1Kernel Lock Torture Test Operation
2
3CONFIG_LOCK_TORTURE_TEST
4
5The CONFIG LOCK_TORTURE_TEST config option provides a kernel module
6that runs torture tests on core kernel locking primitives. The kernel
7module, 'locktorture', may be built after the fact on the running
8kernel to be tested, if desired. The tests periodically output status
9messages via printk(), which can be examined via the dmesg (perhaps
10grepping for "torture").  The test is started when the module is loaded,
11and stops when the module is unloaded. This program is based on how RCU
12is tortured, via rcutorture.
13
14This torture test consists of creating a number of kernel threads which
15acquire the lock and hold it for specific amount of time, thus simulating
16different critical region behaviors. The amount of contention on the lock
17can be simulated by either enlarging this critical region hold time and/or
18creating more kthreads.
19
20
21MODULE PARAMETERS
22
23This module has the following parameters:
24
25
26	    ** Locktorture-specific **
27
28nwriters_stress   Number of kernel threads that will stress exclusive lock
29		  ownership (writers). The default value is twice the number
30		  of online CPUs.
31
32nreaders_stress   Number of kernel threads that will stress shared lock
33		  ownership (readers). The default is the same amount of writer
34		  locks. If the user did not specify nwriters_stress, then
35		  both readers and writers be the amount of online CPUs.
36
37torture_type	  Type of lock to torture. By default, only spinlocks will
38		  be tortured. This module can torture the following locks,
39		  with string values as follows:
40
41		     o "lock_busted": Simulates a buggy lock implementation.
42
43		     o "spin_lock": spin_lock() and spin_unlock() pairs.
44
45		     o "spin_lock_irq": spin_lock_irq() and spin_unlock_irq()
46					pairs.
47
48		     o "rw_lock": read/write lock() and unlock() rwlock pairs.
49
50		     o "rw_lock_irq": read/write lock_irq() and unlock_irq()
51				      rwlock pairs.
52
53		     o "mutex_lock": mutex_lock() and mutex_unlock() pairs.
54
55		     o "rwsem_lock": read/write down() and up() semaphore pairs.
56
57torture_runnable  Start locktorture at boot time in the case where the
58		  module is built into the kernel, otherwise wait for
59		  torture_runnable to be set via sysfs before starting.
60		  By default it will begin once the module is loaded.
61
62
63	    ** Torture-framework (RCU + locking) **
64
65shutdown_secs	  The number of seconds to run the test before terminating
66		  the test and powering off the system.  The default is
67		  zero, which disables test termination and system shutdown.
68		  This capability is useful for automated testing.
69
70onoff_interval	  The number of seconds between each attempt to execute a
71		  randomly selected CPU-hotplug operation.  Defaults
72		  to zero, which disables CPU hotplugging.  In
73		  CONFIG_HOTPLUG_CPU=n kernels, locktorture will silently
74		  refuse to do any CPU-hotplug operations regardless of
75		  what value is specified for onoff_interval.
76
77onoff_holdoff	  The number of seconds to wait until starting CPU-hotplug
78		  operations.  This would normally only be used when
79		  locktorture was built into the kernel and started
80		  automatically at boot time, in which case it is useful
81		  in order to avoid confusing boot-time code with CPUs
82		  coming and going. This parameter is only useful if
83		  CONFIG_HOTPLUG_CPU is enabled.
84
85stat_interval	  Number of seconds between statistics-related printk()s.
86		  By default, locktorture will report stats every 60 seconds.
87		  Setting the interval to zero causes the statistics to
88		  be printed -only- when the module is unloaded, and this
89		  is the default.
90
91stutter		  The length of time to run the test before pausing for this
92		  same period of time.  Defaults to "stutter=5", so as
93		  to run and pause for (roughly) five-second intervals.
94		  Specifying "stutter=0" causes the test to run continuously
95		  without pausing, which is the old default behavior.
96
97shuffle_interval  The number of seconds to keep the test threads affinitied
98		  to a particular subset of the CPUs, defaults to 3 seconds.
99		  Used in conjunction with test_no_idle_hz.
100
101verbose		  Enable verbose debugging printing, via printk(). Enabled
102		  by default. This extra information is mostly related to
103		  high-level errors and reports from the main 'torture'
104		  framework.
105
106
107STATISTICS
108
109Statistics are printed in the following format:
110
111spin_lock-torture: Writes:  Total: 93746064  Max/Min: 0/0   Fail: 0
112   (A)		    (B)		   (C)		  (D)	       (E)
113
114(A): Lock type that is being tortured -- torture_type parameter.
115
116(B): Number of writer lock acquisitions. If dealing with a read/write primitive
117     a second "Reads" statistics line is printed.
118
119(C): Number of times the lock was acquired.
120
121(D): Min and max number of times threads failed to acquire the lock.
122
123(E): true/false values if there were errors acquiring the lock. This should
124     -only- be positive if there is a bug in the locking primitive's
125     implementation. Otherwise a lock should never fail (i.e., spin_lock()).
126     Of course, the same applies for (C), above. A dummy example of this is
127     the "lock_busted" type.
128
129USAGE
130
131The following script may be used to torture locks:
132
133	#!/bin/sh
134
135	modprobe locktorture
136	sleep 3600
137	rmmod locktorture
138	dmesg | grep torture:
139
140The output can be manually inspected for the error flag of "!!!".
141One could of course create a more elaborate script that automatically
142checked for such errors.  The "rmmod" command forces a "SUCCESS",
143"FAILURE", or "RCU_HOTPLUG" indication to be printk()ed.  The first
144two are self-explanatory, while the last indicates that while there
145were no locking failures, CPU-hotplug problems were detected.
146
147Also see: Documentation/RCU/torture.txt
148