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                 printk(KERN_DEBUG "wake up poll");
 196                 wake_up_poll(&sb->wqh_poll, POLLIN);
 197         }
 198         pwqr_sb_unlock_irqrestore(sb, flags);
 199 }
 200
 201 static struct pwqr_sb *pwqr_sb_create(void)
 202 {
 203         struct pwqr_sb *sb;
 204
 205         sb = kzalloc(sizeof(struct pwqr_sb), GFP_KERNEL);
 206         if (sb == NULL)
 207                 return ERR_PTR(-ENOMEM);
 208
 209         kref_init(&sb->kref);
 210         init_waitqueue_head(&sb->wqh);
 211         sb->concurrency    = num_online_cpus();
 212         init_timer(&sb->timer);
 213         sb->timer.function = pwqr_sb_timer_cb;
 214         sb->timer.data     = (unsigned long)sb;
 215
 216         __module_get(THIS_MODULE);
 217         return sb;
 218 }
 219 static inline void pwqr_sb_get(struct pwqr_sb *sb)
 220 {
 221         kref_get(&sb->kref);
 222 }
 223
 224 static void pwqr_sb_finalize(struct rcu_head *rcu)
 225 {
 226         struct pwqr_sb *sb = container_of(rcu, struct pwqr_sb, rcu);
 227
 228         module_put(THIS_MODULE);
 229         kfree(sb);
 230 }
 231
 232 static void pwqr_sb_release(struct kref *kref)
 233 {
 234         struct pwqr_sb *sb = container_of(kref, struct pwqr_sb, kref);
 235
 236         del_timer_sync(&sb->timer);
 237         wake_up_poll(&sb->wqh_poll, POLLHUP);
 238         call_rcu(&sb->rcu, pwqr_sb_finalize);
 239 }
 240 static inline void pwqr_sb_put(struct pwqr_sb *sb)
 241 {
 242         kref_put(&sb->kref, pwqr_sb_release);
 243 }
 244
 245 /*****************************************************************************
 246  * tasks
 247  */
 248 #if IS_PRE_2_6_23
 249 static inline struct pwqr_task_bucket *task_hbucket(struct task_struct *task)
 250 {
 251         return &pwqr_tasks_hash[hash_ptr(task, PWQR_HASH_BITS)];
 252 }
 253
 254 static struct pwqr_task *pwqr_task_find(struct task_struct *task)
 255 {
 256         struct pwqr_task_bucket *b = task_hbucket(task);
 257         struct hlist_node *node;
 258         struct pwqr_task *pwqt = NULL;
 259
 260         spin_lock(&b->lock);
 261         hlist_for_each_entry(pwqt, node, &b->tasks, link) {
 262                 if (pwqt->task == task)
 263                         break;
 264         }
 265         spin_unlock(&b->lock);
 266         return pwqt;
 267 }
 268 #else
 269 static struct pwqr_task *pwqr_task_find(struct task_struct *task)
 270 {
 271         struct hlist_node       *node;
 272         struct preempt_notifier *it;
 273         struct pwqr_task        *pwqt = NULL;
 274
 275         hlist_for_each_entry(it, node, &task->preempt_notifiers, link) {
 276                 if (it->ops == &pwqr_preempt_running_ops ||
 277                     it->ops == &pwqr_preempt_blocked_ops ||
 278                     it->ops == &pwqr_preempt_noop_ops)
 279                 {
 280                         pwqt = container_of(it, struct pwqr_task, notifier);
 281                         break;
 282                 }
 283         }
 284
 285         return pwqt;
 286 }
 287 #endif
 288
 289 static struct pwqr_task *pwqr_task_create(struct task_struct *task)
 290 {
 291         struct pwqr_task *pwqt;
 292
 293         pwqt = kmalloc(sizeof(*pwqt), GFP_KERNEL);
 294         if (pwqt == NULL)
 295                 return ERR_PTR(-ENOMEM);
 296
 297         preempt_notifier_init(&pwqt->notifier, &pwqr_preempt_running_ops);
 298         preempt_notifier_register(&pwqt->notifier);
 299 #if IS_PRE_2_6_23
 300         {
 301                 struct pwqr_task_bucket *b = task_hbucket(task);
 302
 303                 pwqt->task = task;
 304                 spin_lock(&b->lock);
 305                 hlist_add_head(&pwqt->link, &b->tasks);
 306                 spin_unlock(&b->lock);
 307         }
 308 #endif
 309         return pwqt;
 310 }
 311
 312 __cold
 313 static void pwqr_task_detach(struct pwqr_task *pwqt, struct pwqr_sb *sb)
 314 {
 315         unsigned long flags;
 316
 317         pwqr_sb_lock_irqsave(sb, flags);
 318         sb->registered--;
 319         if (pwqt->notifier.ops == &pwqr_preempt_running_ops) {
 320                 __pwqr_sb_update_state(sb, -1);
 321         } else {
 322                 __pwqr_sb_update_state(sb, 0);
 323         }
 324         pwqr_sb_unlock_irqrestore(sb, flags);
 325         pwqr_sb_put(sb);
 326         pwqt->sb = NULL;
 327 }
 328
 329 __cold
 330 static void pwqr_task_attach(struct pwqr_task *pwqt, struct pwqr_sb *sb)
 331 {
 332         unsigned long flags;
 333
 334         pwqr_sb_lock_irqsave(sb, flags);
 335         pwqr_sb_get(pwqt->sb = sb);
 336         sb->registered++;
 337         __pwqr_sb_update_state(sb, 1);
 338         pwqr_sb_unlock_irqrestore(sb, flags);
 339 }
 340
 341 __cold
 342 static void pwqr_task_release(struct pwqr_task *pwqt, bool from_notifier)
 343 {
 344 #if IS_PRE_2_6_23
 345         struct pwqr_task_bucket *b = task_hbucket(pwqt->task);
 346
 347         spin_lock(&b->lock);
 348         hlist_del(&pwqt->link);
 349         spin_unlock(&b->lock);
 350 #endif
 351         pwqt->notifier.ops = &pwqr_preempt_noop_ops;
 352
 353         if (from_notifier) {
 354                 /* When called from sched_{out,in}, it's not allowed to
 355                  * call preempt_notifier_unregister (or worse kfree())
 356                  *
 357                  * Though it's not a good idea to kfree() still registered
 358                  * callbacks if we're not dying, it'll panic on the next
 359                  * sched_{in,out} call.
 360                  */
 361                 BUG_ON(!(current->state & TASK_DEAD));
 362                 kfree_rcu(pwqt, rcu);
 363         } else {
 364                 preempt_notifier_unregister(&pwqt->notifier);
 365                 kfree(pwqt);
 366         }
 367 }
 368
 369 static void pwqr_task_noop_sched_in(struct preempt_notifier *notifier, int cpu)
 370 {
 371 }
 372
 373 static void pwqr_task_noop_sched_out(struct preempt_notifier *notifier,
 374                                     struct task_struct *next)
 375 {
 376 }
 377
 378 static void pwqr_task_blocked_sched_in(struct preempt_notifier *notifier, int cpu)
 379 {
 380         struct pwqr_task *pwqt = container_of(notifier, struct pwqr_task, notifier);
 381         struct pwqr_sb   *sb   = pwqt->sb;
 382         unsigned long flags;
 383
 384         if (unlikely(sb->state < 0)) {
 385                 pwqr_task_detach(pwqt, sb);
 386                 pwqr_task_release(pwqt, true);
 387                 return;
 388         }
 389
 390         pwqt->notifier.ops = &pwqr_preempt_running_ops;
 391         pwqr_sb_lock_irqsave(sb, flags);
 392         __pwqr_sb_update_state(sb, 1);
 393         pwqr_sb_unlock_irqrestore(sb, flags);
 394 }
 395
 396 static void pwqr_task_sched_out(struct preempt_notifier *notifier,
 397                                 struct task_struct *next)
 398 {
 399         struct pwqr_task   *pwqt = container_of(notifier, struct pwqr_task, notifier);
 400         struct pwqr_sb     *sb   = pwqt->sb;
 401         struct task_struct *p    = current;
 402
 403         if (unlikely(p->state & TASK_DEAD) || unlikely(sb->state < 0)) {
 404                 pwqr_task_detach(pwqt, sb);
 405                 pwqr_task_release(pwqt, true);
 406                 return;
 407         }
 408         if (p->state == 0 || (p->state & (__TASK_STOPPED | __TASK_TRACED)))
 409                 return;
 410
 411         pwqt->notifier.ops = &pwqr_preempt_blocked_ops;
 412         /* see preempt.h: irq are disabled for sched_out */
 413         spin_lock(&sb->wqh.lock);
 414         __pwqr_sb_update_state(sb, -1);
 415         spin_unlock(&sb->wqh.lock);
 416 }
 417
 418 static struct preempt_ops __read_mostly pwqr_preempt_noop_ops = {
 419         .sched_in       = pwqr_task_noop_sched_in,
 420         .sched_out      = pwqr_task_noop_sched_out,
 421 };
 422
 423 static struct preempt_ops __read_mostly pwqr_preempt_running_ops = {
 424         .sched_in       = pwqr_task_noop_sched_in,
 425         .sched_out      = pwqr_task_sched_out,
 426 };
 427
 428 static struct preempt_ops __read_mostly pwqr_preempt_blocked_ops = {
 429         .sched_in       = pwqr_task_blocked_sched_in,
 430         .sched_out      = pwqr_task_sched_out,
 431 };
 432
 433 /*****************************************************************************
 434  * file descriptor
 435  */
 436 static int pwqr_open(struct inode *inode, struct file *filp)
 437 {
 438         struct pwqr_sb *sb;
 439
 440         sb = pwqr_sb_create();
 441         if (IS_ERR(sb))
 442                 return PTR_ERR(sb);
 443         filp->private_data = sb;
 444         return 0;
 445 }
 446
 447 static int pwqr_release(struct inode *inode, struct file *filp)
 448 {
 449         struct pwqr_sb *sb = filp->private_data;
 450         unsigned long flags;
 451
 452         pwqr_sb_lock_irqsave(sb, flags);
 453         sb->state = PWQR_STATE_DEAD;
 454         pwqr_sb_unlock_irqrestore(sb, flags);
 455         wake_up_all(&sb->wqh);
 456         pwqr_sb_put(sb);
 457         return 0;
 458 }
 459
 460 static unsigned int pwqr_poll(struct file *filp, poll_table *wait)
 461 {
 462         struct pwqr_sb *sb = filp->private_data;
 463         unsigned int events = 0;
 464         unsigned long flags;
 465
 466         poll_wait(filp, &sb->wqh_poll, wait);
 467
 468         pwqr_sb_lock_irqsave(sb, flags);
 469         if (sb->running > sb->concurrency)
 470                 events |= POLLIN;
 471         if (sb->state < 0)
 472                 events |= POLLHUP;
 473         pwqr_sb_unlock_irqrestore(sb, flags);
 474
 475         return events;
 476 }
 477
 478 static inline ssize_t pwqr_sb_read(struct pwqr_sb *sb, int no_wait, u32 *cnt)
 479 {
 480         DECLARE_WAITQUEUE(wait, current);
 481         ssize_t rc = -EAGAIN;
 482
 483         spin_lock_irq(&sb->wqh.lock);
 484         if (sb->running > sb->concurrency) {
 485                 rc = 0;
 486         } else if (!no_wait) {
 487                 add_wait_queue(&sb->wqh_poll, &wait);
 488                 for (;;) {
 489                         set_current_state(TASK_INTERRUPTIBLE);
 490                         if (sb->running > sb->concurrency) {
 491                                 rc = 0;
 492                                 break;
 493                         }
 494                         if (signal_pending(current)) {
 495                                 rc = -ERESTARTSYS;
 496                                 break;
 497                         }
 498                         spin_unlock_irq(&sb->wqh.lock);
 499                         schedule();
 500                         spin_lock_irq(&sb->wqh.lock);
 501                 }
 502                 remove_wait_queue(&sb->wqh_poll, &wait);
 503                 __set_current_state(TASK_RUNNING);
 504         }
 505         if (likely(rc == 0))
 506                 *cnt = sb->running - sb->concurrency;
 507         spin_unlock_irq(&sb->wqh.lock);
 508
 509         return rc;
 510 }
 511
 512 static ssize_t
 513 pwqr_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
 514 {
 515         struct pwqr_sb *sb = filp->private_data;
 516         u32 cnt = 0;
 517         ssize_t rc;
 518
 519         if (count < sizeof(cnt))
 520                 return -EINVAL;
 521         rc = pwqr_sb_read(sb, filp->f_flags & O_NONBLOCK, &cnt);
 522         if (rc < 0)
 523                 return rc;
 524         return put_user(cnt, (u32 __user *)buf) ? -EFAULT : sizeof(cnt);
 525 }
 526
 527 static long
 528 do_pwqr_wait(struct pwqr_sb *sb, struct pwqr_task *pwqt,
 529              int is_wait, struct pwqr_ioc_wait __user *arg)
 530 {
 531         unsigned long flags;
 532         struct pwqr_ioc_wait wait;
 533         long rc = 0;
 534         u32 uval;
 535
 536         preempt_notifier_unregister(&pwqt->notifier);
 537
 538         if (is_wait) {
 539                 if (copy_from_user(&wait, arg, sizeof(wait))) {
 540                         rc = -EFAULT;
 541                         goto out;
 542                 }
 543                 if (unlikely((long)wait.pwqr_uaddr % sizeof(int) != 0)) {
 544                         rc = -EINVAL;
 545                         goto out;
 546                 }
 547         }
 548
 549         pwqr_sb_lock_irqsave(sb, flags);
 550         if (sb->running + sb->waiting <= sb->concurrency) {
 551                 if (is_wait) {
 552                         while (probe_kernel_address(wait.pwqr_uaddr, uval)) {
 553                                 pwqr_sb_unlock_irqrestore(sb, flags);
 554                                 rc = get_user(uval, (u32 *)wait.pwqr_uaddr);
 555                                 if (rc)
 556                                         goto out;
 557                                 pwqr_sb_lock_irqsave(sb, flags);
 558                         }
 559
 560                         if (uval != (u32)wait.pwqr_ticket) {
 561                                 rc = -EWOULDBLOCK;
 562                                 goto out_unlock;
 563                         }
 564                 } else {
 565                         goto out_unlock;
 566                 }
 567         }
 568
 569         /* @ see <wait_event_interruptible_exclusive_locked_irq> */
 570         if (likely(sb->state >= 0)) {
 571                 DEFINE_WAIT(__wait);
 572                 __wait.flags |= WQ_FLAG_EXCLUSIVE;
 573
 574                 if (is_wait) {
 575                         sb->waiting++;
 576                         __add_wait_queue(&sb->wqh, &__wait);
 577                 } else {
 578                         sb->parked++;
 579                         __add_wait_queue_tail(&sb->wqh, &__wait);
 580                 }
 581                 __pwqr_sb_update_state(sb, -1);
 582
 583                 do {
 584                         set_current_state(TASK_INTERRUPTIBLE);
 585                         if (sb->overcommit_wakes)
 586                                 break;
 587                         if (signal_pending(current)) {
 588                                 rc = -ERESTARTSYS;
 589                                 break;
 590                         }
 591                         spin_unlock_irq(&sb->wqh.lock);
 592                         schedule();
 593                         spin_lock_irq(&sb->wqh.lock);
 594                         if (is_wait)
 595                                 break;
 596                         if (sb->running + sb->waiting < sb->concurrency)
 597                                 break;
 598                 } while (likely(sb->state >= 0));
 599
 600                 __remove_wait_queue(&sb->wqh, &__wait);
 601                 __set_current_state(TASK_RUNNING);
 602                 if (is_wait) {
 603                         sb->waiting--;
 604                 } else {
 605                         sb->parked--;
 606                 }
 607                 __pwqr_sb_update_state(sb, 1);
 608
 609                 if (sb->overcommit_wakes)
 610                         sb->overcommit_wakes--;
 611                 if (sb->waiting + sb->running > sb->concurrency)
 612                         rc = -EDQUOT;
 613         }
 614
 615 out_unlock:
 616         if (unlikely(sb->state < 0))
 617                 rc = -EBADFD;
 618         pwqr_sb_unlock_irqrestore(sb, flags);
 619 out:
 620         preempt_notifier_register(&pwqt->notifier);
 621         return rc;
 622 }
 623
 624 static long do_pwqr_unregister(struct pwqr_sb *sb, struct pwqr_task *pwqt)
 625 {
 626         if (!pwqt)
 627                 return -EINVAL;
 628         if (pwqt->sb != sb)
 629                 return -ENOENT;
 630         pwqr_task_detach(pwqt, sb);
 631         pwqr_task_release(pwqt, false);
 632         return 0;
 633 }
 634
 635 static long do_pwqr_set_conc(struct pwqr_sb *sb, int conc)
 636 {
 637         long old_conc = sb->concurrency;
 638         unsigned long flags;
 639
 640         pwqr_sb_lock_irqsave(sb, flags);
 641         if (conc <= 0)
 642                 conc = num_online_cpus();
 643         if (conc != old_conc) {
 644                 sb->concurrency = conc;
 645                 __pwqr_sb_update_state(sb, 0);
 646         }
 647         pwqr_sb_unlock_irqrestore(sb, flags);
 648
 649         return old_conc;
 650 }
 651
 652 static long do_pwqr_wake(struct pwqr_sb *sb, int oc, int count)
 653 {
 654         unsigned long flags;
 655         int nwake;
 656
 657         if (count < 0)
 658                 return -EINVAL;
 659
 660         pwqr_sb_lock_irqsave(sb, flags);
 661
 662         if (oc) {
 663                 nwake = sb->waiting + sb->parked - sb->overcommit_wakes;
 664                 if (count > nwake) {
 665                         count = nwake;
 666                 } else {
 667                         nwake = count;
 668                 }
 669                 sb->overcommit_wakes += count;
 670         } else if (sb->running + sb->overcommit_wakes < sb->concurrency) {
 671                 nwake = sb->concurrency - sb->overcommit_wakes - sb->running;
 672                 if (nwake > sb->waiting + sb->parked - sb->overcommit_wakes) {
 673                         nwake = sb->waiting + sb->parked -
 674                                 sb->overcommit_wakes;
 675                 }
 676                 if (count > nwake) {
 677                         count = nwake;
 678                 } else {
 679                         nwake = count;
 680                 }
 681         } else {
 682                 /*
 683                  * This codepath deserves an explanation: waking the thread
 684                  * "for real" would overcommit, though userspace KNOWS there
 685                  * is at least one waiting thread. Such threads are threads
 686                  * that are "quarantined".
 687                  *
 688                  * Quarantined threads are woken up one by one, to allow a
 689                  * slow ramp down, trying to minimize "waiting" <-> "parked"
 690                  * flip-flops, no matter how many wakes have been asked.
 691                  *
 692                  * Since releasing one quarantined thread will wake up a
 693                  * thread that will (almost) straight go to parked mode, lie
 694                  * to userland about the fact that we unblocked that thread,
 695                  * and return 0.
 696                  *
 697                  * Though if we're already waking all waiting threads for
 698                  * overcommitting jobs, well, we don't need that.
 699                  */
 700                 count = 0;
 701                 nwake = sb->waiting > sb->overcommit_wakes;
 702         }
 703         while (nwake-- > 0)
 704                 wake_up_locked(&sb->wqh);
 705         pwqr_sb_unlock_irqrestore(sb, flags);
 706
 707         return count;
 708 }
 709
 710 static long pwqr_ioctl(struct file *filp, unsigned command, unsigned long arg)
 711 {
 712         struct pwqr_sb     *sb   = filp->private_data;
 713         struct task_struct *task = current;
 714         struct pwqr_task   *pwqt;
 715         int rc = 0;
 716
 717         switch (command) {
 718         case PWQR_CTL_GET_CONC:
 719                 return sb->concurrency;
 720         case PWQR_CTL_SET_CONC:
 721                 return do_pwqr_set_conc(sb, (int)arg);
 722
 723         case PWQR_CTL_WAKE:
 724         case PWQR_CTL_WAKE_OC:
 725                 return do_pwqr_wake(sb, command == PWQR_CTL_WAKE_OC, (int)arg);
 726
 727         case PWQR_CTL_WAIT:
 728         case PWQR_CTL_PARK:
 729         case PWQR_CTL_REGISTER:
 730         case PWQR_CTL_UNREGISTER:
 731                 break;
 732         default:
 733                 return -EINVAL;
 734         }
 735
 736         pwqt = pwqr_task_find(task);
 737         if (command == PWQR_CTL_UNREGISTER)
 738                 return do_pwqr_unregister(sb, pwqt);
 739
 740         if (pwqt == NULL) {
 741                 pwqt = pwqr_task_create(task);
 742                 if (IS_ERR(pwqt))
 743                         return PTR_ERR(pwqt);
 744                 pwqr_task_attach(pwqt, sb);
 745         } else if (unlikely(pwqt->sb != sb)) {
 746                 pwqr_task_detach(pwqt, pwqt->sb);
 747                 pwqr_task_attach(pwqt, sb);
 748         }
 749
 750         switch (command) {
 751         case PWQR_CTL_WAIT:
 752                 rc = do_pwqr_wait(sb, pwqt, true, (struct pwqr_ioc_wait __user *)arg);
 753                 break;
 754         case PWQR_CTL_PARK:
 755                 rc = do_pwqr_wait(sb, pwqt, false, NULL);
 756                 break;
 757         }
 758         return rc;
 759 }
 760
 761 static const struct file_operations pwqr_dev_fops = {
 762         .owner          = THIS_MODULE,
 763         .open           = pwqr_open,
 764         .release        = pwqr_release,
 765         .poll           = pwqr_poll,
 766         .read           = pwqr_read,
 767         .llseek         = noop_llseek,
 768         .unlocked_ioctl = pwqr_ioctl,
 769 #ifdef CONFIG_COMPAT
 770         .compat_ioctl   = pwqr_ioctl,
 771 #endif
 772 };
 773
 774 /*****************************************************************************
 775  * module
 776  */
 777 static int __init pwqr_start(void)
 778 {
 779 #if IS_PRE_2_6_23
 780         int i;
 781
 782         for (i = 0; i < PWQR_HASH_SIZE; i++) {
 783                 spin_lock_init(&pwqr_tasks_hash[i].lock);
 784                 INIT_HLIST_HEAD(&pwqr_tasks_hash[i].tasks);
 785         }
 786 #endif
 787
 788         /* Register as a character device */
 789         pwqr_major = register_chrdev(0, "pwqr", &pwqr_dev_fops);
 790         if (pwqr_major < 0) {
 791                 printk(KERN_ERR "pwqr: register_chrdev() failed\n");
 792                 return pwqr_major;
 793         }
 794
 795         /* Create a device node */
 796         pwqr_class = class_create(THIS_MODULE, PWQR_DEVICE_NAME);
 797         if (IS_ERR(pwqr_class)) {
 798                 printk(KERN_ERR "pwqr: Error creating raw class\n");
 799                 unregister_chrdev(pwqr_major, PWQR_DEVICE_NAME);
 800                 return PTR_ERR(pwqr_class);
 801         }
 802         device_create(pwqr_class, NULL, MKDEV(pwqr_major, 0), NULL, PWQR_DEVICE_NAME);
 803         printk(KERN_INFO "pwqr: PThreads Work Queues Regulator v1 loaded");
 804         return 0;
 805 }
 806
 807 static void __exit pwqr_end(void)
 808 {
 809         rcu_barrier();
 810         device_destroy(pwqr_class, MKDEV(pwqr_major, 0));
 811         class_destroy(pwqr_class);
 812         unregister_chrdev(pwqr_major, PWQR_DEVICE_NAME);
 813 }
 814
 815 module_init(pwqr_start);
 816 module_exit(pwqr_end);
 817
 818 MODULE_LICENSE("GPL");
 819 MODULE_AUTHOR("Pierre Habouzit <pierre.habouzit@intersec.com>");
 820 MODULE_DESCRIPTION("PThreads Work Queues Regulator");
 821 #endif
 822
 823 // vim:noet:sw=8:cinoptions+=\:0,L-1,=1s: