2012-02-03  5:54           ` Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 15/41] rcu: Check for callback invocation from offline CPUs Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 16/41] rcu: Don't make callbacks go through second full grace period Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 17/41] rcu: Remove single-rcu_node optimization in rcu_start_gp() Paul E. McKenney
2012-02-02  2:13     ` Josh Triplett
2012-02-02 17:16       ` Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 18/41] rcu: Protect __rcu_read_unlock() against scheduler-using irq handlers Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 19/41] rcu: Streamline code produced by __rcu_read_unlock() Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 20/41] rcu: Prevent RCU callbacks from executing before scheduler initialized Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 21/41] rcu: Inform RCU of irq_exit() activity Paul E. McKenney
2012-02-02  2:30     ` Josh Triplett
2012-02-02 17:30       ` Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 22/41] rcu: Simplify unboosting checks Paul E. McKenney
2012-02-02  2:38     ` Josh Triplett
2012-02-02 17:48       ` Paul E. McKenney
2012-02-03  4:23         ` Josh Triplett
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 23/41] rcu: Clean up straggling rcu_preempt_needs_cpu() name Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 24/41] rcu: Check for idle-loop entry while in RCU read-side critical section Paul E. McKenney
2012-02-02  5:13     ` Josh Triplett
2012-02-02 17:50       ` Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 25/41] rcu: Make rcu_sleep_check() also check rcu_lock_map Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 26/41] rcu: Note that rcu_access_pointer() can be used for teardown Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 27/41] rcu: Remove #ifdef CONFIG_SMP from TREE_RCU Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 28/41] rcu: Set RCU CPU stall times via sysfs Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 29/41] rcu: Print scheduling-clock information on RCU CPU stall-warning messages Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 30/41] rcutorture: Permit holding off CPU-hotplug operations during boot Paul E. McKenney
2012-02-02  5:43     ` Josh Triplett
2012-02-02 17:56       ` Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 31/41] rcu: Add CPU-stall capability to rcutorture Paul E. McKenney
2012-02-02  5:53     ` Josh Triplett
2012-02-02  9:15       ` Julia Lawall
2012-02-02 18:03         ` Paul E. McKenney
2012-02-02 18:00       ` Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 32/41] rcu: Update stall-warning documentation Paul E. McKenney
2012-02-02  5:56     ` Josh Triplett
2012-02-02 18:18       ` Paul E. McKenney
2012-02-03  5:42         ` Josh Triplett
2012-02-03  5:58           ` Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 33/41] rcu: Make boolean rcutorture parameters be of type "bool" Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 34/41] rcu: Check for illegal use of RCU from offlined CPUs Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 35/41] rcu: Move synchronize_sched_expedited() to rcutree.c Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 36/41] rcu: No interrupt disabling for rcu_prepare_for_idle() Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 37/41] lockdep: Add CPU-idle/offline warning to lockdep-RCU splat Paul E. McKenney
2012-02-02  6:07     ` Josh Triplett
2012-02-02 18:30       ` Paul E. McKenney
2012-02-03  6:12         ` Josh Triplett
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 38/41] rcu: Rework detection of use of RCU by offline CPUs Paul E. McKenney
2012-02-02  6:11     ` Josh Triplett
2012-02-02 18:31       ` Paul E. McKenney
2012-02-03  9:17         ` Josh Triplett [this message]
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 39/41] rcu: Wait at least a jiffy before declaring a CPU to be offline Paul E. McKenney
2012-02-02  6:12     ` Josh Triplett
2012-02-02 18:27       ` Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 40/41] rcu: Call out dangers of expedited RCU primitives Paul E. McKenney
2012-02-01 19:41   ` [PATCH RFC tip/core/rcu 41/41] rcu: Trace only after NULL-pointer check Paul E. McKenney
2012-02-02  0:18   ` [PATCH RFC tip/core/rcu 01/41] rcu: Bring RTFP.txt up to date Josh Triplett
2012-02-02  1:33     ` Paul E. McKenney
2012-02-02  2:01       ` Josh Triplett
2012-02-02 16:47         ` Paul E. McKenney
2012-02-02 22:32           ` Josh Triplett
2012-02-03 18:00             ` Paul E. McKenney
2012-02-02 22:47 ` [PATCH RFC 0/41] RCU commits for 3.4 Kevin Hilman
2012-02-02 23:58   ` Paul E. McKenney
2012-02-03 19:54     ` Kevin Hilman
2012-02-06  7:04       ` Paul E. McKenney

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