lib/test_lockup.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Test module to generate lockups
   4  */
   5 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   6
   7 #include <linux/kernel.h>
   8 #include <linux/module.h>
   9 #include <linux/delay.h>
  10 #include <linux/sched.h>
  11 #include <linux/sched/signal.h>
  12 #include <linux/sched/clock.h>
  13 #include <linux/cpu.h>
  14 #include <linux/nmi.h>
  15 #include <linux/mm.h>
  16 #include <linux/uaccess.h>
  17 #include <linux/file.h>
  18
  19 static unsigned int time_secs;
  20 module_param(time_secs, uint, 0600);
  21 MODULE_PARM_DESC(time_secs, "lockup time in seconds, default 0");
  22
  23 static unsigned int time_nsecs;
  24 module_param(time_nsecs, uint, 0600);
  25 MODULE_PARM_DESC(time_nsecs, "nanoseconds part of lockup time, default 0");
  26
  27 static unsigned int cooldown_secs;
  28 module_param(cooldown_secs, uint, 0600);
  29 MODULE_PARM_DESC(cooldown_secs, "cooldown time between iterations in seconds, default 0");
  30
  31 static unsigned int cooldown_nsecs;
  32 module_param(cooldown_nsecs, uint, 0600);
  33 MODULE_PARM_DESC(cooldown_nsecs, "nanoseconds part of cooldown, default 0");
  34
  35 static unsigned int iterations = 1;
  36 module_param(iterations, uint, 0600);
  37 MODULE_PARM_DESC(iterations, "lockup iterations, default 1");
  38
  39 static bool all_cpus;
  40 module_param(all_cpus, bool, 0400);
  41 MODULE_PARM_DESC(all_cpus, "trigger lockup at all cpus at once");
  42
  43 static int wait_state;
  44 static char *state = "R";
  45 module_param(state, charp, 0400);
  46 MODULE_PARM_DESC(state, "wait in 'R' running (default), 'D' uninterruptible, 'K' killable, 'S' interruptible state");
  47
  48 static bool use_hrtimer;
  49 module_param(use_hrtimer, bool, 0400);
  50 MODULE_PARM_DESC(use_hrtimer, "use high-resolution timer for sleeping");
  51
  52 static bool iowait;
  53 module_param(iowait, bool, 0400);
  54 MODULE_PARM_DESC(iowait, "account sleep time as iowait");
  55
  56 static bool lock_read;
  57 module_param(lock_read, bool, 0400);
  58 MODULE_PARM_DESC(lock_read, "lock read-write locks for read");
  59
  60 static bool lock_single;
  61 module_param(lock_single, bool, 0400);
  62 MODULE_PARM_DESC(lock_single, "acquire locks only at one cpu");
  63
  64 static bool reacquire_locks;
  65 module_param(reacquire_locks, bool, 0400);
  66 MODULE_PARM_DESC(reacquire_locks, "release and reacquire locks/irq/preempt between iterations");
  67
  68 static bool touch_softlockup;
  69 module_param(touch_softlockup, bool, 0600);
  70 MODULE_PARM_DESC(touch_softlockup, "touch soft-lockup watchdog between iterations");
  71
  72 static bool touch_hardlockup;
  73 module_param(touch_hardlockup, bool, 0600);
  74 MODULE_PARM_DESC(touch_hardlockup, "touch hard-lockup watchdog between iterations");
  75
  76 static bool call_cond_resched;
  77 module_param(call_cond_resched, bool, 0600);
  78 MODULE_PARM_DESC(call_cond_resched, "call cond_resched() between iterations");
  79
  80 static bool measure_lock_wait;
  81 module_param(measure_lock_wait, bool, 0400);
  82 MODULE_PARM_DESC(measure_lock_wait, "measure lock wait time");
  83
  84 static unsigned long lock_wait_threshold = ULONG_MAX;
  85 module_param(lock_wait_threshold, ulong, 0400);
  86 MODULE_PARM_DESC(lock_wait_threshold, "print lock wait time longer than this in nanoseconds, default off");
  87
  88 static bool test_disable_irq;
  89 module_param_named(disable_irq, test_disable_irq, bool, 0400);
  90 MODULE_PARM_DESC(disable_irq, "disable interrupts: generate hard-lockups");
  91
  92 static bool disable_softirq;
  93 module_param(disable_softirq, bool, 0400);
  94 MODULE_PARM_DESC(disable_softirq, "disable bottom-half irq handlers");
  95
  96 static bool disable_preempt;
  97 module_param(disable_preempt, bool, 0400);
  98 MODULE_PARM_DESC(disable_preempt, "disable preemption: generate soft-lockups");
  99
 100 static bool lock_rcu;
 101 module_param(lock_rcu, bool, 0400);
 102 MODULE_PARM_DESC(lock_rcu, "grab rcu_read_lock: generate rcu stalls");
 103
 104 static bool lock_mmap_sem;
 105 module_param(lock_mmap_sem, bool, 0400);
 106 MODULE_PARM_DESC(lock_mmap_sem, "lock mm->mmap_lock: block procfs interfaces");
 107
 108 static unsigned long lock_rwsem_ptr;
 109 module_param_unsafe(lock_rwsem_ptr, ulong, 0400);
 110 MODULE_PARM_DESC(lock_rwsem_ptr, "lock rw_semaphore at address");
 111
 112 static unsigned long lock_mutex_ptr;
 113 module_param_unsafe(lock_mutex_ptr, ulong, 0400);
 114 MODULE_PARM_DESC(lock_mutex_ptr, "lock mutex at address");
 115
 116 static unsigned long lock_spinlock_ptr;
 117 module_param_unsafe(lock_spinlock_ptr, ulong, 0400);
 118 MODULE_PARM_DESC(lock_spinlock_ptr, "lock spinlock at address");
 119
 120 static unsigned long lock_rwlock_ptr;
 121 module_param_unsafe(lock_rwlock_ptr, ulong, 0400);
 122 MODULE_PARM_DESC(lock_rwlock_ptr, "lock rwlock at address");
 123
 124 static unsigned int alloc_pages_nr;
 125 module_param_unsafe(alloc_pages_nr, uint, 0600);
 126 MODULE_PARM_DESC(alloc_pages_nr, "allocate and free pages under locks");
 127
 128 static unsigned int alloc_pages_order;
 129 module_param(alloc_pages_order, uint, 0400);
 130 MODULE_PARM_DESC(alloc_pages_order, "page order to allocate");
 131
 132 static gfp_t alloc_pages_gfp = GFP_KERNEL;
 133 module_param_unsafe(alloc_pages_gfp, uint, 0400);
 134 MODULE_PARM_DESC(alloc_pages_gfp, "allocate pages with this gfp_mask, default GFP_KERNEL");
 135
 136 static bool alloc_pages_atomic;
 137 module_param(alloc_pages_atomic, bool, 0400);
 138 MODULE_PARM_DESC(alloc_pages_atomic, "allocate pages with GFP_ATOMIC");
 139
 140 static bool reallocate_pages;
 141 module_param(reallocate_pages, bool, 0400);
 142 MODULE_PARM_DESC(reallocate_pages, "free and allocate pages between iterations");
 143
 144 struct file *test_file;
 145 static struct inode *test_inode;
 146 static char test_file_path[256];
 147 module_param_string(file_path, test_file_path, sizeof(test_file_path), 0400);
 148 MODULE_PARM_DESC(file_path, "file path to test");
 149
 150 static bool test_lock_inode;
 151 module_param_named(lock_inode, test_lock_inode, bool, 0400);
 152 MODULE_PARM_DESC(lock_inode, "lock file -> inode -> i_rwsem");
 153
 154 static bool test_lock_mapping;
 155 module_param_named(lock_mapping, test_lock_mapping, bool, 0400);
 156 MODULE_PARM_DESC(lock_mapping, "lock file -> mapping -> i_mmap_rwsem");
 157
 158 static bool test_lock_sb_umount;
 159 module_param_named(lock_sb_umount, test_lock_sb_umount, bool, 0400);
 160 MODULE_PARM_DESC(lock_sb_umount, "lock file -> sb -> s_umount");
 161
 162 static atomic_t alloc_pages_failed = ATOMIC_INIT(0);
 163
 164 static atomic64_t max_lock_wait = ATOMIC64_INIT(0);
 165
 166 static struct task_struct *main_task;
 167 static int master_cpu;
 168
 169 static void test_lock(bool master, bool verbose)
 170 {
 171         u64 wait_start;
 172
 173         if (measure_lock_wait)
 174                 wait_start = local_clock();
 175
 176         if (lock_mutex_ptr && master) {
 177                 if (verbose)
 178                         pr_notice("lock mutex %ps\n", (void *)lock_mutex_ptr);
 179                 mutex_lock((struct mutex *)lock_mutex_ptr);
 180         }
 181
 182         if (lock_rwsem_ptr && master) {
 183                 if (verbose)
 184                         pr_notice("lock rw_semaphore %ps\n",
 185                                   (void *)lock_rwsem_ptr);
 186                 if (lock_read)
 187                         down_read((struct rw_semaphore *)lock_rwsem_ptr);
 188                 else
 189                         down_write((struct rw_semaphore *)lock_rwsem_ptr);
 190         }
 191
 192         if (lock_mmap_sem && master) {
 193                 if (verbose)
 194                         pr_notice("lock mmap_lock pid=%d\n", main_task->pid);
 195                 if (lock_read)
 196                         mmap_read_lock(main_task->mm);
 197                 else
 198                         mmap_write_lock(main_task->mm);
 199         }
 200
 201         if (test_disable_irq)
 202                 local_irq_disable();
 203
 204         if (disable_softirq)
 205                 local_bh_disable();
 206
 207         if (disable_preempt)
 208                 preempt_disable();
 209
 210         if (lock_rcu)
 211                 rcu_read_lock();
 212
 213         if (lock_spinlock_ptr && master) {
 214                 if (verbose)
 215                         pr_notice("lock spinlock %ps\n",
 216                                   (void *)lock_spinlock_ptr);
 217                 spin_lock((spinlock_t *)lock_spinlock_ptr);
 218         }
 219
 220         if (lock_rwlock_ptr && master) {
 221                 if (verbose)
 222                         pr_notice("lock rwlock %ps\n",
 223                                   (void *)lock_rwlock_ptr);
 224                 if (lock_read)
 225                         read_lock((rwlock_t *)lock_rwlock_ptr);
 226                 else
 227                         write_lock((rwlock_t *)lock_rwlock_ptr);
 228         }
 229
 230         if (measure_lock_wait) {
 231                 s64 cur_wait = local_clock() - wait_start;
 232                 s64 max_wait = atomic64_read(&max_lock_wait);
 233
 234                 do {
 235                         if (cur_wait < max_wait)
 236                                 break;
 237                         max_wait = atomic64_cmpxchg(&max_lock_wait,
 238                                                     max_wait, cur_wait);
 239                 } while (max_wait != cur_wait);
 240
 241                 if (cur_wait > lock_wait_threshold)
 242                         pr_notice_ratelimited("lock wait %lld ns\n", cur_wait);
 243         }
 244 }
 245
 246 static void test_unlock(bool master, bool verbose)
 247 {
 248         if (lock_rwlock_ptr && master) {
 249                 if (lock_read)
 250                         read_unlock((rwlock_t *)lock_rwlock_ptr);
 251                 else
 252                         write_unlock((rwlock_t *)lock_rwlock_ptr);
 253                 if (verbose)
 254                         pr_notice("unlock rwlock %ps\n",
 255                                   (void *)lock_rwlock_ptr);
 256         }
 257
 258         if (lock_spinlock_ptr && master) {
 259                 spin_unlock((spinlock_t *)lock_spinlock_ptr);
 260                 if (verbose)
 261                         pr_notice("unlock spinlock %ps\n",
 262                                   (void *)lock_spinlock_ptr);
 263         }
 264
 265         if (lock_rcu)
 266                 rcu_read_unlock();
 267
 268         if (disable_preempt)
 269                 preempt_enable();
 270
 271         if (disable_softirq)
 272                 local_bh_enable();
 273
 274         if (test_disable_irq)
 275                 local_irq_enable();
 276
 277         if (lock_mmap_sem && master) {
 278                 if (lock_read)
 279                         mmap_read_unlock(main_task->mm);
 280                 else
 281                         mmap_write_unlock(main_task->mm);
 282                 if (verbose)
 283                         pr_notice("unlock mmap_lock pid=%d\n", main_task->pid);
 284         }
 285
 286         if (lock_rwsem_ptr && master) {
 287                 if (lock_read)
 288                         up_read((struct rw_semaphore *)lock_rwsem_ptr);
 289                 else
 290                         up_write((struct rw_semaphore *)lock_rwsem_ptr);
 291                 if (verbose)
 292                         pr_notice("unlock rw_semaphore %ps\n",
 293                                   (void *)lock_rwsem_ptr);
 294         }
 295
 296         if (lock_mutex_ptr && master) {
 297                 mutex_unlock((struct mutex *)lock_mutex_ptr);
 298                 if (verbose)
 299                         pr_notice("unlock mutex %ps\n",
 300                                   (void *)lock_mutex_ptr);
 301         }
 302 }
 303
 304 static void test_alloc_pages(struct list_head *pages)
 305 {
 306         struct page *page;
 307         unsigned int i;
 308
 309         for (i = 0; i < alloc_pages_nr; i++) {
 310                 page = alloc_pages(alloc_pages_gfp, alloc_pages_order);
 311                 if (!page) {
 312                         atomic_inc(&alloc_pages_failed);
 313                         break;
 314                 }
 315                 list_add(&page->lru, pages);
 316         }
 317 }
 318
 319 static void test_free_pages(struct list_head *pages)
 320 {
 321         struct page *page, *next;
 322
 323         list_for_each_entry_safe(page, next, pages, lru)
 324                 __free_pages(page, alloc_pages_order);
 325         INIT_LIST_HEAD(pages);
 326 }
 327
 328 static void test_wait(unsigned int secs, unsigned int nsecs)
 329 {
 330         if (wait_state == TASK_RUNNING) {
 331                 if (secs)
 332                         mdelay(secs * MSEC_PER_SEC);
 333                 if (nsecs)
 334                         ndelay(nsecs);
 335                 return;
 336         }
 337
 338         __set_current_state(wait_state);
 339         if (use_hrtimer) {
 340                 ktime_t time;
 341
 342                 time = ns_to_ktime((u64)secs * NSEC_PER_SEC + nsecs);
 343                 schedule_hrtimeout(&time, HRTIMER_MODE_REL);
 344         } else {
 345                 schedule_timeout(secs * HZ + nsecs_to_jiffies(nsecs));
 346         }
 347 }
 348
 349 static void test_lockup(bool master)
 350 {
 351         u64 lockup_start = local_clock();
 352         unsigned int iter = 0;
 353         LIST_HEAD(pages);
 354
 355         pr_notice("Start on CPU%d\n", raw_smp_processor_id());
 356
 357         test_lock(master, true);
 358
 359         test_alloc_pages(&pages);
 360
 361         while (iter++ < iterations && !signal_pending(main_task)) {
 362
 363                 if (iowait)
 364                         current->in_iowait = 1;
 365
 366                 test_wait(time_secs, time_nsecs);
 367
 368                 if (iowait)
 369                         current->in_iowait = 0;
 370
 371                 if (reallocate_pages)
 372                         test_free_pages(&pages);
 373
 374                 if (reacquire_locks)
 375                         test_unlock(master, false);
 376
 377                 if (touch_softlockup)
 378                         touch_softlockup_watchdog();
 379
 380                 if (touch_hardlockup)
 381                         touch_nmi_watchdog();
 382
 383                 if (call_cond_resched)
 384                         cond_resched();
 385
 386                 test_wait(cooldown_secs, cooldown_nsecs);
 387
 388                 if (reacquire_locks)
 389                         test_lock(master, false);
 390
 391                 if (reallocate_pages)
 392                         test_alloc_pages(&pages);
 393         }
 394
 395         pr_notice("Finish on CPU%d in %lld ns\n", raw_smp_processor_id(),
 396                   local_clock() - lockup_start);
 397
 398         test_free_pages(&pages);
 399
 400         test_unlock(master, true);
 401 }
 402
 403 static DEFINE_PER_CPU(struct work_struct, test_works);
 404
 405 static void test_work_fn(struct work_struct *work)
 406 {
 407         test_lockup(!lock_single ||
 408                     work == per_cpu_ptr(&test_works, master_cpu));
 409 }
 410
 411 static bool test_kernel_ptr(unsigned long addr, int size)
 412 {
 413         void *ptr = (void *)addr;
 414         char buf;
 415
 416         if (!addr)
 417                 return false;
 418
 419         /* should be at least readable kernel address */
 420         if (!IS_ENABLED(CONFIG_ALTERNATE_USER_ADDRESS_SPACE) &&
 421             (access_ok((void __user *)ptr, 1) ||
 422              access_ok((void __user *)ptr + size - 1, 1))) {
 423                 pr_err("user space ptr invalid in kernel: %#lx\n", addr);
 424                 return true;
 425         }
 426
 427         if (get_kernel_nofault(buf, ptr) ||
 428             get_kernel_nofault(buf, ptr + size - 1)) {
 429                 pr_err("invalid kernel ptr: %#lx\n", addr);
 430                 return true;
 431         }
 432
 433         return false;
 434 }
 435
 436 static bool __maybe_unused test_magic(unsigned long addr, int offset,
 437                                       unsigned int expected)
 438 {
 439         void *ptr = (void *)addr + offset;
 440         unsigned int magic = 0;
 441
 442         if (!addr)
 443                 return false;
 444
 445         if (get_kernel_nofault(magic, ptr) || magic != expected) {
 446                 pr_err("invalid magic at %#lx + %#x = %#x, expected %#x\n",
 447                        addr, offset, magic, expected);
 448                 return true;
 449         }
 450
 451         return false;
 452 }
 453
 454 static int __init test_lockup_init(void)
 455 {
 456         u64 test_start = local_clock();
 457
 458         main_task = current;
 459
 460         switch (state[0]) {
 461         case 'S':
 462                 wait_state = TASK_INTERRUPTIBLE;
 463                 break;
 464         case 'D':
 465                 wait_state = TASK_UNINTERRUPTIBLE;
 466                 break;
 467         case 'K':
 468                 wait_state = TASK_KILLABLE;
 469                 break;
 470         case 'R':
 471                 wait_state = TASK_RUNNING;
 472                 break;
 473         default:
 474                 pr_err("unknown state=%s\n", state);
 475                 return -EINVAL;
 476         }
 477
 478         if (alloc_pages_atomic)
 479                 alloc_pages_gfp = GFP_ATOMIC;
 480
 481         if (test_kernel_ptr(lock_spinlock_ptr, sizeof(spinlock_t)) ||
 482             test_kernel_ptr(lock_rwlock_ptr, sizeof(rwlock_t)) ||
 483             test_kernel_ptr(lock_mutex_ptr, sizeof(struct mutex)) ||
 484             test_kernel_ptr(lock_rwsem_ptr, sizeof(struct rw_semaphore)))
 485                 return -EINVAL;
 486
 487 #ifdef CONFIG_DEBUG_SPINLOCK
 488 #ifdef CONFIG_PREEMPT_RT
 489         if (test_magic(lock_spinlock_ptr,
 490                        offsetof(spinlock_t, lock.wait_lock.magic),
 491                        SPINLOCK_MAGIC) ||
 492             test_magic(lock_rwlock_ptr,
 493                        offsetof(rwlock_t, rwbase.rtmutex.wait_lock.magic),
 494                        SPINLOCK_MAGIC) ||
 495             test_magic(lock_mutex_ptr,
 496                        offsetof(struct mutex, rtmutex.wait_lock.magic),
 497                        SPINLOCK_MAGIC) ||
 498             test_magic(lock_rwsem_ptr,
 499                        offsetof(struct rw_semaphore, rwbase.rtmutex.wait_lock.magic),
 500                        SPINLOCK_MAGIC))
 501                 return -EINVAL;
 502 #else
 503         if (test_magic(lock_spinlock_ptr,
 504                        offsetof(spinlock_t, rlock.magic),
 505                        SPINLOCK_MAGIC) ||
 506             test_magic(lock_rwlock_ptr,
 507                        offsetof(rwlock_t, magic),
 508                        RWLOCK_MAGIC) ||
 509             test_magic(lock_mutex_ptr,
 510                        offsetof(struct mutex, wait_lock.magic),
 511                        SPINLOCK_MAGIC) ||
 512             test_magic(lock_rwsem_ptr,
 513                        offsetof(struct rw_semaphore, wait_lock.magic),
 514                        SPINLOCK_MAGIC))
 515                 return -EINVAL;
 516 #endif
 517 #endif
 518
 519         if ((wait_state != TASK_RUNNING ||
 520              (call_cond_resched && !reacquire_locks) ||
 521              (alloc_pages_nr && gfpflags_allow_blocking(alloc_pages_gfp))) &&
 522             (test_disable_irq || disable_softirq || disable_preempt ||
 523              lock_rcu || lock_spinlock_ptr || lock_rwlock_ptr)) {
 524                 pr_err("refuse to sleep in atomic context\n");
 525                 return -EINVAL;
 526         }
 527
 528         if (lock_mmap_sem && !main_task->mm) {
 529                 pr_err("no mm to lock mmap_lock\n");
 530                 return -EINVAL;
 531         }
 532
 533         if (test_file_path[0]) {
 534                 test_file = filp_open(test_file_path, O_RDONLY, 0);
 535                 if (IS_ERR(test_file)) {
 536                         pr_err("failed to open %s: %ld\n", test_file_path, PTR_ERR(test_file));
 537                         return PTR_ERR(test_file);
 538                 }
 539                 test_inode = file_inode(test_file);
 540         } else if (test_lock_inode ||
 541                    test_lock_mapping ||
 542                    test_lock_sb_umount) {
 543                 pr_err("no file to lock\n");
 544                 return -EINVAL;
 545         }
 546
 547         if (test_lock_inode && test_inode)
 548                 lock_rwsem_ptr = (unsigned long)&test_inode->i_rwsem;
 549
 550         if (test_lock_mapping && test_file && test_file->f_mapping)
 551                 lock_rwsem_ptr = (unsigned long)&test_file->f_mapping->i_mmap_rwsem;
 552
 553         if (test_lock_sb_umount && test_inode)
 554                 lock_rwsem_ptr = (unsigned long)&test_inode->i_sb->s_umount;
 555
 556         pr_notice("START pid=%d time=%u +%u ns cooldown=%u +%u ns iterations=%u state=%s %s%s%s%s%s%s%s%s%s%s%s\n",
 557                   main_task->pid, time_secs, time_nsecs,
 558                   cooldown_secs, cooldown_nsecs, iterations, state,
 559                   all_cpus ? "all_cpus " : "",
 560                   iowait ? "iowait " : "",
 561                   test_disable_irq ? "disable_irq " : "",
 562                   disable_softirq ? "disable_softirq " : "",
 563                   disable_preempt ? "disable_preempt " : "",
 564                   lock_rcu ? "lock_rcu " : "",
 565                   lock_read ? "lock_read " : "",
 566                   touch_softlockup ? "touch_softlockup " : "",
 567                   touch_hardlockup ? "touch_hardlockup " : "",
 568                   call_cond_resched ? "call_cond_resched " : "",
 569                   reacquire_locks ? "reacquire_locks " : "");
 570
 571         if (alloc_pages_nr)
 572                 pr_notice("ALLOCATE PAGES nr=%u order=%u gfp=%pGg %s\n",
 573                           alloc_pages_nr, alloc_pages_order, &alloc_pages_gfp,
 574                           reallocate_pages ? "reallocate_pages " : "");
 575
 576         if (all_cpus) {
 577                 unsigned int cpu;
 578
 579                 cpus_read_lock();
 580
 581                 preempt_disable();
 582                 master_cpu = smp_processor_id();
 583                 for_each_online_cpu(cpu) {
 584                         INIT_WORK(per_cpu_ptr(&test_works, cpu), test_work_fn);
 585                         queue_work_on(cpu, system_highpri_wq,
 586                                       per_cpu_ptr(&test_works, cpu));
 587                 }
 588                 preempt_enable();
 589
 590                 for_each_online_cpu(cpu)
 591                         flush_work(per_cpu_ptr(&test_works, cpu));
 592
 593                 cpus_read_unlock();
 594         } else {
 595                 test_lockup(true);
 596         }
 597
 598         if (measure_lock_wait)
 599                 pr_notice("Maximum lock wait: %lld ns\n",
 600                           atomic64_read(&max_lock_wait));
 601
 602         if (alloc_pages_nr)
 603                 pr_notice("Page allocation failed %u times\n",
 604                           atomic_read(&alloc_pages_failed));
 605
 606         pr_notice("FINISH in %llu ns\n", local_clock() - test_start);
 607
 608         if (test_file)
 609                 fput(test_file);
 610
 611         if (signal_pending(main_task))
 612                 return -EINTR;
 613
 614         return -EAGAIN;
 615 }
 616 module_init(test_lockup_init);
 617
 618 MODULE_LICENSE("GPL");
 619 MODULE_AUTHOR("Konstantin Khlebnikov <khlebnikov@yandex-team.ru>");
 620 MODULE_DESCRIPTION("Test module to generate lockups");