Re: [PATCH] lib/test_lockup: test module to generate lockups

[Kees Cook]

On Mon, Feb 10, 2020 at 12:56:31PM +0300, Konstantin Khlebnikov wrote:
> CONFIG_TEST_LOCKUP=m adds module "test_lockup" that helps to make sure
> that watchdogs and lockup detectors are working properly.

Isn't this all already possible with CONFIG_LKDTM ?

-Kees

> 
> 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=$CGROUP_MUTEX reacquire_locks measure_lock_wait
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
> ---
>  lib/Kconfig.debug |   12 +
>  lib/Makefile      |    1 
>  lib/test_lockup.c |  554 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 567 insertions(+)
>  create mode 100644 lib/test_lockup.c
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 69def4a9df00..8feaf71dab15 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -978,6 +978,18 @@ config WQ_WATCHDOG
>  	  state.  This can be configured through kernel parameter
>  	  "workqueue.watchdog_thresh" and its sysfs counterpart.
>  
> +config TEST_LOCKUP
> +	tristate "Test module to generate lockups"
> +	help
> +	  This builds the "test_lockup" module that helps to make sure
> +	  that watchdogs and lockup detectors are working properly.
> +
> +	  Depending on module parameters it could emulate soft or hard
> +	  lockup, "hung task", or locking arbitrary lock for a long time.
> +	  Also it could generate series of lockups with cooling-down periods.
> +
> +	  If unsure, say N.
> +
>  endmenu # "Debug lockups and hangs"
>  
>  menu "Scheduler Debugging"
> diff --git a/lib/Makefile b/lib/Makefile
> index 5d64890d6b6a..b5372a83ebe2 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -89,6 +89,7 @@ obj-$(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/
>  
> diff --git a/lib/test_lockup.c b/lib/test_lockup.c
> new file mode 100644
> index 000000000000..f91cd44ad75a
> --- /dev/null
> +++ b/lib/test_lockup.c
> @@ -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 disable_irq;
> +module_param(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 (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 (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))) &&
> +	    (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 " : "",
> +		  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@xxxxxxxxxxxxxx>");
> +MODULE_DESCRIPTION("Test module to generate lockups");
> 

-- 
Kees Cook