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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-07-21 08:05:56 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-08-19 17:18:04 -0700
commit910b1b7e19a292ff685001caf1bf1a9775b771a1 (patch)
tree7ec42bf018ab62c3c2180fbe168cd6130556cb80
parent687d7a960aea46e016182c7ce346d62c4dbd0366 (diff)
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rcu: Allow RCU CPU stall warnings to be off at boot, but manually enablable
Currently, if RCU CPU stall warnings are enabled, they are enabled immediately upon boot. They can be manually disabled via /sys (and also re-enabled via /sys), and are automatically disabled upon panic. However, some users need RCU CPU stalls to be disabled at boot time, but to be enabled without rebuilding/rebooting. For example, someone running a real-time application in production might not want the additional latency of RCU CPU stall detection in normal operation, but might need to enable it at any point for fault isolation purposes. This commit therefore provides a new CONFIG_RCU_CPU_STALL_DETECTOR_RUNNABLE kernel configuration parameter that maintains the current behavior (enable at boot) by default, but allows a kernel to be configured with RCU CPU stall detection built into the kernel, but disabled at boot time. Requested-by: Clark Williams <williams@redhat.com> Requested-by: John Kacur <jkacur@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
-rw-r--r--kernel/rcutree.c2
-rw-r--r--kernel/rcutree.h6
-rw-r--r--lib/Kconfig.debug13
3 files changed, 20 insertions, 1 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 5d910beefff..5aab7dabd0d 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -144,7 +144,7 @@ module_param(qhimark, int, 0);
module_param(qlowmark, int, 0);
#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
-int rcu_cpu_stall_suppress __read_mostly;
+int rcu_cpu_stall_suppress __read_mostly = RCU_CPU_STALL_SUPPRESS_INIT;
module_param(rcu_cpu_stall_suppress, int, 0644);
#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 183ebf40531..bb4d08695c4 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -264,6 +264,12 @@ struct rcu_data {
/* scheduling clock irq */
/* before ratting on them. */
+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR_RUNNABLE
+#define RCU_CPU_STALL_SUPPRESS_INIT 0
+#else
+#define RCU_CPU_STALL_SUPPRESS_INIT 1
+#endif
+
#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index b5005b76210..52c2172dff1 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -856,6 +856,19 @@ config RCU_CPU_STALL_TIMEOUT
RCU grace period persists, additional CPU stall warnings are
printed at more widely spaced intervals.
+config RCU_CPU_STALL_DETECTOR_RUNNABLE
+ bool "RCU CPU stall checking starts automatically at boot"
+ depends on RCU_CPU_STALL_DETECTOR
+ default y
+ help
+ If set, start checking for RCU CPU stalls immediately on
+ boot. Otherwise, RCU CPU stall checking must be manually
+ enabled.
+
+ Say Y if you are unsure.
+
+ Say N if you wish to suppress RCU CPU stall checking during boot.
+
config RCU_CPU_STALL_VERBOSE
bool "Print additional per-task information for RCU_CPU_STALL_DETECTOR"
depends on RCU_CPU_STALL_DETECTOR && TREE_PREEMPT_RCU