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+==================================
+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:
+
+ - "lock_busted":
+ Simulates a buggy lock implementation.
+
+ - "spin_lock":
+ spin_lock() and spin_unlock() pairs.
+
+ - "spin_lock_irq":
+ spin_lock_irq() and spin_unlock_irq() pairs.
+
+ - "rw_lock":
+ read/write lock() and unlock() rwlock pairs.
+
+ - "rw_lock_irq":
+ read/write lock_irq() and unlock_irq()
+ rwlock pairs.
+
+ - "mutex_lock":
+ mutex_lock() and mutex_unlock() pairs.
+
+ - "rtmutex_lock":
+ rtmutex_lock() and rtmutex_unlock() pairs.
+ Kernel must have CONFIG_RT_MUTEXES=y.
+
+ - "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.
+
+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.
+
+shuffle_interval
+ The number of seconds to keep the test threads affinitized
+ 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.rst