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