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diff --git a/Documentation/locking/locktorture.rst b/Documentation/locking/locktorture.rst new file mode 100644 index 0000000000..3e763f77a6 --- /dev/null +++ b/Documentation/locking/locktorture.rst @@ -0,0 +1,169 @@ +================================== +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 |