4 files changed, 54 insertions, 10 deletions

diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
index 02b3d14c0209..516527d4bc55 100644
--- a/Documentation/RCU/torture.txt
+++ b/Documentation/RCU/torture.txt
@@ -10,13 +10,20 @@ status messages via printk(), which can be examined via the dmesg
 command (perhaps grepping for "torture").  The test is started
 when the module is loaded, and stops when the module is unloaded.
 
-However, actually setting this config option to "y" results in the system
-running the test immediately upon boot, and ending only when the system
-is taken down.  Normally, one will instead want to build the system
-with CONFIG_RCU_TORTURE_TEST=m and to use modprobe and rmmod to control
-the test, perhaps using a script similar to the one shown at the end of
-this document.  Note that you will need CONFIG_MODULE_UNLOAD in order
-to be able to end the test.
+CONFIG_RCU_TORTURE_TEST_RUNNABLE
+
+It is also possible to specify CONFIG_RCU_TORTURE_TEST=y, which will
+result in the tests being loaded into the base kernel.  In this case,
+the CONFIG_RCU_TORTURE_TEST_RUNNABLE config option is used to specify
+whether the RCU torture tests are to be started immediately during
+boot or whether the /proc/sys/kernel/rcutorture_runnable file is used
+to enable them.  This /proc file can be used to repeatedly pause and
+restart the tests, regardless of the initial state specified by the
+CONFIG_RCU_TORTURE_TEST_RUNNABLE config option.
+
+You will normally -not- want to start the RCU torture tests during boot
+(and thus the default is CONFIG_RCU_TORTURE_TEST_RUNNABLE=n), but doing
+this can sometimes be useful in finding boot-time bugs.
 
 
 MODULE PARAMETERS
diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index 98ae7d168225..27003e2421c7 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -125,6 +125,13 @@ static struct list_head rcu_torture_removed;
 
 static int stutter_pause_test = 0;
 
+#if defined(MODULE) || defined(CONFIG_RCU_TORTURE_TEST_RUNNABLE)
+#define RCUTORTURE_RUNNABLE_INIT 1
+#else
+#define RCUTORTURE_RUNNABLE_INIT 0
+#endif
+int rcutorture_runnable = RCUTORTURE_RUNNABLE_INIT;
+
 /*
  * Allocate an element from the rcu_tortures pool.
  */
@@ -188,7 +195,7 @@ rcu_random(struct rcu_random_state *rrsp)
 static void
 rcu_stutter_wait(void)
 {
-        while (stutter_pause_test)
+        while (stutter_pause_test || !rcutorture_runnable)
                 schedule_timeout_interruptible(1);
 }
 
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 29116652dca8..c6887cf135c8 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -82,6 +82,9 @@ extern int maps_protect;
 extern int sysctl_stat_interval;
 extern int latencytop_enabled;
 extern int sysctl_nr_open_min, sysctl_nr_open_max;
+#ifdef CONFIG_RCU_TORTURE_TEST
+extern int rcutorture_runnable;
+#endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
 
 /* Constants used for minimum and  maximum */
 #if defined(CONFIG_DETECT_SOFTLOCKUP) || defined(CONFIG_HIGHMEM)
@@ -813,6 +816,16 @@ static struct ctl_table kern_table[] = {
                 .child          = key_sysctls,
         },
 #endif
+#ifdef CONFIG_RCU_TORTURE_TEST
+        {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "rcutorture_runnable",
+                .data           = &rcutorture_runnable,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec,
+        },
+#endif
 /*
  * NOTE: do not add new entries to this table unless you have read
  * Documentation/sysctl/ctl_unnumbered.txt
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index f51ba2fa2662..c35a86a516a0 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -537,11 +537,28 @@ config RCU_TORTURE_TEST
           on the RCU infrastructure.  The kernel module may be built
           after the fact on the running kernel to be tested, if desired.
 
-          Say Y here if you want RCU torture tests to start automatically
-          at boot time (you probably don't).
+          Say Y here if you want RCU torture tests to be built into
+          the kernel.
           Say M if you want the RCU torture tests to build as a module.
           Say N if you are unsure.
 
+config RCU_TORTURE_TEST_RUNNABLE
+        bool "torture tests for RCU runnable by default"
+        depends on RCU_TORTURE_TEST = y
+        default n
+        help
+          This option provides a way to build the RCU torture tests
+          directly into the kernel without them starting up at boot
+          time.  You can use /proc/sys/kernel/rcutorture_runnable
+          to manually override this setting.  This /proc file is
+          available only when the RCU torture tests have been built
+          into the kernel.
+
+          Say Y here if you want the RCU torture tests to start during
+          boot (you probably don't).
+          Say N here if you want the RCU torture tests to start only
+          after being manually enabled via /proc.
+
 config KPROBES_SANITY_TEST
         bool "Kprobes sanity tests"
         depends on DEBUG_KERNEL