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authorPaul E. McKenney <paulmck@kernel.org>2021-05-27 12:01:23 -0700
committerThomas Gleixner <tglx@linutronix.de>2021-06-22 16:53:17 +0200
commit1253b9b87e42ab6a3d5c2cb27af2bdd67d7e50ff (patch)
tree79cbd25ee67158f55202af5f1267bc30386508e8 /lib
parent2e27e793e280ff12cb5c202a1214c08b0d3a0f26 (diff)
clocksource: Provide kernel module to test clocksource watchdog
When the clocksource watchdog marks a clock as unstable, this might be due to that clock being unstable or it might be due to delays that happen to occur between the reads of the two clocks. It would be good to have a way of testing the clocksource watchdog's ability to distinguish between these two causes of clock skew and instability. Therefore, provide a new clocksource-wdtest module selected by a new TEST_CLOCKSOURCE_WATCHDOG Kconfig option. This module has a single module parameter named "holdoff" that provides the number of seconds of delay before testing should start, which defaults to zero when built as a module and to 10 seconds when built directly into the kernel. Very large systems that boot slowly may need to increase the value of this module parameter. This module uses hand-crafted clocksource structures to do its testing, thus avoiding messing up timing for the rest of the kernel and for user applications. This module first verifies that the ->uncertainty_margin field of the clocksource structures are set sanely. It then tests the delay-detection capability of the clocksource watchdog, increasing the number of consecutive delays injected, first provoking console messages complaining about the delays and finally forcing a clock-skew event. Unexpected test results cause at least one WARN_ON_ONCE() console splat. If there are no splats, the test has passed. Finally, it fuzzes the value returned from a clocksource to test the clocksource watchdog's ability to detect time skew. This module checks the state of its clocksource after each test, and uses WARN_ON_ONCE() to emit a console splat if there are any failures. This should enable all types of test frameworks to detect any such failures. This facility is intended for diagnostic use only, and should be avoided on production systems. Reported-by: Chris Mason <clm@fb.com> Suggested-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Feng Tang <feng.tang@intel.com> Link: https://lore.kernel.org/r/20210527190124.440372-5-paulmck@kernel.org
Diffstat (limited to 'lib')
-rw-r--r--lib/Kconfig.debug12
1 files changed, 12 insertions, 0 deletions
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 678c13967580..0a5a70c742e6 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2571,6 +2571,18 @@ config TEST_FPU
If unsure, say N.
+config TEST_CLOCKSOURCE_WATCHDOG
+ tristate "Test clocksource watchdog in kernel space"
+ depends on CLOCKSOURCE_WATCHDOG
+ help
+ Enable this option to create a kernel module that will trigger
+ a test of the clocksource watchdog. This module may be loaded
+ via modprobe or insmod in which case it will run upon being
+ loaded, or it may be built in, in which case it will run
+ shortly after boot.
+
+ If unsure, say N.
+
endif # RUNTIME_TESTING_MENU
config ARCH_USE_MEMTEST