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    Subject[PATCH 1/2] lib: Add module to simulate atomic sections for testing {preempt,irqs}off tracers
    Date
    From: "Joel Fernandes (Google)" <joel@joelfernandes.org>

    In this patch we introduce a test module for simulating a long atomic
    section in the kernel which the preemptoff or irqsoff tracers can
    detect. This module is to be used only for test purposes and is default
    disabled.

    Following is the expected output (only briefly shown) that can be parsed
    to verify that the tracers are working correctly. We will use this from
    the kselftests in future patches.

    For the preemptoff tracer:

    echo preemptoff > /d/tracing/current_tracer
    sleep 1
    insmod ./test_atomic_sections.ko atomic_mode=preempt atomic_time=500000
    sleep 1
    bash-4.3# cat /d/tracing/trace
    preempt -1066 2...2 0us@: atomic_sect_run <-atomic_sect_run
    preempt -1066 2...2 500002us : atomic_sect_run <-atomic_sect_run
    preempt -1066 2...2 500004us : tracer_preempt_on <-atomic_sect_run
    preempt -1066 2...2 500012us : <stack trace>
    => kthread
    => ret_from_fork

    For the irqsoff tracer:

    echo irqsoff > /d/tracing/current_tracer
    sleep 1
    insmod ./test_atomic_sections.ko atomic_mode=irq atomic_time=500000
    sleep 1
    bash-4.3# cat /d/tracing/trace
    irq dis -1069 1d..1 0us@: atomic_sect_run
    irq dis -1069 1d..1 500001us : atomic_sect_run
    irq dis -1069 1d..1 500002us : tracer_hardirqs_on <-atomic_sect_run
    irq dis -1069 1d..1 500005us : <stack trace>
    => ret_from_fork

    Co-authored-by: Erick Reyes <erickreyes@google.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Peter Zilstra <peterz@infradead.org>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: Thomas Glexiner <tglx@linutronix.de>
    Cc: Boqun Feng <boqun.feng@gmail.com>
    Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Masami Hiramatsu <mhiramat@kernel.org>
    Cc: Todd Kjos <tkjos@google.com>
    Cc: Erick Reyes <erickreyes@google.com>
    Cc: Julia Cartwright <julia@ni.com>
    Cc: kernel-team@android.com
    Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
    ---
    lib/Kconfig.debug | 9 +++++
    lib/Makefile | 1 +
    lib/test_atomic_sections.c | 80 ++++++++++++++++++++++++++++++++++++++
    3 files changed, 90 insertions(+)
    create mode 100644 lib/test_atomic_sections.c

    diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
    index c40c7b734cd1..4bb865a1f430 100644
    --- a/lib/Kconfig.debug
    +++ b/lib/Kconfig.debug
    @@ -1933,6 +1933,15 @@ config TEST_KMOD

    If unsure, say N.

    +config TEST_ATOMIC_SECTIONS
    + tristate "Simulate atomic sections for tracers to detect"
    + default n
    + depends on m
    + help
    + Select this option to build a test module that can help test atomic
    + sections by simulating them with a duration supplied as a module
    + parameter. Preempt disable and irq disable modes can be requested.
    +
    config TEST_DEBUG_VIRTUAL
    tristate "Test CONFIG_DEBUG_VIRTUAL feature"
    depends on DEBUG_VIRTUAL
    diff --git a/lib/Makefile b/lib/Makefile
    index ce20696d5a92..e82cf5445b7b 100644
    --- a/lib/Makefile
    +++ b/lib/Makefile
    @@ -46,6 +46,7 @@ obj-y += string_helpers.o
    obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
    obj-y += hexdump.o
    obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
    +obj-$(CONFIG_TEST_ATOMIC_SECTIONS) += test_atomic_sections.o
    obj-y += kstrtox.o
    obj-$(CONFIG_FIND_BIT_BENCHMARK) += find_bit_benchmark.o
    obj-$(CONFIG_TEST_BPF) += test_bpf.o
    diff --git a/lib/test_atomic_sections.c b/lib/test_atomic_sections.c
    new file mode 100644
    index 000000000000..3c8816c333c0
    --- /dev/null
    +++ b/lib/test_atomic_sections.c
    @@ -0,0 +1,80 @@
    +/*
    + * Atomic section emulation test module
    + *
    + * Emulates atomic sections by disabling IRQs or preemption
    + * and doing a busy wait for a specified amount of time.
    + * This can be used for testing of different atomic section
    + * tracers such as irqsoff tracers.
    + *
    + * (c) 2018. Google LLC
    + */
    +
    +#include <linux/kernel.h>
    +#include <linux/module.h>
    +#include <linux/ktime.h>
    +#include <linux/irq.h>
    +#include <linux/printk.h>
    +#include <linux/interrupt.h>
    +#include <linux/delay.h>
    +#include <linux/string.h>
    +#include <linux/kthread.h>
    +
    +static int atomic_time = 100;
    +static char atomic_mode[10] = "irq";
    +
    +module_param_named(atomic_time, atomic_time, int, S_IRUGO);
    +module_param_string(atomic_mode, atomic_mode, 10, S_IRUGO);
    +MODULE_PARM_DESC(atomic_time, "Period in microseconds (100 uS default)");
    +MODULE_PARM_DESC(atomic_mode, "Mode of the test such as preempt or irq (default irq)");
    +
    +static void busy_wait(int time)
    +{
    + ktime_t start, end;
    + start = ktime_get();
    + do {
    + end = ktime_get();
    + if (kthread_should_stop())
    + break;
    + } while (ktime_to_ns(ktime_sub(end, start)) < (time * 1000));
    +}
    +
    +void atomic_sect_run(void *data)
    +{
    + unsigned long flags;
    +
    + if (!strcmp(atomic_mode, "irq")) {
    + local_irq_save(flags);
    + busy_wait(atomic_time);
    + local_irq_restore(flags);
    + } else if (!strcmp(atomic_mode, "preempt")) {
    + preempt_disable();
    + busy_wait(atomic_time);
    + preempt_enable();
    + }
    + do_exit(0);
    +}
    +
    +
    +static int __init atomic_sect_init(void)
    +{
    + char task_name[50];
    + struct task_struct *test_task;
    +
    + sprintf(task_name, "%s dis test", atomic_mode);
    +
    + test_task = kthread_run((void*)atomic_sect_run, NULL, task_name);
    + if (IS_ERR(test_task)) {
    + return -1;
    + }
    +
    + return 0;
    +}
    +
    +static void __exit atomic_sect_exit(void)
    +{
    + return 0;
    +}
    +
    +module_init(atomic_sect_init)
    +module_exit(atomic_sect_exit)
    +MODULE_LICENSE("GPL");
    --
    2.17.0.441.gb46fe60e1d-goog
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