From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com,
josht@linux.vnet.ibm.com, akpm@linux-foundation.org,
mathieu.desnoyers@polymtl.ca, dvhltc@us.ibm.com, niv@us.ibm.com,
tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org,
hugh.dickins@tiscali.co.uk, benh@kernel.crashing.org,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH -tip/core/rcu 4/6] Make preemptable RCU scan all CPUs when summing RCU counters.
Date: Sat, 15 Aug 2009 09:53:49 -0700 [thread overview]
Message-ID: <12503552312863-git-send-email-> (raw)
In-Reply-To: <20090815165153.GA8886@linux.vnet.ibm.com>
From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This patch eliminates the counter-moving during CPU-offline
notifiers, eliminating potential confusion if counters are
scanned during counter-movement process. This confusion
could result in premature ending of an RCU grace period.
For example, if there are two tasks in RCU read-side critical
sections (so that the sum of the counters is two), and the
counter for the CPU going offline is -2, then moving the
count to another CPU can result in the sum momentarily appearing
to be zero. Since there are no memory barriers in either case,
many more such scenarios are possible.
So just don't move the counts!!!
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcupreempt.c | 8 +-------
1 files changed, 1 insertions(+), 7 deletions(-)
diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c
index 9b87f51..2748b89 100644
--- a/kernel/rcupreempt.c
+++ b/kernel/rcupreempt.c
@@ -849,7 +849,7 @@ rcu_try_flip_waitzero(void)
/* Check to see if the sum of the "last" counters is zero. */
RCU_TRACE_ME(rcupreempt_trace_try_flip_z1);
- for_each_cpu(cpu, to_cpumask(rcu_cpu_online_map))
+ for_each_possible_cpu(cpu)
sum += RCU_DATA_CPU(cpu)->rcu_flipctr[lastidx];
if (sum != 0) {
RCU_TRACE_ME(rcupreempt_trace_try_flip_ze1);
@@ -1067,12 +1067,6 @@ void rcu_offline_cpu(int cpu)
/* seen -after- acknowledgement. */
}
- RCU_DATA_ME()->rcu_flipctr[0] += RCU_DATA_CPU(cpu)->rcu_flipctr[0];
- RCU_DATA_ME()->rcu_flipctr[1] += RCU_DATA_CPU(cpu)->rcu_flipctr[1];
-
- RCU_DATA_CPU(cpu)->rcu_flipctr[0] = 0;
- RCU_DATA_CPU(cpu)->rcu_flipctr[1] = 0;
-
cpumask_clear_cpu(cpu, to_cpumask(rcu_cpu_online_map));
spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
--
1.5.2.5
next prev parent reply other threads:[~2009-08-15 16:54 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-08-15 16:51 [PATCH -tip/core/rcu 1/6] Cleanups and fixes for RCU in face of heavy CPU-hotplug stress Paul E. McKenney
2009-08-15 16:53 ` [PATCH -tip/core/rcu 1/6] Split hierarchical RCU initialization into boot-time and CPU-online pieces Paul E. McKenney
2009-08-15 17:07 ` [tip:core/rcu] rcu: " tip-bot for Paul E. McKenney
2009-08-15 16:53 ` [PATCH -tip/core/rcu 2/6] Introduce cpu_notifier() to handle !HOTPLUG_CPU case Paul E. McKenney
2009-08-15 17:07 ` [tip:core/rcu] cpu hotplug: " tip-bot for Paul E. McKenney
2009-08-17 17:21 ` [PATCH -tip/core/rcu 2/6] " Josh Triplett
2009-08-17 18:28 ` Paul E. McKenney
2009-08-15 16:53 ` [PATCH -tip/core/rcu 3/6] Simplify RCU CPU-hotplug notification Paul E. McKenney
2009-08-15 17:07 ` [tip:core/rcu] rcu: " tip-bot for Paul E. McKenney
2009-08-20 4:02 ` [PATCH -tip/core/rcu 3/6] " Lai Jiangshan
2009-08-20 4:21 ` Paul E. McKenney
2009-08-15 16:53 ` Paul E. McKenney [this message]
2009-08-15 17:07 ` [tip:core/rcu] rcu: Make preemptable RCU scan all CPUs when summing RCU counters tip-bot for Paul E. McKenney
2009-08-15 16:53 ` [PATCH -tip/core/rcu 5/6] Make rcupreempt_trace.c look at offline CPUs Paul E. McKenney
2009-08-15 17:07 ` [tip:core/rcu] rcu: " tip-bot for Paul E. McKenney
2009-08-15 16:53 ` [PATCH -tip/core/rcu 6/6] Fix typo in rcu_irq_exit() comment header Paul E. McKenney
2009-08-15 17:00 ` Ingo Molnar
2009-08-15 17:10 ` Paul E. McKenney
2009-08-15 17:11 ` Ingo Molnar
2009-08-15 17:08 ` [tip:core/rcu] rcu: " tip-bot for Josh Triplett
2009-08-17 18:24 ` [PATCH -tip/core/rcu 1/6] Cleanups and fixes for RCU in face of heavy CPU-hotplug stress Josh Triplett
2009-08-17 19:20 ` Paul E. McKenney
2009-08-18 15:26 ` Ingo Molnar
2009-08-18 20:07 ` Paul E. McKenney
2009-08-19 6:06 ` Paul E. McKenney
2009-08-19 11:59 ` Ingo Molnar
2009-08-19 12:09 ` [tip:core/rcu] rcu: Delay rcu_barrier() wait until beginning of next CPU-hotunplug operation tip-bot for Paul E. McKenney
2009-08-19 15:24 ` [PATCH -tip/core/rcu 1/6] Cleanups and fixes for RCU in face of heavy CPU-hotplug stress Mathieu Desnoyers
2009-08-19 16:38 ` Paul E. McKenney
2009-08-19 18:10 ` Mathieu Desnoyers
2009-08-19 18:31 ` Paul E. McKenney
2009-08-20 14:03 ` Mathieu Desnoyers
2009-08-21 14:17 ` Ingo Molnar
2009-08-21 14:29 ` Steven Rostedt
2009-08-21 14:44 ` Ingo Molnar
2009-08-21 15:00 ` Mathieu Desnoyers
2009-08-21 15:37 ` Paul E. McKenney
2009-08-21 14:58 ` Mathieu Desnoyers
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