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,
akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
josh@joshtriplett.org, 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,
sbw@mit.edu, patches@linaro.org,
"Paul E. McKenney" <paul.mckenney@linaro.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 01/15] rcu: Add PROVE_RCU_DELAY to provoke difficult races
Date: Thu, 30 Aug 2012 11:56:14 -0700 [thread overview]
Message-ID: <1346352988-32444-1-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <20120830185607.GA32148@linux.vnet.ibm.com>
From: "Paul E. McKenney" <paul.mckenney@linaro.org>
There have been some recent bugs that were triggered only when
preemptible RCU's __rcu_read_unlock() was preempted just after setting
->rcu_read_lock_nesting to INT_MIN, which is a low-probability event.
Therefore, reproducing those bugs (to say nothing of gaining confidence
in alleged fixes) was quite difficult. This commit therefore creates
a new debug-only RCU kernel config option that forces a short delay
in __rcu_read_unlock() to increase the probability of those sorts of
bugs occurring.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcupdate.c | 4 ++++
lib/Kconfig.debug | 14 ++++++++++++++
2 files changed, 18 insertions(+), 0 deletions(-)
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 4e6a61b..29ca1c6 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -45,6 +45,7 @@
#include <linux/mutex.h>
#include <linux/export.h>
#include <linux/hardirq.h>
+#include <linux/delay.h>
#define CREATE_TRACE_POINTS
#include <trace/events/rcu.h>
@@ -81,6 +82,9 @@ void __rcu_read_unlock(void)
} else {
barrier(); /* critical section before exit code. */
t->rcu_read_lock_nesting = INT_MIN;
+#ifdef CONFIG_PROVE_RCU_DELAY
+ udelay(10); /* Make preemption more probable. */
+#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
barrier(); /* assign before ->rcu_read_unlock_special load */
if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
rcu_read_unlock_special(t);
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 2403a63..dacbbe4 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -629,6 +629,20 @@ config PROVE_RCU_REPEATEDLY
Say N if you are unsure.
+config PROVE_RCU_DELAY
+ bool "RCU debugging: preemptible RCU race provocation"
+ depends on DEBUG_KERNEL && PREEMPT_RCU
+ default n
+ help
+ There is a class of races that involve an unlikely preemption
+ of __rcu_read_unlock() just after ->rcu_read_lock_nesting has
+ been set to INT_MIN. This feature inserts a delay at that
+ point to increase the probability of these races.
+
+ Say Y to increase probability of preemption of __rcu_read_unlock().
+
+ Say N if you are unsure.
+
config SPARSE_RCU_POINTER
bool "RCU debugging: sparse-based checks for pointer usage"
default n
--
1.7.8
next prev parent reply other threads:[~2012-08-30 21:44 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 ` Paul E. McKenney [this message]
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
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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