1

lib/test_lockup: test module to generate lockups

CONFIG_TEST_LOCKUP=m adds module "test_lockup" that helps to make sure
that watchdogs and lockup detectors are working properly.

Depending on module parameters test_lockup could emulate soft or hard
lockup, "hung task", hold arbitrary lock, allocate bunch of pages.

Also it could generate series of lockups with cooling-down periods, in
this way it could be used as "ping" for locks or page allocator.  Loop
checks signals between iteration thus could be stopped by ^C.

# modinfo test_lockup
...
parm:           time_secs:lockup time in seconds, default 0 (uint)
parm:           time_nsecs:nanoseconds part of lockup time, default 0 (uint)
parm:           cooldown_secs:cooldown time between iterations in seconds, default 0 (uint)
parm:           cooldown_nsecs:nanoseconds part of cooldown, default 0 (uint)
parm:           iterations:lockup iterations, default 1 (uint)
parm:           all_cpus:trigger lockup at all cpus at once (bool)
parm:           state:wait in 'R' running (default), 'D' uninterruptible, 'K' killable, 'S' interruptible state (charp)
parm:           use_hrtimer:use high-resolution timer for sleeping (bool)
parm:           iowait:account sleep time as iowait (bool)
parm:           lock_read:lock read-write locks for read (bool)
parm:           lock_single:acquire locks only at one cpu (bool)
parm:           reacquire_locks:release and reacquire locks/irq/preempt between iterations (bool)
parm:           touch_softlockup:touch soft-lockup watchdog between iterations (bool)
parm:           touch_hardlockup:touch hard-lockup watchdog between iterations (bool)
parm:           call_cond_resched:call cond_resched() between iterations (bool)
parm:           measure_lock_wait:measure lock wait time (bool)
parm:           lock_wait_threshold:print lock wait time longer than this in nanoseconds, default off (ulong)
parm:           disable_irq:disable interrupts: generate hard-lockups (bool)
parm:           disable_softirq:disable bottom-half irq handlers (bool)
parm:           disable_preempt:disable preemption: generate soft-lockups (bool)
parm:           lock_rcu:grab rcu_read_lock: generate rcu stalls (bool)
parm:           lock_mmap_sem:lock mm->mmap_sem: block procfs interfaces (bool)
parm:           lock_rwsem_ptr:lock rw_semaphore at address (ulong)
parm:           lock_mutex_ptr:lock mutex at address (ulong)
parm:           lock_spinlock_ptr:lock spinlock at address (ulong)
parm:           lock_rwlock_ptr:lock rwlock at address (ulong)
parm:           alloc_pages_nr:allocate and free pages under locks (uint)
parm:           alloc_pages_order:page order to allocate (uint)
parm:           alloc_pages_gfp:allocate pages with this gfp_mask, default GFP_KERNEL (uint)
parm:           alloc_pages_atomic:allocate pages with GFP_ATOMIC (bool)
parm:           reallocate_pages:free and allocate pages between iterations (bool)

Parameters for locking by address are unsafe and taints kernel. With
CONFIG_DEBUG_SPINLOCK=y they at least check magics for embedded spinlocks.

Examples:

task hang in D-state:
modprobe test_lockup time_secs=1 iterations=60 state=D

task hang in io-wait D-state:
modprobe test_lockup time_secs=1 iterations=60 state=D iowait

softlockup:
modprobe test_lockup time_secs=1 iterations=60 state=R

hardlockup:
modprobe test_lockup time_secs=1 iterations=60 state=R disable_irq

system-wide hardlockup:
modprobe test_lockup time_secs=1 iterations=60 state=R \
 disable_irq all_cpus

rcu stall:
modprobe test_lockup time_secs=1 iterations=60 state=R \
 lock_rcu touch_softlockup

lock mmap_sem / block procfs interfaces:
modprobe test_lockup time_secs=1 iterations=60 state=S lock_mmap_sem

lock tasklist_lock for read / block forks:
TASKLIST_LOCK=$(awk '$3 == "tasklist_lock" {print "0x"$1}' /proc/kallsyms)
modprobe test_lockup time_secs=1 iterations=60 state=R \
 disable_irq lock_read lock_rwlock_ptr=$TASKLIST_LOCK

lock namespace_sem / block vfs mount operations:
NAMESPACE_SEM=$(awk '$3 == "namespace_sem" {print "0x"$1}' /proc/kallsyms)
modprobe test_lockup time_secs=1 iterations=60 state=S \
 lock_rwsem_ptr=$NAMESPACE_SEM

lock cgroup mutex / block cgroup operations:
CGROUP_MUTEX=$(awk '$3 == "cgroup_mutex" {print "0x"$1}' /proc/kallsyms)
modprobe test_lockup time_secs=1 iterations=60 state=S \
 lock_mutex_ptr=$CGROUP_MUTEX

ping cgroup_mutex every second and measure maximum lock wait time:
modprobe test_lockup cooldown_secs=1 iterations=60 state=S \
 lock_mutex_ptr=$CGROUP_MUTEX reacquire_locks measure_lock_wait

[linux@roeck-us.net: rename disable_irq to fix build error]
  Link: http://lkml.kernel.org/r/20200317133614.23152-1-linux@roeck-us.net
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru
Cc: Colin Ian King <colin.king@canonical.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Link: http://lkml.kernel.org/r/158132859146.2797.525923171323227836.stgit@buzz
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Konstantin Khlebnikov 2020-04-06 20:09:47 -07:00 committed by Linus Torvalds
parent f80ac98a64
commit 30428ef5d1
3 changed files with 567 additions and 0 deletions

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@ -976,6 +976,18 @@ config WQ_WATCHDOG
state. This can be configured through kernel parameter
"workqueue.watchdog_thresh" and its sysfs counterpart.
config TEST_LOCKUP
tristate "Test module to generate lockups"
help
This builds the "test_lockup" module that helps to make sure
that watchdogs and lockup detectors are working properly.
Depending on module parameters it could emulate soft or hard
lockup, "hung task", or locking arbitrary lock for a long time.
Also it could generate series of lockups with cooling-down periods.
If unsure, say N.
endmenu # "Debug lockups and hangs"
menu "Scheduler Debugging"

View File

@ -90,6 +90,7 @@ obj-$(CONFIG_TEST_OBJAGG) += test_objagg.o
obj-$(CONFIG_TEST_STACKINIT) += test_stackinit.o
obj-$(CONFIG_TEST_BLACKHOLE_DEV) += test_blackhole_dev.o
obj-$(CONFIG_TEST_MEMINIT) += test_meminit.o
obj-$(CONFIG_TEST_LOCKUP) += test_lockup.o
obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/

554
lib/test_lockup.c Normal file
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@ -0,0 +1,554 @@
// SPDX-License-Identifier: GPL-2.0
/*
* Test module to generate lockups
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/delay.h>
#include <linux/sched.h>
#include <linux/sched/signal.h>
#include <linux/sched/clock.h>
#include <linux/cpu.h>
#include <linux/nmi.h>
#include <linux/mm.h>
#include <linux/uaccess.h>
static unsigned int time_secs;
module_param(time_secs, uint, 0600);
MODULE_PARM_DESC(time_secs, "lockup time in seconds, default 0");
static unsigned int time_nsecs;
module_param(time_nsecs, uint, 0600);
MODULE_PARM_DESC(time_nsecs, "nanoseconds part of lockup time, default 0");
static unsigned int cooldown_secs;
module_param(cooldown_secs, uint, 0600);
MODULE_PARM_DESC(cooldown_secs, "cooldown time between iterations in seconds, default 0");
static unsigned int cooldown_nsecs;
module_param(cooldown_nsecs, uint, 0600);
MODULE_PARM_DESC(cooldown_nsecs, "nanoseconds part of cooldown, default 0");
static unsigned int iterations = 1;
module_param(iterations, uint, 0600);
MODULE_PARM_DESC(iterations, "lockup iterations, default 1");
static bool all_cpus;
module_param(all_cpus, bool, 0400);
MODULE_PARM_DESC(all_cpus, "trigger lockup at all cpus at once");
static int wait_state;
static char *state = "R";
module_param(state, charp, 0400);
MODULE_PARM_DESC(state, "wait in 'R' running (default), 'D' uninterruptible, 'K' killable, 'S' interruptible state");
static bool use_hrtimer;
module_param(use_hrtimer, bool, 0400);
MODULE_PARM_DESC(use_hrtimer, "use high-resolution timer for sleeping");
static bool iowait;
module_param(iowait, bool, 0400);
MODULE_PARM_DESC(iowait, "account sleep time as iowait");
static bool lock_read;
module_param(lock_read, bool, 0400);
MODULE_PARM_DESC(lock_read, "lock read-write locks for read");
static bool lock_single;
module_param(lock_single, bool, 0400);
MODULE_PARM_DESC(lock_single, "acquire locks only at one cpu");
static bool reacquire_locks;
module_param(reacquire_locks, bool, 0400);
MODULE_PARM_DESC(reacquire_locks, "release and reacquire locks/irq/preempt between iterations");
static bool touch_softlockup;
module_param(touch_softlockup, bool, 0600);
MODULE_PARM_DESC(touch_softlockup, "touch soft-lockup watchdog between iterations");
static bool touch_hardlockup;
module_param(touch_hardlockup, bool, 0600);
MODULE_PARM_DESC(touch_hardlockup, "touch hard-lockup watchdog between iterations");
static bool call_cond_resched;
module_param(call_cond_resched, bool, 0600);
MODULE_PARM_DESC(call_cond_resched, "call cond_resched() between iterations");
static bool measure_lock_wait;
module_param(measure_lock_wait, bool, 0400);
MODULE_PARM_DESC(measure_lock_wait, "measure lock wait time");
static unsigned long lock_wait_threshold = ULONG_MAX;
module_param(lock_wait_threshold, ulong, 0400);
MODULE_PARM_DESC(lock_wait_threshold, "print lock wait time longer than this in nanoseconds, default off");
static bool test_disable_irq;
module_param_named(disable_irq, test_disable_irq, bool, 0400);
MODULE_PARM_DESC(disable_irq, "disable interrupts: generate hard-lockups");
static bool disable_softirq;
module_param(disable_softirq, bool, 0400);
MODULE_PARM_DESC(disable_softirq, "disable bottom-half irq handlers");
static bool disable_preempt;
module_param(disable_preempt, bool, 0400);
MODULE_PARM_DESC(disable_preempt, "disable preemption: generate soft-lockups");
static bool lock_rcu;
module_param(lock_rcu, bool, 0400);
MODULE_PARM_DESC(lock_rcu, "grab rcu_read_lock: generate rcu stalls");
static bool lock_mmap_sem;
module_param(lock_mmap_sem, bool, 0400);
MODULE_PARM_DESC(lock_mmap_sem, "lock mm->mmap_sem: block procfs interfaces");
static unsigned long lock_rwsem_ptr;
module_param_unsafe(lock_rwsem_ptr, ulong, 0400);
MODULE_PARM_DESC(lock_rwsem_ptr, "lock rw_semaphore at address");
static unsigned long lock_mutex_ptr;
module_param_unsafe(lock_mutex_ptr, ulong, 0400);
MODULE_PARM_DESC(lock_mutex_ptr, "lock mutex at address");
static unsigned long lock_spinlock_ptr;
module_param_unsafe(lock_spinlock_ptr, ulong, 0400);
MODULE_PARM_DESC(lock_spinlock_ptr, "lock spinlock at address");
static unsigned long lock_rwlock_ptr;
module_param_unsafe(lock_rwlock_ptr, ulong, 0400);
MODULE_PARM_DESC(lock_rwlock_ptr, "lock rwlock at address");
static unsigned int alloc_pages_nr;
module_param_unsafe(alloc_pages_nr, uint, 0600);
MODULE_PARM_DESC(alloc_pages_nr, "allocate and free pages under locks");
static unsigned int alloc_pages_order;
module_param(alloc_pages_order, uint, 0400);
MODULE_PARM_DESC(alloc_pages_order, "page order to allocate");
static gfp_t alloc_pages_gfp = GFP_KERNEL;
module_param_unsafe(alloc_pages_gfp, uint, 0400);
MODULE_PARM_DESC(alloc_pages_gfp, "allocate pages with this gfp_mask, default GFP_KERNEL");
static bool alloc_pages_atomic;
module_param(alloc_pages_atomic, bool, 0400);
MODULE_PARM_DESC(alloc_pages_atomic, "allocate pages with GFP_ATOMIC");
static bool reallocate_pages;
module_param(reallocate_pages, bool, 0400);
MODULE_PARM_DESC(reallocate_pages, "free and allocate pages between iterations");
static atomic_t alloc_pages_failed = ATOMIC_INIT(0);
static atomic64_t max_lock_wait = ATOMIC64_INIT(0);
static struct task_struct *main_task;
static int master_cpu;
static void test_lock(bool master, bool verbose)
{
u64 uninitialized_var(wait_start);
if (measure_lock_wait)
wait_start = local_clock();
if (lock_mutex_ptr && master) {
if (verbose)
pr_notice("lock mutex %ps\n", (void *)lock_mutex_ptr);
mutex_lock((struct mutex *)lock_mutex_ptr);
}
if (lock_rwsem_ptr && master) {
if (verbose)
pr_notice("lock rw_semaphore %ps\n",
(void *)lock_rwsem_ptr);
if (lock_read)
down_read((struct rw_semaphore *)lock_rwsem_ptr);
else
down_write((struct rw_semaphore *)lock_rwsem_ptr);
}
if (lock_mmap_sem && master) {
if (verbose)
pr_notice("lock mmap_sem pid=%d\n", main_task->pid);
if (lock_read)
down_read(&main_task->mm->mmap_sem);
else
down_write(&main_task->mm->mmap_sem);
}
if (test_disable_irq)
local_irq_disable();
if (disable_softirq)
local_bh_disable();
if (disable_preempt)
preempt_disable();
if (lock_rcu)
rcu_read_lock();
if (lock_spinlock_ptr && master) {
if (verbose)
pr_notice("lock spinlock %ps\n",
(void *)lock_spinlock_ptr);
spin_lock((spinlock_t *)lock_spinlock_ptr);
}
if (lock_rwlock_ptr && master) {
if (verbose)
pr_notice("lock rwlock %ps\n",
(void *)lock_rwlock_ptr);
if (lock_read)
read_lock((rwlock_t *)lock_rwlock_ptr);
else
write_lock((rwlock_t *)lock_rwlock_ptr);
}
if (measure_lock_wait) {
s64 cur_wait = local_clock() - wait_start;
s64 max_wait = atomic64_read(&max_lock_wait);
do {
if (cur_wait < max_wait)
break;
max_wait = atomic64_cmpxchg(&max_lock_wait,
max_wait, cur_wait);
} while (max_wait != cur_wait);
if (cur_wait > lock_wait_threshold)
pr_notice_ratelimited("lock wait %lld ns\n", cur_wait);
}
}
static void test_unlock(bool master, bool verbose)
{
if (lock_rwlock_ptr && master) {
if (lock_read)
read_unlock((rwlock_t *)lock_rwlock_ptr);
else
write_unlock((rwlock_t *)lock_rwlock_ptr);
if (verbose)
pr_notice("unlock rwlock %ps\n",
(void *)lock_rwlock_ptr);
}
if (lock_spinlock_ptr && master) {
spin_unlock((spinlock_t *)lock_spinlock_ptr);
if (verbose)
pr_notice("unlock spinlock %ps\n",
(void *)lock_spinlock_ptr);
}
if (lock_rcu)
rcu_read_unlock();
if (disable_preempt)
preempt_enable();
if (disable_softirq)
local_bh_enable();
if (test_disable_irq)
local_irq_enable();
if (lock_mmap_sem && master) {
if (lock_read)
up_read(&main_task->mm->mmap_sem);
else
up_write(&main_task->mm->mmap_sem);
if (verbose)
pr_notice("unlock mmap_sem pid=%d\n", main_task->pid);
}
if (lock_rwsem_ptr && master) {
if (lock_read)
up_read((struct rw_semaphore *)lock_rwsem_ptr);
else
up_write((struct rw_semaphore *)lock_rwsem_ptr);
if (verbose)
pr_notice("unlock rw_semaphore %ps\n",
(void *)lock_rwsem_ptr);
}
if (lock_mutex_ptr && master) {
mutex_unlock((struct mutex *)lock_mutex_ptr);
if (verbose)
pr_notice("unlock mutex %ps\n",
(void *)lock_mutex_ptr);
}
}
static void test_alloc_pages(struct list_head *pages)
{
struct page *page;
unsigned int i;
for (i = 0; i < alloc_pages_nr; i++) {
page = alloc_pages(alloc_pages_gfp, alloc_pages_order);
if (!page) {
atomic_inc(&alloc_pages_failed);
break;
}
list_add(&page->lru, pages);
}
}
static void test_free_pages(struct list_head *pages)
{
struct page *page, *next;
list_for_each_entry_safe(page, next, pages, lru)
__free_pages(page, alloc_pages_order);
INIT_LIST_HEAD(pages);
}
static void test_wait(unsigned int secs, unsigned int nsecs)
{
if (wait_state == TASK_RUNNING) {
if (secs)
mdelay(secs * MSEC_PER_SEC);
if (nsecs)
ndelay(nsecs);
return;
}
__set_current_state(wait_state);
if (use_hrtimer) {
ktime_t time;
time = ns_to_ktime((u64)secs * NSEC_PER_SEC + nsecs);
schedule_hrtimeout(&time, HRTIMER_MODE_REL);
} else {
schedule_timeout(secs * HZ + nsecs_to_jiffies(nsecs));
}
}
static void test_lockup(bool master)
{
u64 lockup_start = local_clock();
unsigned int iter = 0;
LIST_HEAD(pages);
pr_notice("Start on CPU%d\n", raw_smp_processor_id());
test_lock(master, true);
test_alloc_pages(&pages);
while (iter++ < iterations && !signal_pending(main_task)) {
if (iowait)
current->in_iowait = 1;
test_wait(time_secs, time_nsecs);
if (iowait)
current->in_iowait = 0;
if (reallocate_pages)
test_free_pages(&pages);
if (reacquire_locks)
test_unlock(master, false);
if (touch_softlockup)
touch_softlockup_watchdog();
if (touch_hardlockup)
touch_nmi_watchdog();
if (call_cond_resched)
cond_resched();
test_wait(cooldown_secs, cooldown_nsecs);
if (reacquire_locks)
test_lock(master, false);
if (reallocate_pages)
test_alloc_pages(&pages);
}
pr_notice("Finish on CPU%d in %lld ns\n", raw_smp_processor_id(),
local_clock() - lockup_start);
test_free_pages(&pages);
test_unlock(master, true);
}
DEFINE_PER_CPU(struct work_struct, test_works);
static void test_work_fn(struct work_struct *work)
{
test_lockup(!lock_single ||
work == per_cpu_ptr(&test_works, master_cpu));
}
static bool test_kernel_ptr(unsigned long addr, int size)
{
void *ptr = (void *)addr;
char buf;
if (!addr)
return false;
/* should be at least readable kernel address */
if (access_ok(ptr, 1) ||
access_ok(ptr + size - 1, 1) ||
probe_kernel_address(ptr, buf) ||
probe_kernel_address(ptr + size - 1, buf)) {
pr_err("invalid kernel ptr: %#lx\n", addr);
return true;
}
return false;
}
static bool __maybe_unused test_magic(unsigned long addr, int offset,
unsigned int expected)
{
void *ptr = (void *)addr + offset;
unsigned int magic = 0;
if (!addr)
return false;
if (probe_kernel_address(ptr, magic) || magic != expected) {
pr_err("invalid magic at %#lx + %#x = %#x, expected %#x\n",
addr, offset, magic, expected);
return true;
}
return false;
}
static int __init test_lockup_init(void)
{
u64 test_start = local_clock();
main_task = current;
switch (state[0]) {
case 'S':
wait_state = TASK_INTERRUPTIBLE;
break;
case 'D':
wait_state = TASK_UNINTERRUPTIBLE;
break;
case 'K':
wait_state = TASK_KILLABLE;
break;
case 'R':
wait_state = TASK_RUNNING;
break;
default:
pr_err("unknown state=%s\n", state);
return -EINVAL;
}
if (alloc_pages_atomic)
alloc_pages_gfp = GFP_ATOMIC;
if (test_kernel_ptr(lock_spinlock_ptr, sizeof(spinlock_t)) ||
test_kernel_ptr(lock_rwlock_ptr, sizeof(rwlock_t)) ||
test_kernel_ptr(lock_mutex_ptr, sizeof(struct mutex)) ||
test_kernel_ptr(lock_rwsem_ptr, sizeof(struct rw_semaphore)))
return -EINVAL;
#ifdef CONFIG_DEBUG_SPINLOCK
if (test_magic(lock_spinlock_ptr,
offsetof(spinlock_t, rlock.magic),
SPINLOCK_MAGIC) ||
test_magic(lock_rwlock_ptr,
offsetof(rwlock_t, magic),
RWLOCK_MAGIC) ||
test_magic(lock_mutex_ptr,
offsetof(struct mutex, wait_lock.rlock.magic),
SPINLOCK_MAGIC) ||
test_magic(lock_rwsem_ptr,
offsetof(struct rw_semaphore, wait_lock.magic),
SPINLOCK_MAGIC))
return -EINVAL;
#endif
if ((wait_state != TASK_RUNNING ||
(call_cond_resched && !reacquire_locks) ||
(alloc_pages_nr && gfpflags_allow_blocking(alloc_pages_gfp))) &&
(test_disable_irq || disable_softirq || disable_preempt ||
lock_rcu || lock_spinlock_ptr || lock_rwlock_ptr)) {
pr_err("refuse to sleep in atomic context\n");
return -EINVAL;
}
if (lock_mmap_sem && !main_task->mm) {
pr_err("no mm to lock mmap_sem\n");
return -EINVAL;
}
pr_notice("START pid=%d time=%u +%u ns cooldown=%u +%u ns iteraions=%u state=%s %s%s%s%s%s%s%s%s%s%s%s\n",
main_task->pid, time_secs, time_nsecs,
cooldown_secs, cooldown_nsecs, iterations, state,
all_cpus ? "all_cpus " : "",
iowait ? "iowait " : "",
test_disable_irq ? "disable_irq " : "",
disable_softirq ? "disable_softirq " : "",
disable_preempt ? "disable_preempt " : "",
lock_rcu ? "lock_rcu " : "",
lock_read ? "lock_read " : "",
touch_softlockup ? "touch_softlockup " : "",
touch_hardlockup ? "touch_hardlockup " : "",
call_cond_resched ? "call_cond_resched " : "",
reacquire_locks ? "reacquire_locks " : "");
if (alloc_pages_nr)
pr_notice("ALLOCATE PAGES nr=%u order=%u gfp=%pGg %s\n",
alloc_pages_nr, alloc_pages_order, &alloc_pages_gfp,
reallocate_pages ? "reallocate_pages " : "");
if (all_cpus) {
unsigned int cpu;
cpus_read_lock();
preempt_disable();
master_cpu = smp_processor_id();
for_each_online_cpu(cpu) {
INIT_WORK(per_cpu_ptr(&test_works, cpu), test_work_fn);
queue_work_on(cpu, system_highpri_wq,
per_cpu_ptr(&test_works, cpu));
}
preempt_enable();
for_each_online_cpu(cpu)
flush_work(per_cpu_ptr(&test_works, cpu));
cpus_read_unlock();
} else {
test_lockup(true);
}
if (measure_lock_wait)
pr_notice("Maximum lock wait: %lld ns\n",
atomic64_read(&max_lock_wait));
if (alloc_pages_nr)
pr_notice("Page allocation failed %u times\n",
atomic_read(&alloc_pages_failed));
pr_notice("FINISH in %llu ns\n", local_clock() - test_start);
if (signal_pending(main_task))
return -EINTR;
return -EAGAIN;
}
module_init(test_lockup_init);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Konstantin Khlebnikov <khlebnikov@yandex-team.ru>");
MODULE_DESCRIPTION("Test module to generate lockups");