linux/fs/btrfs/async-thread.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Copyright (C) 2007 Oracle.  All rights reserved.
   4 * Copyright (C) 2014 Fujitsu.  All rights reserved.
   5 */
   6
   7#include <linux/kthread.h>
   8#include <linux/slab.h>
   9#include <linux/list.h>
  10#include <linux/spinlock.h>
  11#include <linux/freezer.h>
  12#include "async-thread.h"
  13#include "ctree.h"
  14
  15enum {
  16        WORK_DONE_BIT,
  17        WORK_ORDER_DONE_BIT,
  18        WORK_HIGH_PRIO_BIT,
  19};
  20
  21#define NO_THRESHOLD (-1)
  22#define DFT_THRESHOLD (32)
  23
  24struct __btrfs_workqueue {
  25        struct workqueue_struct *normal_wq;
  26
  27        /* File system this workqueue services */
  28        struct btrfs_fs_info *fs_info;
  29
  30        /* List head pointing to ordered work list */
  31        struct list_head ordered_list;
  32
  33        /* Spinlock for ordered_list */
  34        spinlock_t list_lock;
  35
  36        /* Thresholding related variants */
  37        atomic_t pending;
  38
  39        /* Up limit of concurrency workers */
  40        int limit_active;
  41
  42        /* Current number of concurrency workers */
  43        int current_active;
  44
  45        /* Threshold to change current_active */
  46        int thresh;
  47        unsigned int count;
  48        spinlock_t thres_lock;
  49};
  50
  51struct btrfs_workqueue {
  52        struct __btrfs_workqueue *normal;
  53        struct __btrfs_workqueue *high;
  54};
  55
  56struct btrfs_fs_info * __pure btrfs_workqueue_owner(const struct __btrfs_workqueue *wq)
  57{
  58        return wq->fs_info;
  59}
  60
  61struct btrfs_fs_info * __pure btrfs_work_owner(const struct btrfs_work *work)
  62{
  63        return work->wq->fs_info;
  64}
  65
  66bool btrfs_workqueue_normal_congested(const struct btrfs_workqueue *wq)
  67{
  68        /*
  69         * We could compare wq->normal->pending with num_online_cpus()
  70         * to support "thresh == NO_THRESHOLD" case, but it requires
  71         * moving up atomic_inc/dec in thresh_queue/exec_hook. Let's
  72         * postpone it until someone needs the support of that case.
  73         */
  74        if (wq->normal->thresh == NO_THRESHOLD)
  75                return false;
  76
  77        return atomic_read(&wq->normal->pending) > wq->normal->thresh * 2;
  78}
  79
  80static struct __btrfs_workqueue *
  81__btrfs_alloc_workqueue(struct btrfs_fs_info *fs_info, const char *name,
  82                        unsigned int flags, int limit_active, int thresh)
  83{
  84        struct __btrfs_workqueue *ret = kzalloc(sizeof(*ret), GFP_KERNEL);
  85
  86        if (!ret)
  87                return NULL;
  88
  89        ret->fs_info = fs_info;
  90        ret->limit_active = limit_active;
  91        atomic_set(&ret->pending, 0);
  92        if (thresh == 0)
  93                thresh = DFT_THRESHOLD;
  94        /* For low threshold, disabling threshold is a better choice */
  95        if (thresh < DFT_THRESHOLD) {
  96                ret->current_active = limit_active;
  97                ret->thresh = NO_THRESHOLD;
  98        } else {
  99                /*
 100                 * For threshold-able wq, let its concurrency grow on demand.
 101                 * Use minimal max_active at alloc time to reduce resource
 102                 * usage.
 103                 */
 104                ret->current_active = 1;
 105                ret->thresh = thresh;
 106        }
 107
 108        if (flags & WQ_HIGHPRI)
 109                ret->normal_wq = alloc_workqueue("btrfs-%s-high", flags,
 110                                                 ret->current_active, name);
 111        else
 112                ret->normal_wq = alloc_workqueue("btrfs-%s", flags,
 113                                                 ret->current_active, name);
 114        if (!ret->normal_wq) {
 115                kfree(ret);
 116                return NULL;
 117        }
 118
 119        INIT_LIST_HEAD(&ret->ordered_list);
 120        spin_lock_init(&ret->list_lock);
 121        spin_lock_init(&ret->thres_lock);
 122        trace_btrfs_workqueue_alloc(ret, name, flags & WQ_HIGHPRI);
 123        return ret;
 124}
 125
 126static inline void
 127__btrfs_destroy_workqueue(struct __btrfs_workqueue *wq);
 128
 129struct btrfs_workqueue *btrfs_alloc_workqueue(struct btrfs_fs_info *fs_info,
 130                                              const char *name,
 131                                              unsigned int flags,
 132                                              int limit_active,
 133                                              int thresh)
 134{
 135        struct btrfs_workqueue *ret = kzalloc(sizeof(*ret), GFP_KERNEL);
 136
 137        if (!ret)
 138                return NULL;
 139
 140        ret->normal = __btrfs_alloc_workqueue(fs_info, name,
 141                                              flags & ~WQ_HIGHPRI,
 142                                              limit_active, thresh);
 143        if (!ret->normal) {
 144                kfree(ret);
 145                return NULL;
 146        }
 147
 148        if (flags & WQ_HIGHPRI) {
 149                ret->high = __btrfs_alloc_workqueue(fs_info, name, flags,
 150                                                    limit_active, thresh);
 151                if (!ret->high) {
 152                        __btrfs_destroy_workqueue(ret->normal);
 153                        kfree(ret);
 154                        return NULL;
 155                }
 156        }
 157        return ret;
 158}
 159
 160/*
 161 * Hook for threshold which will be called in btrfs_queue_work.
 162 * This hook WILL be called in IRQ handler context,
 163 * so workqueue_set_max_active MUST NOT be called in this hook
 164 */
 165static inline void thresh_queue_hook(struct __btrfs_workqueue *wq)
 166{
 167        if (wq->thresh == NO_THRESHOLD)
 168                return;
 169        atomic_inc(&wq->pending);
 170}
 171
 172/*
 173 * Hook for threshold which will be called before executing the work,
 174 * This hook is called in kthread content.
 175 * So workqueue_set_max_active is called here.
 176 */
 177static inline void thresh_exec_hook(struct __btrfs_workqueue *wq)
 178{
 179        int new_current_active;
 180        long pending;
 181        int need_change = 0;
 182
 183        if (wq->thresh == NO_THRESHOLD)
 184                return;
 185
 186        atomic_dec(&wq->pending);
 187        spin_lock(&wq->thres_lock);
 188        /*
 189         * Use wq->count to limit the calling frequency of
 190         * workqueue_set_max_active.
 191         */
 192        wq->count++;
 193        wq->count %= (wq->thresh / 4);
 194        if (!wq->count)
 195                goto  out;
 196        new_current_active = wq->current_active;
 197
 198        /*
 199         * pending may be changed later, but it's OK since we really
 200         * don't need it so accurate to calculate new_max_active.
 201         */
 202        pending = atomic_read(&wq->pending);
 203        if (pending > wq->thresh)
 204                new_current_active++;
 205        if (pending < wq->thresh / 2)
 206                new_current_active--;
 207        new_current_active = clamp_val(new_current_active, 1, wq->limit_active);
 208        if (new_current_active != wq->current_active)  {
 209                need_change = 1;
 210                wq->current_active = new_current_active;
 211        }
 212out:
 213        spin_unlock(&wq->thres_lock);
 214
 215        if (need_change) {
 216                workqueue_set_max_active(wq->normal_wq, wq->current_active);
 217        }
 218}
 219
 220static void run_ordered_work(struct __btrfs_workqueue *wq,
 221                             struct btrfs_work *self)
 222{
 223        struct list_head *list = &wq->ordered_list;
 224        struct btrfs_work *work;
 225        spinlock_t *lock = &wq->list_lock;
 226        unsigned long flags;
 227        bool free_self = false;
 228
 229        while (1) {
 230                spin_lock_irqsave(lock, flags);
 231                if (list_empty(list))
 232                        break;
 233                work = list_entry(list->next, struct btrfs_work,
 234                                  ordered_list);
 235                if (!test_bit(WORK_DONE_BIT, &work->flags))
 236                        break;
 237
 238                /*
 239                 * we are going to call the ordered done function, but
 240                 * we leave the work item on the list as a barrier so
 241                 * that later work items that are done don't have their
 242                 * functions called before this one returns
 243                 */
 244                if (test_and_set_bit(WORK_ORDER_DONE_BIT, &work->flags))
 245                        break;
 246                trace_btrfs_ordered_sched(work);
 247                spin_unlock_irqrestore(lock, flags);
 248                work->ordered_func(work);
 249
 250                /* now take the lock again and drop our item from the list */
 251                spin_lock_irqsave(lock, flags);
 252                list_del(&work->ordered_list);
 253                spin_unlock_irqrestore(lock, flags);
 254
 255                if (work == self) {
 256                        /*
 257                         * This is the work item that the worker is currently
 258                         * executing.
 259                         *
 260                         * The kernel workqueue code guarantees non-reentrancy
 261                         * of work items. I.e., if a work item with the same
 262                         * address and work function is queued twice, the second
 263                         * execution is blocked until the first one finishes. A
 264                         * work item may be freed and recycled with the same
 265                         * work function; the workqueue code assumes that the
 266                         * original work item cannot depend on the recycled work
 267                         * item in that case (see find_worker_executing_work()).
 268                         *
 269                         * Note that different types of Btrfs work can depend on
 270                         * each other, and one type of work on one Btrfs
 271                         * filesystem may even depend on the same type of work
 272                         * on another Btrfs filesystem via, e.g., a loop device.
 273                         * Therefore, we must not allow the current work item to
 274                         * be recycled until we are really done, otherwise we
 275                         * break the above assumption and can deadlock.
 276                         */
 277                        free_self = true;
 278                } else {
 279                        /*
 280                         * We don't want to call the ordered free functions with
 281                         * the lock held.
 282                         */
 283                        work->ordered_free(work);
 284                        /* NB: work must not be dereferenced past this point. */
 285                        trace_btrfs_all_work_done(wq->fs_info, work);
 286                }
 287        }
 288        spin_unlock_irqrestore(lock, flags);
 289
 290        if (free_self) {
 291                self->ordered_free(self);
 292                /* NB: self must not be dereferenced past this point. */
 293                trace_btrfs_all_work_done(wq->fs_info, self);
 294        }
 295}
 296
 297static void btrfs_work_helper(struct work_struct *normal_work)
 298{
 299        struct btrfs_work *work = container_of(normal_work, struct btrfs_work,
 300                                               normal_work);
 301        struct __btrfs_workqueue *wq;
 302        int need_order = 0;
 303
 304        /*
 305         * We should not touch things inside work in the following cases:
 306         * 1) after work->func() if it has no ordered_free
 307         *    Since the struct is freed in work->func().
 308         * 2) after setting WORK_DONE_BIT
 309         *    The work may be freed in other threads almost instantly.
 310         * So we save the needed things here.
 311         */
 312        if (work->ordered_func)
 313                need_order = 1;
 314        wq = work->wq;
 315
 316        trace_btrfs_work_sched(work);
 317        thresh_exec_hook(wq);
 318        work->func(work);
 319        if (need_order) {
 320                set_bit(WORK_DONE_BIT, &work->flags);
 321                run_ordered_work(wq, work);
 322        } else {
 323                /* NB: work must not be dereferenced past this point. */
 324                trace_btrfs_all_work_done(wq->fs_info, work);
 325        }
 326}
 327
 328void btrfs_init_work(struct btrfs_work *work, btrfs_func_t func,
 329                     btrfs_func_t ordered_func, btrfs_func_t ordered_free)
 330{
 331        work->func = func;
 332        work->ordered_func = ordered_func;
 333        work->ordered_free = ordered_free;
 334        INIT_WORK(&work->normal_work, btrfs_work_helper);
 335        INIT_LIST_HEAD(&work->ordered_list);
 336        work->flags = 0;
 337}
 338
 339static inline void __btrfs_queue_work(struct __btrfs_workqueue *wq,
 340                                      struct btrfs_work *work)
 341{
 342        unsigned long flags;
 343
 344        work->wq = wq;
 345        thresh_queue_hook(wq);
 346        if (work->ordered_func) {
 347                spin_lock_irqsave(&wq->list_lock, flags);
 348                list_add_tail(&work->ordered_list, &wq->ordered_list);
 349                spin_unlock_irqrestore(&wq->list_lock, flags);
 350        }
 351        trace_btrfs_work_queued(work);
 352        queue_work(wq->normal_wq, &work->normal_work);
 353}
 354
 355void btrfs_queue_work(struct btrfs_workqueue *wq,
 356                      struct btrfs_work *work)
 357{
 358        struct __btrfs_workqueue *dest_wq;
 359
 360        if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags) && wq->high)
 361                dest_wq = wq->high;
 362        else
 363                dest_wq = wq->normal;
 364        __btrfs_queue_work(dest_wq, work);
 365}
 366
 367static inline void
 368__btrfs_destroy_workqueue(struct __btrfs_workqueue *wq)
 369{
 370        destroy_workqueue(wq->normal_wq);
 371        trace_btrfs_workqueue_destroy(wq);
 372        kfree(wq);
 373}
 374
 375void btrfs_destroy_workqueue(struct btrfs_workqueue *wq)
 376{
 377        if (!wq)
 378                return;
 379        if (wq->high)
 380                __btrfs_destroy_workqueue(wq->high);
 381        __btrfs_destroy_workqueue(wq->normal);
 382        kfree(wq);
 383}
 384
 385void btrfs_workqueue_set_max(struct btrfs_workqueue *wq, int limit_active)
 386{
 387        if (!wq)
 388                return;
 389        wq->normal->limit_active = limit_active;
 390        if (wq->high)
 391                wq->high->limit_active = limit_active;
 392}
 393
 394void btrfs_set_work_high_priority(struct btrfs_work *work)
 395{
 396        set_bit(WORK_HIGH_PRIO_BIT, &work->flags);
 397}
 398
 399void btrfs_flush_workqueue(struct btrfs_workqueue *wq)
 400{
 401        if (wq->high)
 402                flush_workqueue(wq->high->normal_wq);
 403
 404        flush_workqueue(wq->normal->normal_wq);
 405}
 406
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