Messages in this thread Patch in this message | | | Date | Thu, 13 May 2021 11:29:47 +0800 | From | Feng Tang <> | Subject | Re: [PATCH v14 clocksource 5/6] clocksource: Provide kernel module to test clocksource watchdog |
| |
On Tue, May 11, 2021 at 04:34:54PM -0700, Paul E. McKenney wrote: > 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.
I tried the kvm rcutorture way: "tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 45s --configs TREE03 --kconfig "CONFIG_TEST_CLOCKSOURCE_WATCHDOG=y" --bootargs "clo +cksource.max_cswd_read_retries=1" --trust-make > /tmp/kvm.sh.out 2>&1"
Also I run it through a baremetal laptop with and without "nohpet" in kernel cmdline. The debug messages from this module all look as expected, so
Tested-by: Feng Tang <feng.tang@intel.com>
Thanks, Feng
> Link: https://lore.kernel.org/lkml/202104291438.PuHsxRkl-lkp@intel.com/ > Link: https://lore.kernel.org/lkml/20210429140440.GT975577@paulmck-ThinkPad-P17-Gen-1 > Link: https://lore.kernel.org/lkml/20210425224540.GA1312438@paulmck-ThinkPad-P17-Gen-1/ > Link: https://lore.kernel.org/lkml/20210420064934.GE31773@xsang-OptiPlex-9020/ > Link: https://lore.kernel.org/lkml/20210106004013.GA11179@paulmck-ThinkPad-P72/ > Link: https://lore.kernel.org/lkml/20210414043435.GA2812539@paulmck-ThinkPad-P17-Gen-1/ > Link: https://lore.kernel.org/lkml/20210419045155.GA596058@paulmck-ThinkPad-P17-Gen-1/ > Suggested-by: Thomas Gleixner <tglx@linutronix.de> > Cc: John Stultz <john.stultz@linaro.org> > Cc: Stephen Boyd <sboyd@kernel.org> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: Mark Rutland <Mark.Rutland@arm.com> > Cc: Marc Zyngier <maz@kernel.org> > Cc: Andi Kleen <ak@linux.intel.com> > Cc: Feng Tang <feng.tang@intel.com> > Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com> > Reported-by: Chris Mason <clm@fb.com> > [ paulmck: Export clocksource_verify_percpu per kernel test robot and Stephen Rothwell. ] > Signed-off-by: Paul E. McKenney <paulmck@kernel.org> > --- > .../admin-guide/kernel-parameters.txt | 6 + > include/linux/clocksource.h | 3 + > kernel/time/Makefile | 1 + > kernel/time/clocksource-wdtest.c | 202 ++++++++++++++++++ > kernel/time/clocksource.c | 12 +- > lib/Kconfig.debug | 12 ++ > 6 files changed, 231 insertions(+), 5 deletions(-) > create mode 100644 kernel/time/clocksource-wdtest.c > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 0ef0ee743f65..9da285a98aa6 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -597,6 +597,12 @@ > The actual CPUs are chosen randomly, with > no replacement if the same CPU is chosen twice. > > + clocksource-wdtest.holdoff= [KNL] > + Set the time in seconds that the clocksource > + watchdog test waits before commencing its tests. > + Defaults to zero when built as a module and to > + 10 seconds when built into the kernel. > + > clearcpuid=BITNUM[,BITNUM...] [X86] > Disable CPUID feature X for the kernel. See > arch/x86/include/asm/cpufeatures.h for the valid bit > diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h > index 895203727cb5..1d42d4b17327 100644 > --- a/include/linux/clocksource.h > +++ b/include/linux/clocksource.h > @@ -291,4 +291,7 @@ static inline void timer_probe(void) {} > #define TIMER_ACPI_DECLARE(name, table_id, fn) \ > ACPI_DECLARE_PROBE_ENTRY(timer, name, table_id, 0, NULL, 0, fn) > > +extern ulong max_cswd_read_retries; > +void clocksource_verify_percpu(struct clocksource *cs); > + > #endif /* _LINUX_CLOCKSOURCE_H */ > diff --git a/kernel/time/Makefile b/kernel/time/Makefile > index 1fb1c1ef6a19..1ed85b25b096 100644 > --- a/kernel/time/Makefile > +++ b/kernel/time/Makefile > @@ -21,3 +21,4 @@ obj-$(CONFIG_HAVE_GENERIC_VDSO) += vsyscall.o > obj-$(CONFIG_DEBUG_FS) += timekeeping_debug.o > obj-$(CONFIG_TEST_UDELAY) += test_udelay.o > obj-$(CONFIG_TIME_NS) += namespace.o > +obj-$(CONFIG_TEST_CLOCKSOURCE_WATCHDOG) += clocksource-wdtest.o > diff --git a/kernel/time/clocksource-wdtest.c b/kernel/time/clocksource-wdtest.c > new file mode 100644 > index 000000000000..01df12395c0e > --- /dev/null > +++ b/kernel/time/clocksource-wdtest.c > @@ -0,0 +1,202 @@ > +// SPDX-License-Identifier: GPL-2.0+ > +/* > + * Unit test for the clocksource watchdog. > + * > + * Copyright (C) 2021 Facebook, Inc. > + * > + * Author: Paul E. McKenney <paulmck@kernel.org> > + */ > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt > + > +#include <linux/device.h> > +#include <linux/clocksource.h> > +#include <linux/init.h> > +#include <linux/module.h> > +#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */ > +#include <linux/tick.h> > +#include <linux/kthread.h> > +#include <linux/delay.h> > +#include <linux/prandom.h> > +#include <linux/cpu.h> > + > +MODULE_LICENSE("GPL"); > +MODULE_AUTHOR("Paul E. McKenney <paulmck@kernel.org>"); > + > +static int holdoff = IS_BUILTIN(CONFIG_TEST_CLOCKSOURCE_WATCHDOG) ? 10 : 0; > +module_param(holdoff, int, 0444); > +MODULE_PARM_DESC(holdoff, "Time to wait to start test (s)."); > + > +/* Watchdog kthread's task_struct pointer for debug purposes. */ > +static struct task_struct *wdtest_task; > + > +static u64 wdtest_jiffies_read(struct clocksource *cs) > +{ > + return (u64)jiffies; > +} > + > +/* Assume HZ > 100. */ > +#define JIFFIES_SHIFT 8 > + > +static struct clocksource clocksource_wdtest_jiffies = { > + .name = "wdtest-jiffies", > + .rating = 1, /* lowest valid rating*/ > + .uncertainty_margin = TICK_NSEC, > + .read = wdtest_jiffies_read, > + .mask = CLOCKSOURCE_MASK(32), > + .flags = CLOCK_SOURCE_MUST_VERIFY, > + .mult = TICK_NSEC << JIFFIES_SHIFT, /* details above */ > + .shift = JIFFIES_SHIFT, > + .max_cycles = 10, > +}; > + > +static int wdtest_ktime_read_ndelays; > +static bool wdtest_ktime_read_fuzz; > + > +static u64 wdtest_ktime_read(struct clocksource *cs) > +{ > + int wkrn = READ_ONCE(wdtest_ktime_read_ndelays); > + static int sign = 1; > + u64 ret; > + > + if (wkrn) { > + udelay(cs->uncertainty_margin / 250); > + WRITE_ONCE(wdtest_ktime_read_ndelays, wkrn - 1); > + } > + ret = ktime_get_real_fast_ns(); > + if (READ_ONCE(wdtest_ktime_read_fuzz)) { > + sign = -sign; > + ret = ret + sign * 100 * NSEC_PER_MSEC; > + } > + return ret; > +} > + > +static void wdtest_ktime_cs_mark_unstable(struct clocksource *cs) > +{ > + pr_info("--- Marking %s unstable due to clocksource watchdog.\n", cs->name); > +} > + > +#define KTIME_FLAGS (CLOCK_SOURCE_IS_CONTINUOUS | \ > + CLOCK_SOURCE_VALID_FOR_HRES | \ > + CLOCK_SOURCE_MUST_VERIFY | \ > + CLOCK_SOURCE_VERIFY_PERCPU) > + > +static struct clocksource clocksource_wdtest_ktime = { > + .name = "wdtest-ktime", > + .rating = 300, > + .read = wdtest_ktime_read, > + .mask = CLOCKSOURCE_MASK(64), > + .flags = KTIME_FLAGS, > + .mark_unstable = wdtest_ktime_cs_mark_unstable, > + .list = LIST_HEAD_INIT(clocksource_wdtest_ktime.list), > +}; > + > +/* Reset the clocksource if needed. */ > +static void wdtest_ktime_clocksource_reset(void) > +{ > + if (clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE) { > + clocksource_unregister(&clocksource_wdtest_ktime); > + clocksource_wdtest_ktime.flags = KTIME_FLAGS; > + schedule_timeout_uninterruptible(HZ / 10); > + clocksource_register_khz(&clocksource_wdtest_ktime, 1000 * 1000); > + } > +} > + > +/* Run the specified series of watchdog tests. */ > +static int wdtest_func(void *arg) > +{ > + unsigned long j1, j2; > + char *s; > + int i; > + > + schedule_timeout_uninterruptible(holdoff * HZ); > + > + /* > + * Verify that jiffies-like clocksources get the manually > + * specified uncertainty margin. > + */ > + pr_info("--- Verify jiffies-like uncertainty margin.\n"); > + __clocksource_register(&clocksource_wdtest_jiffies); > + WARN_ON_ONCE(clocksource_wdtest_jiffies.uncertainty_margin != TICK_NSEC); > + > + j1 = clocksource_wdtest_jiffies.read(&clocksource_wdtest_jiffies); > + schedule_timeout_uninterruptible(HZ); > + j2 = clocksource_wdtest_jiffies.read(&clocksource_wdtest_jiffies); > + WARN_ON_ONCE(j1 == j2); > + > + clocksource_unregister(&clocksource_wdtest_jiffies); > + > + /* > + * Verify that tsc-like clocksources are assigned a reasonable > + * uncertainty margin. > + */ > + pr_info("--- Verify tsc-like uncertainty margin.\n"); > + clocksource_register_khz(&clocksource_wdtest_ktime, 1000 * 1000); > + WARN_ON_ONCE(clocksource_wdtest_ktime.uncertainty_margin < NSEC_PER_USEC); > + > + j1 = clocksource_wdtest_ktime.read(&clocksource_wdtest_ktime); > + udelay(1); > + j2 = clocksource_wdtest_ktime.read(&clocksource_wdtest_ktime); > + pr_info("--- tsc-like times: %lu - %lu = %lu.\n", j2, j1, j2 - j1); > + WARN_ON_ONCE(time_before(j2, j1 + NSEC_PER_USEC)); > + > + /* Verify tsc-like stability with various numbers of errors injected. */ > + for (i = 0; i <= max_cswd_read_retries + 1; i++) { > + if (i <= 1 && i < max_cswd_read_retries) > + s = ""; > + else if (i <= max_cswd_read_retries) > + s = ", expect message"; > + else > + s = ", expect clock skew"; > + pr_info("--- Watchdog with %dx error injection, %lu retries%s.\n", i, max_cswd_read_retries, s); > + WRITE_ONCE(wdtest_ktime_read_ndelays, i); > + schedule_timeout_uninterruptible(2 * HZ); > + WARN_ON_ONCE(READ_ONCE(wdtest_ktime_read_ndelays)); > + WARN_ON_ONCE((i <= max_cswd_read_retries) != > + !(clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE)); > + wdtest_ktime_clocksource_reset(); > + } > + > + /* Verify tsc-like stability with clock-value-fuzz error injection. */ > + pr_info("--- Watchdog clock-value-fuzz error injection, expect clock skew and per-CPU mismatches.\n"); > + WRITE_ONCE(wdtest_ktime_read_fuzz, true); > + schedule_timeout_uninterruptible(2 * HZ); > + WARN_ON_ONCE(!(clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE)); > + clocksource_verify_percpu(&clocksource_wdtest_ktime); > + WRITE_ONCE(wdtest_ktime_read_fuzz, false); > + > + clocksource_unregister(&clocksource_wdtest_ktime); > + > + pr_info("--- Done with test.\n"); > + return 0; > +} > + > +static void wdtest_print_module_parms(void) > +{ > + pr_alert("--- holdoff=%d\n", holdoff); > +} > + > +/* Cleanup function. */ > +static void clocksource_wdtest_cleanup(void) > +{ > +} > + > +static int __init clocksource_wdtest_init(void) > +{ > + int ret = 0; > + > + wdtest_print_module_parms(); > + > + /* Create watchdog-test task. */ > + wdtest_task = kthread_run(wdtest_func, NULL, "wdtest"); > + if (IS_ERR(wdtest_task)) { > + ret = PTR_ERR(wdtest_task); > + pr_warn("%s: Failed to create wdtest kthread.\n", __func__); > + wdtest_task = NULL; > + return ret; > + } > + > + return 0; > +} > + > +module_init(clocksource_wdtest_init); > +module_exit(clocksource_wdtest_cleanup); > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c > index 9ebf9931f3d6..bbe1bcf44ffa 100644 > --- a/kernel/time/clocksource.c > +++ b/kernel/time/clocksource.c > @@ -199,8 +199,9 @@ void clocksource_mark_unstable(struct clocksource *cs) > spin_unlock_irqrestore(&watchdog_lock, flags); > } > > -static ulong max_read_retries = 3; > -module_param(max_read_retries, ulong, 0644); > +ulong max_cswd_read_retries = 3; > +module_param(max_cswd_read_retries, ulong, 0644); > +EXPORT_SYMBOL_GPL(max_cswd_read_retries); > static int verify_n_cpus = 8; > module_param(verify_n_cpus, int, 0644); > > @@ -210,7 +211,7 @@ static bool cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow) > u64 wd_end, wd_delta; > int64_t wd_delay; > > - for (nretries = 0; nretries <= max_read_retries; nretries++) { > + for (nretries = 0; nretries <= max_cswd_read_retries; nretries++) { > local_irq_disable(); > *wdnow = watchdog->read(watchdog); > *csnow = cs->read(cs); > @@ -220,7 +221,7 @@ static bool cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow) > wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask); > wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->shift); > if (wd_delay <= WATCHDOG_MAX_SKEW) { > - if (nretries > 1 || nretries >= max_read_retries) { > + if (nretries > 1 || nretries >= max_cswd_read_retries) { > pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n", > smp_processor_id(), watchdog->name, nretries); > } > @@ -293,7 +294,7 @@ static void clocksource_verify_one_cpu(void *csin) > csnow_mid = cs->read(cs); > } > > -static void clocksource_verify_percpu(struct clocksource *cs) > +void clocksource_verify_percpu(struct clocksource *cs) > { > int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX; > u64 csnow_begin, csnow_end; > @@ -346,6 +347,7 @@ static void clocksource_verify_percpu(struct clocksource *cs) > pr_warn(" CPU %d check durations %lldns - %lldns for clocksource %s.\n", > testcpu, cs_nsec_min, cs_nsec_max, cs->name); > } > +EXPORT_SYMBOL_GPL(clocksource_verify_percpu); > > static void clocksource_watchdog(struct timer_list *unused) > { > 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 > -- > 2.31.1.189.g2e36527f23
| |