Commit 31a72bce authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Ingo Molnar

rcu: make rcutorture more vicious: reinstate boot-time testing

This patch re-institutes the ability to build rcutorture directly into
the Linux kernel.  The reason that this capability was removed was that
this could result in your kernel being pretty much useless, as rcutorture
would be running starting from early boot.  This problem has been avoided
by (1) making rcutorture run only three seconds of every six by default,
(2) adding a CONFIG_RCU_TORTURE_TEST_RUNNABLE that permits rcutorture
to be quiesced at boot time, and (3) adding a sysctl in /proc named
/proc/sys/kernel/rcutorture_runnable that permits rcutorture to be
quiesced and unquiesced when built into the kernel.

Please note that this /proc file is -not- available when rcutorture
is built as a module.  Please also note that to get the earlier
take-no-prisoners behavior, you must use the boot command line to set
rcutorture's "stutter" parameter to zero.

The rcutorture quiescing mechanism is currently quite crude: loops
in each rcutorture process that poll a global variable once per tick.
Suggestions for improvement are welcome.  The default action will
be to reduce the polling rate to a few times per second.
Signed-off-by: default avatarPaul E. McKenney <>
Suggested-by: default avatarIngo Molnar <>
Signed-off-by: default avatarIngo Molnar <>
parent d120f65f
......@@ -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.
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
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.
......@@ -125,6 +125,13 @@ static struct list_head rcu_torture_removed;
static int stutter_pause_test = 0;
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
while (stutter_pause_test)
while (stutter_pause_test || !rcutorture_runnable)
......@@ -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;
extern int rcutorture_runnable;
#endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
/* Constants used for minimum and maximum */
......@@ -813,6 +816,16 @@ static struct ctl_table kern_table[] = {
.child = key_sysctls,
.ctl_name = CTL_UNNUMBERED,
.procname = "rcutorture_runnable",
.data = &rcutorture_runnable,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = &proc_dointvec,
* NOTE: do not add new entries to this table unless you have read
* Documentation/sysctl/ctl_unnumbered.txt
......@@ -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.
bool "torture tests for RCU runnable by default"
depends on RCU_TORTURE_TEST = y
default n
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.
bool "Kprobes sanity tests"
depends on DEBUG_KERNEL
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