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Date: Tue, 5 Jan 2021 16:41:33 -0800 From: paulmck@...nel.org To: linux-kernel@...r.kernel.org Cc: kernel-team@...com, "Paul E. McKenney" <paulmck@...nel.org>, John Stultz <john.stultz@...aro.org>, Thomas Gleixner <tglx@...utronix.de>, Stephen Boyd <sboyd@...nel.org>, Jonathan Corbet <corbet@....net>, Mark Rutland <Mark.Rutland@....com>, Marc Zyngier <maz@...nel.org> Subject: [PATCH RFC clocksource 4/5] clocksource: Provide a module parameter to fuzz per-CPU clock checking From: "Paul E. McKenney" <paulmck@...nel.org> Code that checks for clock desynchronization must itself be tested, so this commit creates a new clocksource.inject_delay_shift_percpu= kernel boot parameter that adds or subtracts a large value from the check read, using the specified bit of the CPU ID to determine whether to add or to subtract. Cc: John Stultz <john.stultz@...aro.org> Cc: Thomas Gleixner <tglx@...utronix.de> Cc: Stephen Boyd <sboyd@...nel.org> Cc: Jonathan Corbet <corbet@....net> Cc: Mark Rutland <Mark.Rutland@....com> Cc: Marc Zyngier <maz@...nel.org> Reported-by: Chris Mason <clm@...com> Signed-off-by: Paul E. McKenney <paulmck@...nel.org> --- Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++ kernel/time/clocksource.c | 10 +++++++++- 2 files changed, 18 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 15aa3fe..613ce32 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -593,6 +593,15 @@ times the value specified for inject_delay_freq of consecutive non-delays. + clocksource.inject_delay_shift_percpu= [KNL] + Shift count to obtain bit from CPU number to + determine whether to shift the time of the per-CPU + clock under test ahead or behind. For example, + setting this to the value four will result in + alternating groups of 16 CPUs shifting ahead and + the rest of the CPUs shifting behind. The default + value of -1 disable this type of error injection. + clocksource.max_read_retries= [KNL] Number of clocksource_watchdog() retries due to external delays before the clock will be marked diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 23bcefe..67cf41c 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -190,6 +190,8 @@ static int inject_delay_freq; module_param(inject_delay_freq, int, 0644); static int inject_delay_run = 1; module_param(inject_delay_run, int, 0644); +static int inject_delay_shift_percpu = -1; +module_param(inject_delay_shift_percpu, int, 0644); static int max_read_retries = 3; module_param(max_read_retries, int, 0644); @@ -219,8 +221,14 @@ static cpumask_t cpus_behind; static void clocksource_verify_one_cpu(void *csin) { struct clocksource *cs = (struct clocksource *)csin; + s64 delta = 0; + int sign; - __this_cpu_write(csnow_mid, cs->read(cs)); + if (inject_delay_shift_percpu >= 0) { + sign = ((smp_processor_id() >> inject_delay_shift_percpu) & 0x1) * 2 - 1; + delta = sign * NSEC_PER_SEC; + } + __this_cpu_write(csnow_mid, cs->read(cs) + delta); } static void clocksource_verify_percpu_wq(struct work_struct *unused) -- 2.9.5
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