Kernel Lock Torture Test Operation
CONFIG_LOCK_TORTURE_TEST
The CONFIG LOCK_TORTURE_TEST config option provides a kernel module
that runs torture tests on core kernel locking primitives. The kernel
module, ‘locktorture’, may be built after the fact on the running
kernel to be tested, if desired. The tests periodically output status
messages via printk(), which can be examined via the dmesg (perhaps
grepping for “torture”). The test is started when the module is loaded,
and stops when the module is unloaded. This program is based on how RCU
is tortured, via rcutorture.
This torture test consists of creating a number of kernel threads which
acquire the lock and hold it for specific amount of time, thus simulating
different critical region behaviors. The amount of contention on the lock
can be simulated by either enlarging this critical region hold time and/or
creating more kthreads.
MODULE PARAMETERS
This module has the following parameters:
** Locktorture-specific **
nwriters_stress Number of kernel threads that will stress exclusive lock
ownership (writers). The default value is twice the number
of online CPUs.
nreaders_stress Number of kernel threads that will stress shared lock
ownership (readers). The default is the same amount of writer
locks. If the user did not specify nwriters_stress, then
both readers and writers be the amount of online CPUs.
torture_type Type of lock to torture. By default, only spinlocks will
be tortured. This module can torture the following locks,
with string values as follows:
o "lock_busted": Simulates a buggy lock implementation.
o "spin_lock": spin_lock() and spin_unlock() pairs.
o "spin_lock_irq": spin_lock_irq() and spin_unlock_irq()
pairs.
o "rw_lock": read/write lock() and unlock() rwlock pairs.
o "rw_lock_irq": read/write lock_irq() and unlock_irq()
rwlock pairs.
o "mutex_lock": mutex_lock() and mutex_unlock() pairs.
o "rtmutex_lock": rtmutex_lock() and rtmutex_unlock()
pairs. Kernel must have CONFIG_RT_MUTEX=y.
o "rwsem_lock": read/write down() and up() semaphore pairs.
** Torture-framework (RCU + locking) **
shutdown_secs The number of seconds to run the test before terminating
the test and powering off the system. The default is
zero, which disables test termination and system shutdown.
This capability is useful for automated testing.
onoff_interval The number of seconds between each attempt to execute a
randomly selected CPU-hotplug operation. Defaults
to zero, which disables CPU hotplugging. In
CONFIG_HOTPLUG_CPU=n kernels, locktorture will silently
refuse to do any CPU-hotplug operations regardless of
what value is specified for onoff_interval.
onoff_holdoff The number of seconds to wait until starting CPU-hotplug
operations. This would normally only be used when
locktorture was built into the kernel and started
automatically at boot time, in which case it is useful
in order to avoid confusing boot-time code with CPUs
coming and going. This parameter is only useful if
CONFIG_HOTPLUG_CPU is enabled.
stat_interval Number of seconds between statistics-related printk()s.
By default, locktorture will report stats every 60 seconds.
Setting the interval to zero causes the statistics to
be printed -only- when the module is unloaded, and this
is the default.
stutter The length of time to run the test before pausing for this
same period of time. Defaults to “stutter=5”, so as
to run and pause for (roughly) five-second intervals.
Specifying “stutter=0” causes the test to run continuously
without pausing, which is the old default behavior.
shuffle_interval The number of seconds to keep the test threads affinitied
to a particular subset of the CPUs, defaults to 3 seconds.
Used in conjunction with test_no_idle_hz.
verbose Enable verbose debugging printing, via printk(). Enabled
by default. This extra information is mostly related to
high-level errors and reports from the main ‘torture’
framework.
STATISTICS
Statistics are printed in the following format:
spin_lock-torture: Writes: Total: 93746064 Max/Min: 0/0 Fail: 0
(A) (B) (C) (D) (E)
(A): Lock type that is being tortured – torture_type parameter.
(B): Number of writer lock acquisitions. If dealing with a read/write primitive
a second “Reads” statistics line is printed.
(C): Number of times the lock was acquired.
(D): Min and max number of times threads failed to acquire the lock.
(E): true/false values if there were errors acquiring the lock. This should
-only- be positive if there is a bug in the locking primitive’s
implementation. Otherwise a lock should never fail (i.e., spin_lock()).
Of course, the same applies for (C), above. A dummy example of this is
the “lock_busted” type.
USAGE
The following script may be used to torture locks:
#!/bin/sh
modprobe locktorture
sleep 3600
rmmod locktorture
dmesg | grep torture:
The output can be manually inspected for the error flag of “!!!”.
One could of course create a more elaborate script that automatically
checked for such errors. The “rmmod” command forces a “SUCCESS”,
“FAILURE”, or “RCU_HOTPLUG” indication to be printk()ed. The first
two are self-explanatory, while the last indicates that while there
were no locking failures, CPU-hotplug problems were detected.
Also see: Documentation/RCU/torture.txt
