Date:   Tue, 11 Feb 2020 15:57:42 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Sasha Levin <sashal@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
Subject: Re: [PATCH] lib/test_lockup: test module to generate lockups

On 11/02/2020 04.26, Kees Cook wrote:
> 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 ?

Yep, LKDTM covers some cases. But they are unrecoverable.

It seems LKDTM is more like a fixed set of unit tests while
test_lockup is a flexible tool for stress load.

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

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