alistair23-linux/kernel/trace/preemptirq_delay_test.c
Steven Rostedt (VMware) 8b1fac2e73 tracing: Wait for preempt irq delay thread to execute
A bug report was posted that running the preempt irq delay module on a slow
machine, and removing it quickly could lead to the thread created by the
modlue to execute after the module is removed, and this could cause the
kernel to crash. The fix for this was to call kthread_stop() after creating
the thread to make sure it finishes before allowing the module to be
removed.

Now this caused the opposite problem on fast machines. What now happens is
the kthread_stop() can cause the kthread never to execute and the test never
to run. To fix this, add a completion and wait for the kthread to execute,
then wait for it to end.

This issue caused the ftracetest selftests to fail on the preemptirq tests.

Link: https://lore.kernel.org/r/20200510114210.15d9e4af@oasis.local.home

Cc: stable@vger.kernel.org
Fixes: d16a8c3107 ("tracing: Wait for preempt irq delay thread to finish")
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
2020-05-11 17:00:34 -04:00

205 lines
4.2 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Preempt / IRQ disable delay thread to test latency tracers
*
* Copyright (C) 2018 Joel Fernandes (Google) <joel@joelfernandes.org>
*/
#include <linux/trace_clock.h>
#include <linux/delay.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/kernel.h>
#include <linux/kobject.h>
#include <linux/kthread.h>
#include <linux/module.h>
#include <linux/printk.h>
#include <linux/string.h>
#include <linux/sysfs.h>
#include <linux/completion.h>
static ulong delay = 100;
static char test_mode[12] = "irq";
static uint burst_size = 1;
module_param_named(delay, delay, ulong, 0444);
module_param_string(test_mode, test_mode, 12, 0444);
module_param_named(burst_size, burst_size, uint, 0444);
MODULE_PARM_DESC(delay, "Period in microseconds (100 us default)");
MODULE_PARM_DESC(test_mode, "Mode of the test such as preempt, irq, or alternate (default irq)");
MODULE_PARM_DESC(burst_size, "The size of a burst (default 1)");
static struct completion done;
#define MIN(x, y) ((x) < (y) ? (x) : (y))
static void busy_wait(ulong time)
{
u64 start, end;
start = trace_clock_local();
do {
end = trace_clock_local();
if (kthread_should_stop())
break;
} while ((end - start) < (time * 1000));
}
static __always_inline void irqoff_test(void)
{
unsigned long flags;
local_irq_save(flags);
busy_wait(delay);
local_irq_restore(flags);
}
static __always_inline void preemptoff_test(void)
{
preempt_disable();
busy_wait(delay);
preempt_enable();
}
static void execute_preemptirqtest(int idx)
{
if (!strcmp(test_mode, "irq"))
irqoff_test();
else if (!strcmp(test_mode, "preempt"))
preemptoff_test();
else if (!strcmp(test_mode, "alternate")) {
if (idx % 2 == 0)
irqoff_test();
else
preemptoff_test();
}
}
#define DECLARE_TESTFN(POSTFIX) \
static void preemptirqtest_##POSTFIX(int idx) \
{ \
execute_preemptirqtest(idx); \
} \
/*
* We create 10 different functions, so that we can get 10 different
* backtraces.
*/
DECLARE_TESTFN(0)
DECLARE_TESTFN(1)
DECLARE_TESTFN(2)
DECLARE_TESTFN(3)
DECLARE_TESTFN(4)
DECLARE_TESTFN(5)
DECLARE_TESTFN(6)
DECLARE_TESTFN(7)
DECLARE_TESTFN(8)
DECLARE_TESTFN(9)
static void (*testfuncs[])(int) = {
preemptirqtest_0,
preemptirqtest_1,
preemptirqtest_2,
preemptirqtest_3,
preemptirqtest_4,
preemptirqtest_5,
preemptirqtest_6,
preemptirqtest_7,
preemptirqtest_8,
preemptirqtest_9,
};
#define NR_TEST_FUNCS ARRAY_SIZE(testfuncs)
static int preemptirq_delay_run(void *data)
{
int i;
int s = MIN(burst_size, NR_TEST_FUNCS);
for (i = 0; i < s; i++)
(testfuncs[i])(i);
complete(&done);
set_current_state(TASK_INTERRUPTIBLE);
while (!kthread_should_stop()) {
schedule();
set_current_state(TASK_INTERRUPTIBLE);
}
__set_current_state(TASK_RUNNING);
return 0;
}
static int preemptirq_run_test(void)
{
struct task_struct *task;
char task_name[50];
init_completion(&done);
snprintf(task_name, sizeof(task_name), "%s_test", test_mode);
task = kthread_run(preemptirq_delay_run, NULL, task_name);
if (IS_ERR(task))
return PTR_ERR(task);
if (task) {
wait_for_completion(&done);
kthread_stop(task);
}
return 0;
}
static ssize_t trigger_store(struct kobject *kobj, struct kobj_attribute *attr,
const char *buf, size_t count)
{
ssize_t ret;
ret = preemptirq_run_test();
if (ret)
return ret;
return count;
}
static struct kobj_attribute trigger_attribute =
__ATTR(trigger, 0200, NULL, trigger_store);
static struct attribute *attrs[] = {
&trigger_attribute.attr,
NULL,
};
static struct attribute_group attr_group = {
.attrs = attrs,
};
static struct kobject *preemptirq_delay_kobj;
static int __init preemptirq_delay_init(void)
{
int retval;
retval = preemptirq_run_test();
if (retval != 0)
return retval;
preemptirq_delay_kobj = kobject_create_and_add("preemptirq_delay_test",
kernel_kobj);
if (!preemptirq_delay_kobj)
return -ENOMEM;
retval = sysfs_create_group(preemptirq_delay_kobj, &attr_group);
if (retval)
kobject_put(preemptirq_delay_kobj);
return retval;
}
static void __exit preemptirq_delay_exit(void)
{
kobject_put(preemptirq_delay_kobj);
}
module_init(preemptirq_delay_init)
module_exit(preemptirq_delay_exit)
MODULE_LICENSE("GPL v2");