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

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 <paulmck@linux.vnet.ibm.com>
Suggested-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent d120f65f

Documentation/RCU/torture.txt

+14 −7
Original line number Diff line number Diff line
@@ -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

kernel/rcutorture.c

+8 −1
Original line number Diff line number Diff line
@@ -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);

}

kernel/sysctl.c

+13 −0
Original line number Diff line number Diff line
@@ -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

lib/Kconfig.debug

+19 −2
Original line number Diff line number Diff line
@@ -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

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