kernel/pwqr.c

   1 /*
   2  * Copyright (C) 2012   Pierre Habouzit <pierre.habouzit@intersec.com>
   3  * Copyright (C) 2012   Intersec SAS
   4  *
   5  * This file implements the Linux Pthread Workqueue Regulator, and is part
   6  * of the linux kernel.
   7  *
   8  * The Linux Kernel is free software: you can redistribute it and/or modify it
   9  * under the terms of the GNU General Public License version 2 as published by
  10  * the Free Software Foundation.
  11  *
  12  * The Linux Kernel is distributed in the hope that it will be useful, but
  13  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  14  * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  15  * License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License version 2
  18  * along with The Linux Kernel.  If not, see <http://www.gnu.org/licenses/>.
  19  */
  20
  21 #include <linux/cdev.h>
  22 #include <linux/device.h>
  23 #include <linux/file.h>
  24 #include <linux/fs.h>
  25 #include <linux/hash.h>
  26 #include <linux/init.h>
  27 #include <linux/kref.h>
  28 #include <linux/module.h>
  29 #include <linux/poll.h>
  30 #include <linux/sched.h>
  31 #include <linux/slab.h>
  32 #include <linux/spinlock.h>
  33 #include <linux/timer.h>
  34 #include <linux/uaccess.h>
  35 #include <linux/wait.h>
  36 #include <linux/version.h>
  37
  38 /*
  39  * The pthread workqueue regulator code is for now written as a proof of
  40  * concept module, meant to work with 2.6.23+ kernels or redhat5 ones.
  41  *
  42  * For now it uses a device /dev/pwq, which spawns magic file-descriptors
  43  * supporting a few ioctl operations (see Documentation/pwqr.adoc shipped in
  44  * the same git repository).
  45  *
  46  * This code is meant to be merged into mainline, but after the following
  47  * changes, kept here as a "todolist":
  48  *
  49  *   - get rid of the device stuff (which is 100% of the init code for 2.6.23
  50  *     kernels);
  51  *
  52  *   - resubmit the patch that makes it possible to call
  53  *     preempt_notifier_unregister from sched_in/sched_out (just a matter of a
  54  *     hlist_for_each_safe instead of hlist_for_each), and fix
  55  *     pwqr_task_release to not require RCU anymore. It makes
  56  *     pwqr_preempt_noop_ops go away.
  57  *
  58  *   - think about the possibility to add a pwq_notifier pointer directly into
  59  *     the task_struct, thought it's not *that* necessary, it grows the
  60  *     structure for a speed gain we don't really need (making pwqr_ctl
  61  *     faster). I think it's okay to crawl the preempt_notifier list instead.
  62  *     We may want to add nice "macros" for that though.
  63  *
  64  *   - replace the ioctl with a pwqr_ctl syscall
  65  *
  66  *   - create a pwqr_create() syscall to create a pwqr file-descriptor.
  67  *
  68  * Summary: most of the code should be untouched or almost not changed,
  69  * pwqr_ioctl adapted to become a syscall, and the module boilerplate replaced
  70  * with pwqr_create() and file-descriptor creation boilerplate instead. But
  71  * looking at fs/eventfd.c this looks rather simple.
  72  */
  73
  74 #ifndef CONFIG_PREEMPT_NOTIFIERS
  75 #  error PWQ module requires CONFIG_PREEMPT_NOTIFIERS
  76 #else
  77
  78 #include "pwqr.h"
  79
  80 #define PWQR_UC_DELAY           (HZ / 10)
  81 #define PWQR_OC_DELAY           (HZ / 20)
  82
  83 #define PWQR_STATE_NONE         0
  84 #define PWQR_STATE_UC           1
  85 #define PWQR_STATE_OC           2
  86 #define PWQR_STATE_DEAD         (-1)
  87
  88 /*
  89  * This is the first inclusion of CONFIG_PREEMPT_NOTIFIERS in the kernel.
  90  *
  91  * Though I want it to work on older redhat 5 kernels, that have an emulation
  92  * of the feature but not implemented the same way, and instead of linking the
  93  * preempt_notifiers from the task_struct directly, they have a private
  94  * h-table I don't have access to, so I need my own too.
  95  *
  96  * For vanilla kernels we crawl through the task_struct::preempt_notifiers
  97  * hlist until we find our entry, this list is often very short, and it's no
  98  * slower than the global h-table which also crawls a list anyway.
  99  */
 100 #define IS_PRE_2_6_23    (LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 23))
 101
 102 struct pwqr_sb {
 103         struct kref             kref;
 104         struct rcu_head         rcu;
 105         struct timer_list       timer;
 106         wait_queue_head_t       wqh;
 107         wait_queue_head_t       wqh_poll;
 108
 109         unsigned                concurrency;
 110         unsigned                registered;
 111
 112         unsigned                running;
 113         unsigned                waiting;
 114         unsigned                parked;
 115         unsigned                overcommit_wakes;
 116
 117         int                     state;
 118 };
 119
 120 struct pwqr_task {
 121         struct preempt_notifier notifier;
 122         struct pwqr_sb         *sb;
 123         struct rcu_head         rcu;
 124 #if IS_PRE_2_6_23
 125         struct hlist_node       link;
 126         struct task_struct     *task;
 127 #endif
 128 };
 129
 130 #if IS_PRE_2_6_23
 131
 132 #define PWQR_HASH_BITS          5
 133 #define PWQR_HASH_SIZE          (1 << PWQR_HASH_BITS)
 134
 135 struct pwqr_task_bucket {
 136         spinlock_t              lock;
 137         struct hlist_head       tasks;
 138 };
 139
 140 static struct pwqr_task_bucket  pwqr_tasks_hash[PWQR_HASH_SIZE];
 141 #endif
 142
 143 /*
 144  * Global variables
 145  */
 146 static struct class            *pwqr_class;
 147 static int                      pwqr_major;
 148 static struct preempt_ops       pwqr_preempt_running_ops;
 149 static struct preempt_ops       pwqr_preempt_blocked_ops;
 150 static struct preempt_ops       pwqr_preempt_noop_ops;
 151
 152 /*****************************************************************************
 153  * Scoreboards
 154  */
 155
 156 #define pwqr_sb_lock_irqsave(sb, flags) \
 157         spin_lock_irqsave(&(sb)->wqh.lock, flags)
 158 #define pwqr_sb_unlock_irqrestore(sb, flags) \
 159         spin_unlock_irqrestore(&(sb)->wqh.lock, flags)
 160
 161 static inline void pwqr_arm_timer(struct pwqr_sb *sb, int how, int delay)
 162 {
 163         if (timer_pending(&sb->timer) && sb->state == how)
 164                 return;
 165         mod_timer(&sb->timer, jiffies + delay);
 166         sb->state = how;
 167 }
 168
 169 static inline void __pwqr_sb_update_state(struct pwqr_sb *sb, int running_delta)
 170 {
 171         sb->running += running_delta;
 172
 173         if (sb->running < sb->concurrency && sb->waiting == 0 && sb->parked) {
 174                 pwqr_arm_timer(sb, PWQR_STATE_UC, PWQR_UC_DELAY);
 175         } else if (sb->running > sb->concurrency) {
 176                 pwqr_arm_timer(sb, PWQR_STATE_OC, PWQR_OC_DELAY);
 177         } else {
 178                 sb->state = PWQR_STATE_NONE;
 179                 if (!timer_pending(&sb->timer))
 180                         del_timer(&sb->timer);
 181         }
 182 }
 183
 184 static void pwqr_sb_timer_cb(unsigned long arg)
 185 {
 186         struct pwqr_sb *sb = (struct pwqr_sb *)arg;
 187         unsigned long flags;
 188
 189         pwqr_sb_lock_irqsave(sb, flags);
 190         if (sb->running < sb->concurrency && sb->waiting == 0 && sb->parked) {
 191                 if (sb->overcommit_wakes == 0)
 192                         wake_up_locked(&sb->wqh);
 193         }
 194         if (sb->running > sb->concurrency) {
 195                 wake_up_poll(&sb->wqh_poll, POLLIN);
 196         }
 197         pwqr_sb_unlock_irqrestore(sb, flags);
 198 }
 199
 200 static struct pwqr_sb *pwqr_sb_create(void)
 201 {
 202         struct pwqr_sb *sb;
 203
 204         sb = kzalloc(sizeof(struct pwqr_sb), GFP_KERNEL);
 205         if (sb == NULL)
 206                 return ERR_PTR(-ENOMEM);
 207
 208         kref_init(&sb->kref);
 209         init_waitqueue_head(&sb->wqh);
 210         sb->concurrency    = num_online_cpus();
 211         init_timer(&sb->timer);
 212         sb->timer.function = pwqr_sb_timer_cb;
 213         sb->timer.data     = (unsigned long)sb;
 214
 215         __module_get(THIS_MODULE);
 216         return sb;
 217 }
 218 static inline void pwqr_sb_get(struct pwqr_sb *sb)
 219 {
 220         kref_get(&sb->kref);
 221 }
 222
 223 static void pwqr_sb_finalize(struct rcu_head *rcu)
 224 {
 225         struct pwqr_sb *sb = container_of(rcu, struct pwqr_sb, rcu);
 226
 227         module_put(THIS_MODULE);
 228         kfree(sb);
 229 }
 230
 231 static void pwqr_sb_release(struct kref *kref)
 232 {
 233         struct pwqr_sb *sb = container_of(kref, struct pwqr_sb, kref);
 234
 235         del_timer_sync(&sb->timer);
 236         wake_up_poll(&sb->wqh_poll, POLLHUP);
 237         call_rcu(&sb->rcu, pwqr_sb_finalize);
 238 }
 239 static inline void pwqr_sb_put(struct pwqr_sb *sb)
 240 {
 241         kref_put(&sb->kref, pwqr_sb_release);
 242 }
 243
 244 /*****************************************************************************
 245  * tasks
 246  */
 247 #if IS_PRE_2_6_23
 248 static inline struct pwqr_task_bucket *task_hbucket(struct task_struct *task)
 249 {
 250         return &pwqr_tasks_hash[hash_ptr(task, PWQR_HASH_BITS)];
 251 }
 252
 253 static struct pwqr_task *pwqr_task_find(struct task_struct *task)
 254 {
 255         struct pwqr_task_bucket *b = task_hbucket(task);
 256         struct hlist_node *node;
 257         struct pwqr_task *pwqt = NULL;
 258
 259         spin_lock(&b->lock);
 260         hlist_for_each_entry(pwqt, node, &b->tasks, link) {
 261                 if (pwqt->task == task)
 262                         break;
 263         }
 264         spin_unlock(&b->lock);
 265         return pwqt;
 266 }
 267 #else
 268 static struct pwqr_task *pwqr_task_find(struct task_struct *task)
 269 {
 270         struct hlist_node       *node;
 271         struct preempt_notifier *it;
 272         struct pwqr_task        *pwqt = NULL;
 273
 274         hlist_for_each_entry(it, node, &task->preempt_notifiers, link) {
 275                 if (it->ops == &pwqr_preempt_running_ops ||
 276                     it->ops == &pwqr_preempt_blocked_ops ||
 277                     it->ops == &pwqr_preempt_noop_ops)
 278                 {
 279                         pwqt = container_of(it, struct pwqr_task, notifier);
 280                         break;
 281                 }
 282         }
 283
 284         return pwqt;
 285 }
 286 #endif
 287
 288 static struct pwqr_task *pwqr_task_create(struct task_struct *task)
 289 {
 290         struct pwqr_task *pwqt;
 291
 292         pwqt = kmalloc(sizeof(*pwqt), GFP_KERNEL);
 293         if (pwqt == NULL)
 294                 return ERR_PTR(-ENOMEM);
 295
 296         preempt_notifier_init(&pwqt->notifier, &pwqr_preempt_running_ops);
 297         preempt_notifier_register(&pwqt->notifier);
 298 #if IS_PRE_2_6_23
 299         {
 300                 struct pwqr_task_bucket *b = task_hbucket(task);
 301
 302                 pwqt->task = task;
 303                 spin_lock(&b->lock);
 304                 hlist_add_head(&pwqt->link, &b->tasks);
 305                 spin_unlock(&b->lock);
 306         }
 307 #endif
 308         return pwqt;
 309 }
 310
 311 __cold
 312 static void pwqr_task_detach(struct pwqr_task *pwqt, struct pwqr_sb *sb)
 313 {
 314         unsigned long flags;
 315
 316         pwqr_sb_lock_irqsave(sb, flags);
 317         sb->registered--;
 318         if (pwqt->notifier.ops == &pwqr_preempt_running_ops) {
 319                 __pwqr_sb_update_state(sb, -1);
 320         } else {
 321                 __pwqr_sb_update_state(sb, 0);
 322         }
 323         pwqr_sb_unlock_irqrestore(sb, flags);
 324         pwqr_sb_put(sb);
 325         pwqt->sb = NULL;
 326 }
 327
 328 __cold
 329 static void pwqr_task_attach(struct pwqr_task *pwqt, struct pwqr_sb *sb)
 330 {
 331         unsigned long flags;
 332
 333         pwqr_sb_lock_irqsave(sb, flags);
 334         pwqr_sb_get(pwqt->sb = sb);
 335         sb->registered++;
 336         __pwqr_sb_update_state(sb, 1);
 337         pwqr_sb_unlock_irqrestore(sb, flags);
 338 }
 339
 340 __cold
 341 static void pwqr_task_release(struct pwqr_task *pwqt, bool from_notifier)
 342 {
 343 #if IS_PRE_2_6_23
 344         struct pwqr_task_bucket *b = task_hbucket(pwqt->task);
 345
 346         spin_lock(&b->lock);
 347         hlist_del(&pwqt->link);
 348         spin_unlock(&b->lock);
 349 #endif
 350         pwqt->notifier.ops = &pwqr_preempt_noop_ops;
 351
 352         if (from_notifier) {
 353                 /* When called from sched_{out,in}, it's not allowed to
 354                  * call preempt_notifier_unregister (or worse kfree())
 355                  *
 356                  * Though it's not a good idea to kfree() still registered
 357                  * callbacks if we're not dying, it'll panic on the next
 358                  * sched_{in,out} call.
 359                  */
 360                 BUG_ON(!(current->state & TASK_DEAD));
 361                 kfree_rcu(pwqt, rcu);
 362         } else {
 363                 preempt_notifier_unregister(&pwqt->notifier);
 364                 kfree(pwqt);
 365         }
 366 }
 367
 368 static void pwqr_task_noop_sched_in(struct preempt_notifier *notifier, int cpu)
 369 {
 370 }
 371
 372 static void pwqr_task_noop_sched_out(struct preempt_notifier *notifier,
 373                                     struct task_struct *next)
 374 {
 375 }
 376
 377 static void pwqr_task_blocked_sched_in(struct preempt_notifier *notifier, int cpu)
 378 {
 379         struct pwqr_task *pwqt = container_of(notifier, struct pwqr_task, notifier);
 380         struct pwqr_sb   *sb   = pwqt->sb;
 381         unsigned long flags;
 382
 383         if (unlikely(sb->state < 0)) {
 384                 pwqr_task_detach(pwqt, sb);
 385                 pwqr_task_release(pwqt, true);
 386                 return;
 387         }
 388
 389         pwqt->notifier.ops = &pwqr_preempt_running_ops;
 390         pwqr_sb_lock_irqsave(sb, flags);
 391         __pwqr_sb_update_state(sb, 1);
 392         pwqr_sb_unlock_irqrestore(sb, flags);
 393 }
 394
 395 static void pwqr_task_sched_out(struct preempt_notifier *notifier,
 396                                 struct task_struct *next)
 397 {
 398         struct pwqr_task   *pwqt = container_of(notifier, struct pwqr_task, notifier);
 399         struct pwqr_sb     *sb   = pwqt->sb;
 400         struct task_struct *p    = current;
 401
 402         if (unlikely(p->state & TASK_DEAD) || unlikely(sb->state < 0)) {
 403                 pwqr_task_detach(pwqt, sb);
 404                 pwqr_task_release(pwqt, true);
 405                 return;
 406         }
 407         if (p->state == 0 || (p->state & (__TASK_STOPPED | __TASK_TRACED)))
 408                 return;
 409
 410         pwqt->notifier.ops = &pwqr_preempt_blocked_ops;
 411         /* see preempt.h: irq are disabled for sched_out */
 412         spin_lock(&sb->wqh.lock);
 413         __pwqr_sb_update_state(sb, -1);
 414         spin_unlock(&sb->wqh.lock);
 415 }
 416
 417 static struct preempt_ops __read_mostly pwqr_preempt_noop_ops = {
 418         .sched_in       = pwqr_task_noop_sched_in,
 419         .sched_out      = pwqr_task_noop_sched_out,
 420 };
 421
 422 static struct preempt_ops __read_mostly pwqr_preempt_running_ops = {
 423         .sched_in       = pwqr_task_noop_sched_in,
 424         .sched_out      = pwqr_task_sched_out,
 425 };
 426
 427 static struct preempt_ops __read_mostly pwqr_preempt_blocked_ops = {
 428         .sched_in       = pwqr_task_blocked_sched_in,
 429         .sched_out      = pwqr_task_sched_out,
 430 };
 431
 432 /*****************************************************************************
 433  * file descriptor
 434  */
 435 static int pwqr_open(struct inode *inode, struct file *filp)
 436 {
 437         struct pwqr_sb *sb;
 438
 439         sb = pwqr_sb_create();
 440         if (IS_ERR(sb))
 441                 return PTR_ERR(sb);
 442         filp->private_data = sb;
 443         return 0;
 444 }
 445
 446 static int pwqr_release(struct inode *inode, struct file *filp)
 447 {
 448         struct pwqr_sb *sb = filp->private_data;
 449         unsigned long flags;
 450
 451         pwqr_sb_lock_irqsave(sb, flags);
 452         sb->state = PWQR_STATE_DEAD;
 453         pwqr_sb_unlock_irqrestore(sb, flags);
 454         wake_up_all(&sb->wqh);
 455         pwqr_sb_put(sb);
 456         return 0;
 457 }
 458
 459 static unsigned int pwqr_poll(struct file *filp, poll_table *wait)
 460 {
 461         struct pwqr_sb *sb = filp->private_data;
 462         unsigned int events = 0;
 463         unsigned long flags;
 464
 465         poll_wait(filp, &sb->wqh_poll, wait);
 466
 467         pwqr_sb_lock_irqsave(sb, flags);
 468         if (sb->running > sb->concurrency)
 469                 events |= POLLIN;
 470         if (sb->state < 0)
 471                 events |= POLLHUP;
 472         pwqr_sb_unlock_irqrestore(sb, flags);
 473
 474         return events;
 475 }
 476
 477 static inline ssize_t pwqr_sb_read(struct pwqr_sb *sb, int no_wait, u32 *cnt)
 478 {
 479         DECLARE_WAITQUEUE(wait, current);
 480         ssize_t rc = -EAGAIN;
 481
 482         spin_lock_irq(&sb->wqh.lock);
 483         if (sb->running > sb->concurrency) {
 484                 rc = 0;
 485         } else if (!no_wait) {
 486                 add_wait_queue(&sb->wqh_poll, &wait);
 487                 for (;;) {
 488                         set_current_state(TASK_INTERRUPTIBLE);
 489                         if (sb->running > sb->concurrency) {
 490                                 rc = 0;
 491                                 break;
 492                         }
 493                         if (signal_pending(current)) {
 494                                 rc = -ERESTARTSYS;
 495                                 break;
 496                         }
 497                         spin_unlock_irq(&sb->wqh.lock);
 498                         schedule();
 499                         spin_lock_irq(&sb->wqh.lock);
 500                 }
 501                 remove_wait_queue(&sb->wqh_poll, &wait);
 502                 __set_current_state(TASK_RUNNING);
 503         }
 504         if (likely(rc == 0))
 505                 *cnt = sb->running - sb->concurrency;
 506         spin_unlock_irq(&sb->wqh.lock);
 507
 508         return rc;
 509 }
 510
 511 static ssize_t
 512 pwqr_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
 513 {
 514         struct pwqr_sb *sb = filp->private_data;
 515         u32 cnt = 0;
 516         ssize_t rc;
 517
 518         if (count < sizeof(cnt))
 519                 return -EINVAL;
 520         rc = pwqr_sb_read(sb, filp->f_flags & O_NONBLOCK, &cnt);
 521         if (rc < 0)
 522                 return rc;
 523         return put_user(cnt, (u32 __user *)buf) ? -EFAULT : sizeof(cnt);
 524 }
 525
 526 static long
 527 do_pwqr_wait(struct pwqr_sb *sb, struct pwqr_task *pwqt,
 528              int is_wait, struct pwqr_ioc_wait __user *arg)
 529 {
 530         unsigned long flags;
 531         struct pwqr_ioc_wait wait;
 532         long rc = 0;
 533         u32 uval;
 534
 535         preempt_notifier_unregister(&pwqt->notifier);
 536
 537         if (is_wait) {
 538                 if (copy_from_user(&wait, arg, sizeof(wait))) {
 539                         rc = -EFAULT;
 540                         goto out;
 541                 }
 542                 if (unlikely((long)wait.pwqr_uaddr % sizeof(int) != 0)) {
 543                         rc = -EINVAL;
 544                         goto out;
 545                 }
 546         }
 547
 548         pwqr_sb_lock_irqsave(sb, flags);
 549         if (sb->running + sb->waiting <= sb->concurrency) {
 550                 if (is_wait) {
 551                         while (probe_kernel_address(wait.pwqr_uaddr, uval)) {
 552                                 pwqr_sb_unlock_irqrestore(sb, flags);
 553                                 rc = get_user(uval, (u32 *)wait.pwqr_uaddr);
 554                                 if (rc)
 555                                         goto out;
 556                                 pwqr_sb_lock_irqsave(sb, flags);
 557                         }
 558
 559                         if (uval != (u32)wait.pwqr_ticket) {
 560                                 rc = -EWOULDBLOCK;
 561                                 goto out_unlock;
 562                         }
 563                 } else {
 564                         goto out_unlock;
 565                 }
 566         }
 567
 568         /* @ see <wait_event_interruptible_exclusive_locked_irq> */
 569         if (likely(sb->state >= 0)) {
 570                 DEFINE_WAIT(__wait);
 571                 __wait.flags |= WQ_FLAG_EXCLUSIVE;
 572
 573                 if (is_wait) {
 574                         sb->waiting++;
 575                         __add_wait_queue(&sb->wqh, &__wait);
 576                 } else {
 577                         sb->parked++;
 578                         __add_wait_queue_tail(&sb->wqh, &__wait);
 579                 }
 580                 __pwqr_sb_update_state(sb, -1);
 581
 582                 do {
 583                         set_current_state(TASK_INTERRUPTIBLE);
 584                         if (sb->overcommit_wakes)
 585                                 break;
 586                         if (signal_pending(current)) {
 587                                 rc = -ERESTARTSYS;
 588                                 break;
 589                         }
 590                         spin_unlock_irq(&sb->wqh.lock);
 591                         schedule();
 592                         spin_lock_irq(&sb->wqh.lock);
 593                         if (is_wait)
 594                                 break;
 595                         if (sb->running + sb->waiting < sb->concurrency)
 596                                 break;
 597                 } while (likely(sb->state >= 0));
 598
 599                 __remove_wait_queue(&sb->wqh, &__wait);
 600                 __set_current_state(TASK_RUNNING);
 601                 if (is_wait) {
 602                         sb->waiting--;
 603                 } else {
 604                         sb->parked--;
 605                 }
 606                 __pwqr_sb_update_state(sb, 1);
 607
 608                 if (sb->overcommit_wakes)
 609                         sb->overcommit_wakes--;
 610                 if (sb->waiting + sb->running > sb->concurrency)
 611                         rc = -EDQUOT;
 612         }
 613
 614 out_unlock:
 615         if (unlikely(sb->state < 0))
 616                 rc = -EBADFD;
 617         pwqr_sb_unlock_irqrestore(sb, flags);
 618 out:
 619         preempt_notifier_register(&pwqt->notifier);
 620         return rc;
 621 }
 622
 623 static long do_pwqr_unregister(struct pwqr_sb *sb, struct pwqr_task *pwqt)
 624 {
 625         if (!pwqt)
 626                 return -EINVAL;
 627         if (pwqt->sb != sb)
 628                 return -ENOENT;
 629         pwqr_task_detach(pwqt, sb);
 630         pwqr_task_release(pwqt, false);
 631         return 0;
 632 }
 633
 634 static long do_pwqr_set_conc(struct pwqr_sb *sb, int conc)
 635 {
 636         long old_conc = sb->concurrency;
 637         unsigned long flags;
 638
 639         pwqr_sb_lock_irqsave(sb, flags);
 640         if (conc <= 0)
 641                 conc = num_online_cpus();
 642         if (conc != old_conc) {
 643                 sb->concurrency = conc;
 644                 __pwqr_sb_update_state(sb, 0);
 645         }
 646         pwqr_sb_unlock_irqrestore(sb, flags);
 647
 648         return old_conc;
 649 }
 650
 651 static long do_pwqr_wake(struct pwqr_sb *sb, int oc, int count)
 652 {
 653         unsigned long flags;
 654         int nwake;
 655
 656         if (count < 0)
 657                 return -EINVAL;
 658
 659         pwqr_sb_lock_irqsave(sb, flags);
 660
 661         if (oc) {
 662                 nwake = sb->waiting + sb->parked - sb->overcommit_wakes;
 663                 if (count > nwake) {
 664                         count = nwake;
 665                 } else {
 666                         nwake = count;
 667                 }
 668                 sb->overcommit_wakes += count;
 669         } else if (sb->running + sb->overcommit_wakes < sb->concurrency) {
 670                 nwake = sb->concurrency - sb->overcommit_wakes - sb->running;
 671                 if (nwake > sb->waiting + sb->parked - sb->overcommit_wakes) {
 672                         nwake = sb->waiting + sb->parked -
 673                                 sb->overcommit_wakes;
 674                 }
 675                 if (count > nwake) {
 676                         count = nwake;
 677                 } else {
 678                         nwake = count;
 679                 }
 680         } else {
 681                 /*
 682                  * This codepath deserves an explanation: waking the thread
 683                  * "for real" would overcommit, though userspace KNOWS there
 684                  * is at least one waiting thread. Such threads are threads
 685                  * that are "quarantined".
 686                  *
 687                  * Quarantined threads are woken up one by one, to allow a
 688                  * slow ramp down, trying to minimize "waiting" <-> "parked"
 689                  * flip-flops, no matter how many wakes have been asked.
 690                  *
 691                  * Since releasing one quarantined thread will wake up a
 692                  * thread that will (almost) straight go to parked mode, lie
 693                  * to userland about the fact that we unblocked that thread,
 694                  * and return 0.
 695                  *
 696                  * Though if we're already waking all waiting threads for
 697                  * overcommitting jobs, well, we don't need that.
 698                  */
 699                 count = 0;
 700                 nwake = sb->waiting > sb->overcommit_wakes;
 701         }
 702         while (nwake-- > 0)
 703                 wake_up_locked(&sb->wqh);
 704         pwqr_sb_unlock_irqrestore(sb, flags);
 705
 706         return count;
 707 }
 708
 709 static long pwqr_ioctl(struct file *filp, unsigned command, unsigned long arg)
 710 {
 711         struct pwqr_sb     *sb   = filp->private_data;
 712         struct task_struct *task = current;
 713         struct pwqr_task   *pwqt;
 714         int rc = 0;
 715
 716         switch (command) {
 717         case PWQR_CTL_GET_CONC:
 718                 return sb->concurrency;
 719         case PWQR_CTL_SET_CONC:
 720                 return do_pwqr_set_conc(sb, (int)arg);
 721
 722         case PWQR_CTL_WAKE:
 723         case PWQR_CTL_WAKE_OC:
 724                 return do_pwqr_wake(sb, command == PWQR_CTL_WAKE_OC, (int)arg);
 725
 726         case PWQR_CTL_WAIT:
 727         case PWQR_CTL_PARK:
 728         case PWQR_CTL_REGISTER:
 729         case PWQR_CTL_UNREGISTER:
 730                 break;
 731         default:
 732                 return -EINVAL;
 733         }
 734
 735         pwqt = pwqr_task_find(task);
 736         if (command == PWQR_CTL_UNREGISTER)
 737                 return do_pwqr_unregister(sb, pwqt);
 738
 739         if (pwqt == NULL) {
 740                 pwqt = pwqr_task_create(task);
 741                 if (IS_ERR(pwqt))
 742                         return PTR_ERR(pwqt);
 743                 pwqr_task_attach(pwqt, sb);
 744         } else if (unlikely(pwqt->sb != sb)) {
 745                 pwqr_task_detach(pwqt, pwqt->sb);
 746                 pwqr_task_attach(pwqt, sb);
 747         }
 748
 749         switch (command) {
 750         case PWQR_CTL_WAIT:
 751                 rc = do_pwqr_wait(sb, pwqt, true, (struct pwqr_ioc_wait __user *)arg);
 752                 break;
 753         case PWQR_CTL_PARK:
 754                 rc = do_pwqr_wait(sb, pwqt, false, NULL);
 755                 break;
 756         }
 757         return rc;
 758 }
 759
 760 static const struct file_operations pwqr_dev_fops = {
 761         .owner          = THIS_MODULE,
 762         .open           = pwqr_open,
 763         .release        = pwqr_release,
 764         .poll           = pwqr_poll,
 765         .read           = pwqr_read,
 766         .llseek         = noop_llseek,
 767         .unlocked_ioctl = pwqr_ioctl,
 768 #ifdef CONFIG_COMPAT
 769         .compat_ioctl   = pwqr_ioctl,
 770 #endif
 771 };
 772
 773 /*****************************************************************************
 774  * module
 775  */
 776 static int __init pwqr_start(void)
 777 {
 778 #if IS_PRE_2_6_23
 779         int i;
 780
 781         for (i = 0; i < PWQR_HASH_SIZE; i++) {
 782                 spin_lock_init(&pwqr_tasks_hash[i].lock);
 783                 INIT_HLIST_HEAD(&pwqr_tasks_hash[i].tasks);
 784         }
 785 #endif
 786
 787         /* Register as a character device */
 788         pwqr_major = register_chrdev(0, "pwqr", &pwqr_dev_fops);
 789         if (pwqr_major < 0) {
 790                 printk(KERN_ERR "pwqr: register_chrdev() failed\n");
 791                 return pwqr_major;
 792         }
 793
 794         /* Create a device node */
 795         pwqr_class = class_create(THIS_MODULE, PWQR_DEVICE_NAME);
 796         if (IS_ERR(pwqr_class)) {
 797                 printk(KERN_ERR "pwqr: Error creating raw class\n");
 798                 unregister_chrdev(pwqr_major, PWQR_DEVICE_NAME);
 799                 return PTR_ERR(pwqr_class);
 800         }
 801         device_create(pwqr_class, NULL, MKDEV(pwqr_major, 0), NULL, PWQR_DEVICE_NAME);
 802         printk(KERN_INFO "pwqr: PThreads Work Queues Regulator v1 loaded");
 803         return 0;
 804 }
 805
 806 static void __exit pwqr_end(void)
 807 {
 808         rcu_barrier();
 809         device_destroy(pwqr_class, MKDEV(pwqr_major, 0));
 810         class_destroy(pwqr_class);
 811         unregister_chrdev(pwqr_major, PWQR_DEVICE_NAME);
 812 }
 813
 814 module_init(pwqr_start);
 815 module_exit(pwqr_end);
 816
 817 MODULE_LICENSE("GPL");
 818 MODULE_AUTHOR("Pierre Habouzit <pierre.habouzit@intersec.com>");
 819 MODULE_DESCRIPTION("PThreads Work Queues Regulator");
 820 #endif
 821
 822 // vim:noet:sw=8:cinoptions+=\:0,L-1,=1s: