Merge tag 'acpi-3.13-fixup' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael...
[firefly-linux-kernel-4.4.55.git] / include / linux / seqlock.h
1 #ifndef __LINUX_SEQLOCK_H
2 #define __LINUX_SEQLOCK_H
3 /*
4  * Reader/writer consistent mechanism without starving writers. This type of
5  * lock for data where the reader wants a consistent set of information
6  * and is willing to retry if the information changes. There are two types
7  * of readers:
8  * 1. Sequence readers which never block a writer but they may have to retry
9  *    if a writer is in progress by detecting change in sequence number.
10  *    Writers do not wait for a sequence reader.
11  * 2. Locking readers which will wait if a writer or another locking reader
12  *    is in progress. A locking reader in progress will also block a writer
13  *    from going forward. Unlike the regular rwlock, the read lock here is
14  *    exclusive so that only one locking reader can get it.
15  *
16  * This is not as cache friendly as brlock. Also, this may not work well
17  * for data that contains pointers, because any writer could
18  * invalidate a pointer that a reader was following.
19  *
20  * Expected non-blocking reader usage:
21  *      do {
22  *          seq = read_seqbegin(&foo);
23  *      ...
24  *      } while (read_seqretry(&foo, seq));
25  *
26  *
27  * On non-SMP the spin locks disappear but the writer still needs
28  * to increment the sequence variables because an interrupt routine could
29  * change the state of the data.
30  *
31  * Based on x86_64 vsyscall gettimeofday 
32  * by Keith Owens and Andrea Arcangeli
33  */
34
35 #include <linux/spinlock.h>
36 #include <linux/preempt.h>
37 #include <linux/lockdep.h>
38 #include <asm/processor.h>
39
40 /*
41  * Version using sequence counter only.
42  * This can be used when code has its own mutex protecting the
43  * updating starting before the write_seqcountbeqin() and ending
44  * after the write_seqcount_end().
45  */
46 typedef struct seqcount {
47         unsigned sequence;
48 #ifdef CONFIG_DEBUG_LOCK_ALLOC
49         struct lockdep_map dep_map;
50 #endif
51 } seqcount_t;
52
53 static inline void __seqcount_init(seqcount_t *s, const char *name,
54                                           struct lock_class_key *key)
55 {
56         /*
57          * Make sure we are not reinitializing a held lock:
58          */
59         lockdep_init_map(&s->dep_map, name, key, 0);
60         s->sequence = 0;
61 }
62
63 #ifdef CONFIG_DEBUG_LOCK_ALLOC
64 # define SEQCOUNT_DEP_MAP_INIT(lockname) \
65                 .dep_map = { .name = #lockname } \
66
67 # define seqcount_init(s)                               \
68         do {                                            \
69                 static struct lock_class_key __key;     \
70                 __seqcount_init((s), #s, &__key);       \
71         } while (0)
72
73 static inline void seqcount_lockdep_reader_access(const seqcount_t *s)
74 {
75         seqcount_t *l = (seqcount_t *)s;
76         unsigned long flags;
77
78         local_irq_save(flags);
79         seqcount_acquire_read(&l->dep_map, 0, 0, _RET_IP_);
80         seqcount_release(&l->dep_map, 1, _RET_IP_);
81         local_irq_restore(flags);
82 }
83
84 #else
85 # define SEQCOUNT_DEP_MAP_INIT(lockname)
86 # define seqcount_init(s) __seqcount_init(s, NULL, NULL)
87 # define seqcount_lockdep_reader_access(x)
88 #endif
89
90 #define SEQCNT_ZERO(lockname) { .sequence = 0, SEQCOUNT_DEP_MAP_INIT(lockname)}
91
92
93 /**
94  * __read_seqcount_begin - begin a seq-read critical section (without barrier)
95  * @s: pointer to seqcount_t
96  * Returns: count to be passed to read_seqcount_retry
97  *
98  * __read_seqcount_begin is like read_seqcount_begin, but has no smp_rmb()
99  * barrier. Callers should ensure that smp_rmb() or equivalent ordering is
100  * provided before actually loading any of the variables that are to be
101  * protected in this critical section.
102  *
103  * Use carefully, only in critical code, and comment how the barrier is
104  * provided.
105  */
106 static inline unsigned __read_seqcount_begin(const seqcount_t *s)
107 {
108         unsigned ret;
109
110 repeat:
111         ret = ACCESS_ONCE(s->sequence);
112         if (unlikely(ret & 1)) {
113                 cpu_relax();
114                 goto repeat;
115         }
116         return ret;
117 }
118
119 /**
120  * raw_read_seqcount_begin - start seq-read critical section w/o lockdep
121  * @s: pointer to seqcount_t
122  * Returns: count to be passed to read_seqcount_retry
123  *
124  * raw_read_seqcount_begin opens a read critical section of the given
125  * seqcount, but without any lockdep checking. Validity of the critical
126  * section is tested by checking read_seqcount_retry function.
127  */
128 static inline unsigned raw_read_seqcount_begin(const seqcount_t *s)
129 {
130         unsigned ret = __read_seqcount_begin(s);
131         smp_rmb();
132         return ret;
133 }
134
135 /**
136  * read_seqcount_begin - begin a seq-read critical section
137  * @s: pointer to seqcount_t
138  * Returns: count to be passed to read_seqcount_retry
139  *
140  * read_seqcount_begin opens a read critical section of the given seqcount.
141  * Validity of the critical section is tested by checking read_seqcount_retry
142  * function.
143  */
144 static inline unsigned read_seqcount_begin(const seqcount_t *s)
145 {
146         seqcount_lockdep_reader_access(s);
147         return raw_read_seqcount_begin(s);
148 }
149
150 /**
151  * raw_seqcount_begin - begin a seq-read critical section
152  * @s: pointer to seqcount_t
153  * Returns: count to be passed to read_seqcount_retry
154  *
155  * raw_seqcount_begin opens a read critical section of the given seqcount.
156  * Validity of the critical section is tested by checking read_seqcount_retry
157  * function.
158  *
159  * Unlike read_seqcount_begin(), this function will not wait for the count
160  * to stabilize. If a writer is active when we begin, we will fail the
161  * read_seqcount_retry() instead of stabilizing at the beginning of the
162  * critical section.
163  */
164 static inline unsigned raw_seqcount_begin(const seqcount_t *s)
165 {
166         unsigned ret = ACCESS_ONCE(s->sequence);
167
168         seqcount_lockdep_reader_access(s);
169         smp_rmb();
170         return ret & ~1;
171 }
172
173 /**
174  * __read_seqcount_retry - end a seq-read critical section (without barrier)
175  * @s: pointer to seqcount_t
176  * @start: count, from read_seqcount_begin
177  * Returns: 1 if retry is required, else 0
178  *
179  * __read_seqcount_retry is like read_seqcount_retry, but has no smp_rmb()
180  * barrier. Callers should ensure that smp_rmb() or equivalent ordering is
181  * provided before actually loading any of the variables that are to be
182  * protected in this critical section.
183  *
184  * Use carefully, only in critical code, and comment how the barrier is
185  * provided.
186  */
187 static inline int __read_seqcount_retry(const seqcount_t *s, unsigned start)
188 {
189         return unlikely(s->sequence != start);
190 }
191
192 /**
193  * read_seqcount_retry - end a seq-read critical section
194  * @s: pointer to seqcount_t
195  * @start: count, from read_seqcount_begin
196  * Returns: 1 if retry is required, else 0
197  *
198  * read_seqcount_retry closes a read critical section of the given seqcount.
199  * If the critical section was invalid, it must be ignored (and typically
200  * retried).
201  */
202 static inline int read_seqcount_retry(const seqcount_t *s, unsigned start)
203 {
204         smp_rmb();
205         return __read_seqcount_retry(s, start);
206 }
207
208
209
210 static inline void raw_write_seqcount_begin(seqcount_t *s)
211 {
212         s->sequence++;
213         smp_wmb();
214 }
215
216 static inline void raw_write_seqcount_end(seqcount_t *s)
217 {
218         smp_wmb();
219         s->sequence++;
220 }
221
222 /*
223  * Sequence counter only version assumes that callers are using their
224  * own mutexing.
225  */
226 static inline void write_seqcount_begin_nested(seqcount_t *s, int subclass)
227 {
228         raw_write_seqcount_begin(s);
229         seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_);
230 }
231
232 static inline void write_seqcount_begin(seqcount_t *s)
233 {
234         write_seqcount_begin_nested(s, 0);
235 }
236
237 static inline void write_seqcount_end(seqcount_t *s)
238 {
239         seqcount_release(&s->dep_map, 1, _RET_IP_);
240         raw_write_seqcount_end(s);
241 }
242
243 /**
244  * write_seqcount_barrier - invalidate in-progress read-side seq operations
245  * @s: pointer to seqcount_t
246  *
247  * After write_seqcount_barrier, no read-side seq operations will complete
248  * successfully and see data older than this.
249  */
250 static inline void write_seqcount_barrier(seqcount_t *s)
251 {
252         smp_wmb();
253         s->sequence+=2;
254 }
255
256 typedef struct {
257         struct seqcount seqcount;
258         spinlock_t lock;
259 } seqlock_t;
260
261 /*
262  * These macros triggered gcc-3.x compile-time problems.  We think these are
263  * OK now.  Be cautious.
264  */
265 #define __SEQLOCK_UNLOCKED(lockname)                    \
266         {                                               \
267                 .seqcount = SEQCNT_ZERO(lockname),      \
268                 .lock = __SPIN_LOCK_UNLOCKED(lockname)  \
269         }
270
271 #define seqlock_init(x)                                 \
272         do {                                            \
273                 seqcount_init(&(x)->seqcount);          \
274                 spin_lock_init(&(x)->lock);             \
275         } while (0)
276
277 #define DEFINE_SEQLOCK(x) \
278                 seqlock_t x = __SEQLOCK_UNLOCKED(x)
279
280 /*
281  * Read side functions for starting and finalizing a read side section.
282  */
283 static inline unsigned read_seqbegin(const seqlock_t *sl)
284 {
285         return read_seqcount_begin(&sl->seqcount);
286 }
287
288 static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start)
289 {
290         return read_seqcount_retry(&sl->seqcount, start);
291 }
292
293 /*
294  * Lock out other writers and update the count.
295  * Acts like a normal spin_lock/unlock.
296  * Don't need preempt_disable() because that is in the spin_lock already.
297  */
298 static inline void write_seqlock(seqlock_t *sl)
299 {
300         spin_lock(&sl->lock);
301         write_seqcount_begin(&sl->seqcount);
302 }
303
304 static inline void write_sequnlock(seqlock_t *sl)
305 {
306         write_seqcount_end(&sl->seqcount);
307         spin_unlock(&sl->lock);
308 }
309
310 static inline void write_seqlock_bh(seqlock_t *sl)
311 {
312         spin_lock_bh(&sl->lock);
313         write_seqcount_begin(&sl->seqcount);
314 }
315
316 static inline void write_sequnlock_bh(seqlock_t *sl)
317 {
318         write_seqcount_end(&sl->seqcount);
319         spin_unlock_bh(&sl->lock);
320 }
321
322 static inline void write_seqlock_irq(seqlock_t *sl)
323 {
324         spin_lock_irq(&sl->lock);
325         write_seqcount_begin(&sl->seqcount);
326 }
327
328 static inline void write_sequnlock_irq(seqlock_t *sl)
329 {
330         write_seqcount_end(&sl->seqcount);
331         spin_unlock_irq(&sl->lock);
332 }
333
334 static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl)
335 {
336         unsigned long flags;
337
338         spin_lock_irqsave(&sl->lock, flags);
339         write_seqcount_begin(&sl->seqcount);
340         return flags;
341 }
342
343 #define write_seqlock_irqsave(lock, flags)                              \
344         do { flags = __write_seqlock_irqsave(lock); } while (0)
345
346 static inline void
347 write_sequnlock_irqrestore(seqlock_t *sl, unsigned long flags)
348 {
349         write_seqcount_end(&sl->seqcount);
350         spin_unlock_irqrestore(&sl->lock, flags);
351 }
352
353 /*
354  * A locking reader exclusively locks out other writers and locking readers,
355  * but doesn't update the sequence number. Acts like a normal spin_lock/unlock.
356  * Don't need preempt_disable() because that is in the spin_lock already.
357  */
358 static inline void read_seqlock_excl(seqlock_t *sl)
359 {
360         spin_lock(&sl->lock);
361 }
362
363 static inline void read_sequnlock_excl(seqlock_t *sl)
364 {
365         spin_unlock(&sl->lock);
366 }
367
368 /**
369  * read_seqbegin_or_lock - begin a sequence number check or locking block
370  * @lock: sequence lock
371  * @seq : sequence number to be checked
372  *
373  * First try it once optimistically without taking the lock. If that fails,
374  * take the lock. The sequence number is also used as a marker for deciding
375  * whether to be a reader (even) or writer (odd).
376  * N.B. seq must be initialized to an even number to begin with.
377  */
378 static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
379 {
380         if (!(*seq & 1))        /* Even */
381                 *seq = read_seqbegin(lock);
382         else                    /* Odd */
383                 read_seqlock_excl(lock);
384 }
385
386 static inline int need_seqretry(seqlock_t *lock, int seq)
387 {
388         return !(seq & 1) && read_seqretry(lock, seq);
389 }
390
391 static inline void done_seqretry(seqlock_t *lock, int seq)
392 {
393         if (seq & 1)
394                 read_sequnlock_excl(lock);
395 }
396
397 static inline void read_seqlock_excl_bh(seqlock_t *sl)
398 {
399         spin_lock_bh(&sl->lock);
400 }
401
402 static inline void read_sequnlock_excl_bh(seqlock_t *sl)
403 {
404         spin_unlock_bh(&sl->lock);
405 }
406
407 static inline void read_seqlock_excl_irq(seqlock_t *sl)
408 {
409         spin_lock_irq(&sl->lock);
410 }
411
412 static inline void read_sequnlock_excl_irq(seqlock_t *sl)
413 {
414         spin_unlock_irq(&sl->lock);
415 }
416
417 static inline unsigned long __read_seqlock_excl_irqsave(seqlock_t *sl)
418 {
419         unsigned long flags;
420
421         spin_lock_irqsave(&sl->lock, flags);
422         return flags;
423 }
424
425 #define read_seqlock_excl_irqsave(lock, flags)                          \
426         do { flags = __read_seqlock_excl_irqsave(lock); } while (0)
427
428 static inline void
429 read_sequnlock_excl_irqrestore(seqlock_t *sl, unsigned long flags)
430 {
431         spin_unlock_irqrestore(&sl->lock, flags);
432 }
433
434 #endif /* __LINUX_SEQLOCK_H */