Linux 6.7-rc7
[linux-modified.git] / kernel / locking / rwsem.c
1 // SPDX-License-Identifier: GPL-2.0
2 /* kernel/rwsem.c: R/W semaphores, public implementation
3  *
4  * Written by David Howells (dhowells@redhat.com).
5  * Derived from asm-i386/semaphore.h
6  *
7  * Writer lock-stealing by Alex Shi <alex.shi@intel.com>
8  * and Michel Lespinasse <walken@google.com>
9  *
10  * Optimistic spinning by Tim Chen <tim.c.chen@intel.com>
11  * and Davidlohr Bueso <davidlohr@hp.com>. Based on mutexes.
12  *
13  * Rwsem count bit fields re-definition and rwsem rearchitecture by
14  * Waiman Long <longman@redhat.com> and
15  * Peter Zijlstra <peterz@infradead.org>.
16  */
17
18 #include <linux/types.h>
19 #include <linux/kernel.h>
20 #include <linux/sched.h>
21 #include <linux/sched/rt.h>
22 #include <linux/sched/task.h>
23 #include <linux/sched/debug.h>
24 #include <linux/sched/wake_q.h>
25 #include <linux/sched/signal.h>
26 #include <linux/sched/clock.h>
27 #include <linux/export.h>
28 #include <linux/rwsem.h>
29 #include <linux/atomic.h>
30 #include <trace/events/lock.h>
31
32 #ifndef CONFIG_PREEMPT_RT
33 #include "lock_events.h"
34
35 /*
36  * The least significant 2 bits of the owner value has the following
37  * meanings when set.
38  *  - Bit 0: RWSEM_READER_OWNED - The rwsem is owned by readers
39  *  - Bit 1: RWSEM_NONSPINNABLE - Cannot spin on a reader-owned lock
40  *
41  * When the rwsem is reader-owned and a spinning writer has timed out,
42  * the nonspinnable bit will be set to disable optimistic spinning.
43
44  * When a writer acquires a rwsem, it puts its task_struct pointer
45  * into the owner field. It is cleared after an unlock.
46  *
47  * When a reader acquires a rwsem, it will also puts its task_struct
48  * pointer into the owner field with the RWSEM_READER_OWNED bit set.
49  * On unlock, the owner field will largely be left untouched. So
50  * for a free or reader-owned rwsem, the owner value may contain
51  * information about the last reader that acquires the rwsem.
52  *
53  * That information may be helpful in debugging cases where the system
54  * seems to hang on a reader owned rwsem especially if only one reader
55  * is involved. Ideally we would like to track all the readers that own
56  * a rwsem, but the overhead is simply too big.
57  *
58  * A fast path reader optimistic lock stealing is supported when the rwsem
59  * is previously owned by a writer and the following conditions are met:
60  *  - rwsem is not currently writer owned
61  *  - the handoff isn't set.
62  */
63 #define RWSEM_READER_OWNED      (1UL << 0)
64 #define RWSEM_NONSPINNABLE      (1UL << 1)
65 #define RWSEM_OWNER_FLAGS_MASK  (RWSEM_READER_OWNED | RWSEM_NONSPINNABLE)
66
67 #ifdef CONFIG_DEBUG_RWSEMS
68 # define DEBUG_RWSEMS_WARN_ON(c, sem)   do {                    \
69         if (!debug_locks_silent &&                              \
70             WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, magic = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
71                 #c, atomic_long_read(&(sem)->count),            \
72                 (unsigned long) sem->magic,                     \
73                 atomic_long_read(&(sem)->owner), (long)current, \
74                 list_empty(&(sem)->wait_list) ? "" : "not "))   \
75                         debug_locks_off();                      \
76         } while (0)
77 #else
78 # define DEBUG_RWSEMS_WARN_ON(c, sem)
79 #endif
80
81 /*
82  * On 64-bit architectures, the bit definitions of the count are:
83  *
84  * Bit  0    - writer locked bit
85  * Bit  1    - waiters present bit
86  * Bit  2    - lock handoff bit
87  * Bits 3-7  - reserved
88  * Bits 8-62 - 55-bit reader count
89  * Bit  63   - read fail bit
90  *
91  * On 32-bit architectures, the bit definitions of the count are:
92  *
93  * Bit  0    - writer locked bit
94  * Bit  1    - waiters present bit
95  * Bit  2    - lock handoff bit
96  * Bits 3-7  - reserved
97  * Bits 8-30 - 23-bit reader count
98  * Bit  31   - read fail bit
99  *
100  * It is not likely that the most significant bit (read fail bit) will ever
101  * be set. This guard bit is still checked anyway in the down_read() fastpath
102  * just in case we need to use up more of the reader bits for other purpose
103  * in the future.
104  *
105  * atomic_long_fetch_add() is used to obtain reader lock, whereas
106  * atomic_long_cmpxchg() will be used to obtain writer lock.
107  *
108  * There are three places where the lock handoff bit may be set or cleared.
109  * 1) rwsem_mark_wake() for readers             -- set, clear
110  * 2) rwsem_try_write_lock() for writers        -- set, clear
111  * 3) rwsem_del_waiter()                        -- clear
112  *
113  * For all the above cases, wait_lock will be held. A writer must also
114  * be the first one in the wait_list to be eligible for setting the handoff
115  * bit. So concurrent setting/clearing of handoff bit is not possible.
116  */
117 #define RWSEM_WRITER_LOCKED     (1UL << 0)
118 #define RWSEM_FLAG_WAITERS      (1UL << 1)
119 #define RWSEM_FLAG_HANDOFF      (1UL << 2)
120 #define RWSEM_FLAG_READFAIL     (1UL << (BITS_PER_LONG - 1))
121
122 #define RWSEM_READER_SHIFT      8
123 #define RWSEM_READER_BIAS       (1UL << RWSEM_READER_SHIFT)
124 #define RWSEM_READER_MASK       (~(RWSEM_READER_BIAS - 1))
125 #define RWSEM_WRITER_MASK       RWSEM_WRITER_LOCKED
126 #define RWSEM_LOCK_MASK         (RWSEM_WRITER_MASK|RWSEM_READER_MASK)
127 #define RWSEM_READ_FAILED_MASK  (RWSEM_WRITER_MASK|RWSEM_FLAG_WAITERS|\
128                                  RWSEM_FLAG_HANDOFF|RWSEM_FLAG_READFAIL)
129
130 /*
131  * All writes to owner are protected by WRITE_ONCE() to make sure that
132  * store tearing can't happen as optimistic spinners may read and use
133  * the owner value concurrently without lock. Read from owner, however,
134  * may not need READ_ONCE() as long as the pointer value is only used
135  * for comparison and isn't being dereferenced.
136  *
137  * Both rwsem_{set,clear}_owner() functions should be in the same
138  * preempt disable section as the atomic op that changes sem->count.
139  */
140 static inline void rwsem_set_owner(struct rw_semaphore *sem)
141 {
142         lockdep_assert_preemption_disabled();
143         atomic_long_set(&sem->owner, (long)current);
144 }
145
146 static inline void rwsem_clear_owner(struct rw_semaphore *sem)
147 {
148         lockdep_assert_preemption_disabled();
149         atomic_long_set(&sem->owner, 0);
150 }
151
152 /*
153  * Test the flags in the owner field.
154  */
155 static inline bool rwsem_test_oflags(struct rw_semaphore *sem, long flags)
156 {
157         return atomic_long_read(&sem->owner) & flags;
158 }
159
160 /*
161  * The task_struct pointer of the last owning reader will be left in
162  * the owner field.
163  *
164  * Note that the owner value just indicates the task has owned the rwsem
165  * previously, it may not be the real owner or one of the real owners
166  * anymore when that field is examined, so take it with a grain of salt.
167  *
168  * The reader non-spinnable bit is preserved.
169  */
170 static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
171                                             struct task_struct *owner)
172 {
173         unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED |
174                 (atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE);
175
176         atomic_long_set(&sem->owner, val);
177 }
178
179 static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
180 {
181         __rwsem_set_reader_owned(sem, current);
182 }
183
184 /*
185  * Return true if the rwsem is owned by a reader.
186  */
187 static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
188 {
189 #ifdef CONFIG_DEBUG_RWSEMS
190         /*
191          * Check the count to see if it is write-locked.
192          */
193         long count = atomic_long_read(&sem->count);
194
195         if (count & RWSEM_WRITER_MASK)
196                 return false;
197 #endif
198         return rwsem_test_oflags(sem, RWSEM_READER_OWNED);
199 }
200
201 #ifdef CONFIG_DEBUG_RWSEMS
202 /*
203  * With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there
204  * is a task pointer in owner of a reader-owned rwsem, it will be the
205  * real owner or one of the real owners. The only exception is when the
206  * unlock is done by up_read_non_owner().
207  */
208 static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
209 {
210         unsigned long val = atomic_long_read(&sem->owner);
211
212         while ((val & ~RWSEM_OWNER_FLAGS_MASK) == (unsigned long)current) {
213                 if (atomic_long_try_cmpxchg(&sem->owner, &val,
214                                             val & RWSEM_OWNER_FLAGS_MASK))
215                         return;
216         }
217 }
218 #else
219 static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
220 {
221 }
222 #endif
223
224 /*
225  * Set the RWSEM_NONSPINNABLE bits if the RWSEM_READER_OWNED flag
226  * remains set. Otherwise, the operation will be aborted.
227  */
228 static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
229 {
230         unsigned long owner = atomic_long_read(&sem->owner);
231
232         do {
233                 if (!(owner & RWSEM_READER_OWNED))
234                         break;
235                 if (owner & RWSEM_NONSPINNABLE)
236                         break;
237         } while (!atomic_long_try_cmpxchg(&sem->owner, &owner,
238                                           owner | RWSEM_NONSPINNABLE));
239 }
240
241 static inline bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp)
242 {
243         *cntp = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
244
245         if (WARN_ON_ONCE(*cntp < 0))
246                 rwsem_set_nonspinnable(sem);
247
248         if (!(*cntp & RWSEM_READ_FAILED_MASK)) {
249                 rwsem_set_reader_owned(sem);
250                 return true;
251         }
252
253         return false;
254 }
255
256 static inline bool rwsem_write_trylock(struct rw_semaphore *sem)
257 {
258         long tmp = RWSEM_UNLOCKED_VALUE;
259
260         if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, RWSEM_WRITER_LOCKED)) {
261                 rwsem_set_owner(sem);
262                 return true;
263         }
264
265         return false;
266 }
267
268 /*
269  * Return just the real task structure pointer of the owner
270  */
271 static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
272 {
273         return (struct task_struct *)
274                 (atomic_long_read(&sem->owner) & ~RWSEM_OWNER_FLAGS_MASK);
275 }
276
277 /*
278  * Return the real task structure pointer of the owner and the embedded
279  * flags in the owner. pflags must be non-NULL.
280  */
281 static inline struct task_struct *
282 rwsem_owner_flags(struct rw_semaphore *sem, unsigned long *pflags)
283 {
284         unsigned long owner = atomic_long_read(&sem->owner);
285
286         *pflags = owner & RWSEM_OWNER_FLAGS_MASK;
287         return (struct task_struct *)(owner & ~RWSEM_OWNER_FLAGS_MASK);
288 }
289
290 /*
291  * Guide to the rw_semaphore's count field.
292  *
293  * When the RWSEM_WRITER_LOCKED bit in count is set, the lock is owned
294  * by a writer.
295  *
296  * The lock is owned by readers when
297  * (1) the RWSEM_WRITER_LOCKED isn't set in count,
298  * (2) some of the reader bits are set in count, and
299  * (3) the owner field has RWSEM_READ_OWNED bit set.
300  *
301  * Having some reader bits set is not enough to guarantee a readers owned
302  * lock as the readers may be in the process of backing out from the count
303  * and a writer has just released the lock. So another writer may steal
304  * the lock immediately after that.
305  */
306
307 /*
308  * Initialize an rwsem:
309  */
310 void __init_rwsem(struct rw_semaphore *sem, const char *name,
311                   struct lock_class_key *key)
312 {
313 #ifdef CONFIG_DEBUG_LOCK_ALLOC
314         /*
315          * Make sure we are not reinitializing a held semaphore:
316          */
317         debug_check_no_locks_freed((void *)sem, sizeof(*sem));
318         lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
319 #endif
320 #ifdef CONFIG_DEBUG_RWSEMS
321         sem->magic = sem;
322 #endif
323         atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
324         raw_spin_lock_init(&sem->wait_lock);
325         INIT_LIST_HEAD(&sem->wait_list);
326         atomic_long_set(&sem->owner, 0L);
327 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
328         osq_lock_init(&sem->osq);
329 #endif
330 }
331 EXPORT_SYMBOL(__init_rwsem);
332
333 enum rwsem_waiter_type {
334         RWSEM_WAITING_FOR_WRITE,
335         RWSEM_WAITING_FOR_READ
336 };
337
338 struct rwsem_waiter {
339         struct list_head list;
340         struct task_struct *task;
341         enum rwsem_waiter_type type;
342         unsigned long timeout;
343         bool handoff_set;
344 };
345 #define rwsem_first_waiter(sem) \
346         list_first_entry(&sem->wait_list, struct rwsem_waiter, list)
347
348 enum rwsem_wake_type {
349         RWSEM_WAKE_ANY,         /* Wake whatever's at head of wait list */
350         RWSEM_WAKE_READERS,     /* Wake readers only */
351         RWSEM_WAKE_READ_OWNED   /* Waker thread holds the read lock */
352 };
353
354 /*
355  * The typical HZ value is either 250 or 1000. So set the minimum waiting
356  * time to at least 4ms or 1 jiffy (if it is higher than 4ms) in the wait
357  * queue before initiating the handoff protocol.
358  */
359 #define RWSEM_WAIT_TIMEOUT      DIV_ROUND_UP(HZ, 250)
360
361 /*
362  * Magic number to batch-wakeup waiting readers, even when writers are
363  * also present in the queue. This both limits the amount of work the
364  * waking thread must do and also prevents any potential counter overflow,
365  * however unlikely.
366  */
367 #define MAX_READERS_WAKEUP      0x100
368
369 static inline void
370 rwsem_add_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter)
371 {
372         lockdep_assert_held(&sem->wait_lock);
373         list_add_tail(&waiter->list, &sem->wait_list);
374         /* caller will set RWSEM_FLAG_WAITERS */
375 }
376
377 /*
378  * Remove a waiter from the wait_list and clear flags.
379  *
380  * Both rwsem_mark_wake() and rwsem_try_write_lock() contain a full 'copy' of
381  * this function. Modify with care.
382  *
383  * Return: true if wait_list isn't empty and false otherwise
384  */
385 static inline bool
386 rwsem_del_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter)
387 {
388         lockdep_assert_held(&sem->wait_lock);
389         list_del(&waiter->list);
390         if (likely(!list_empty(&sem->wait_list)))
391                 return true;
392
393         atomic_long_andnot(RWSEM_FLAG_HANDOFF | RWSEM_FLAG_WAITERS, &sem->count);
394         return false;
395 }
396
397 /*
398  * handle the lock release when processes blocked on it that can now run
399  * - if we come here from up_xxxx(), then the RWSEM_FLAG_WAITERS bit must
400  *   have been set.
401  * - there must be someone on the queue
402  * - the wait_lock must be held by the caller
403  * - tasks are marked for wakeup, the caller must later invoke wake_up_q()
404  *   to actually wakeup the blocked task(s) and drop the reference count,
405  *   preferably when the wait_lock is released
406  * - woken process blocks are discarded from the list after having task zeroed
407  * - writers are only marked woken if downgrading is false
408  *
409  * Implies rwsem_del_waiter() for all woken readers.
410  */
411 static void rwsem_mark_wake(struct rw_semaphore *sem,
412                             enum rwsem_wake_type wake_type,
413                             struct wake_q_head *wake_q)
414 {
415         struct rwsem_waiter *waiter, *tmp;
416         long oldcount, woken = 0, adjustment = 0;
417         struct list_head wlist;
418
419         lockdep_assert_held(&sem->wait_lock);
420
421         /*
422          * Take a peek at the queue head waiter such that we can determine
423          * the wakeup(s) to perform.
424          */
425         waiter = rwsem_first_waiter(sem);
426
427         if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
428                 if (wake_type == RWSEM_WAKE_ANY) {
429                         /*
430                          * Mark writer at the front of the queue for wakeup.
431                          * Until the task is actually later awoken later by
432                          * the caller, other writers are able to steal it.
433                          * Readers, on the other hand, will block as they
434                          * will notice the queued writer.
435                          */
436                         wake_q_add(wake_q, waiter->task);
437                         lockevent_inc(rwsem_wake_writer);
438                 }
439
440                 return;
441         }
442
443         /*
444          * No reader wakeup if there are too many of them already.
445          */
446         if (unlikely(atomic_long_read(&sem->count) < 0))
447                 return;
448
449         /*
450          * Writers might steal the lock before we grant it to the next reader.
451          * We prefer to do the first reader grant before counting readers
452          * so we can bail out early if a writer stole the lock.
453          */
454         if (wake_type != RWSEM_WAKE_READ_OWNED) {
455                 struct task_struct *owner;
456
457                 adjustment = RWSEM_READER_BIAS;
458                 oldcount = atomic_long_fetch_add(adjustment, &sem->count);
459                 if (unlikely(oldcount & RWSEM_WRITER_MASK)) {
460                         /*
461                          * When we've been waiting "too" long (for writers
462                          * to give up the lock), request a HANDOFF to
463                          * force the issue.
464                          */
465                         if (time_after(jiffies, waiter->timeout)) {
466                                 if (!(oldcount & RWSEM_FLAG_HANDOFF)) {
467                                         adjustment -= RWSEM_FLAG_HANDOFF;
468                                         lockevent_inc(rwsem_rlock_handoff);
469                                 }
470                                 waiter->handoff_set = true;
471                         }
472
473                         atomic_long_add(-adjustment, &sem->count);
474                         return;
475                 }
476                 /*
477                  * Set it to reader-owned to give spinners an early
478                  * indication that readers now have the lock.
479                  * The reader nonspinnable bit seen at slowpath entry of
480                  * the reader is copied over.
481                  */
482                 owner = waiter->task;
483                 __rwsem_set_reader_owned(sem, owner);
484         }
485
486         /*
487          * Grant up to MAX_READERS_WAKEUP read locks to all the readers in the
488          * queue. We know that the woken will be at least 1 as we accounted
489          * for above. Note we increment the 'active part' of the count by the
490          * number of readers before waking any processes up.
491          *
492          * This is an adaptation of the phase-fair R/W locks where at the
493          * reader phase (first waiter is a reader), all readers are eligible
494          * to acquire the lock at the same time irrespective of their order
495          * in the queue. The writers acquire the lock according to their
496          * order in the queue.
497          *
498          * We have to do wakeup in 2 passes to prevent the possibility that
499          * the reader count may be decremented before it is incremented. It
500          * is because the to-be-woken waiter may not have slept yet. So it
501          * may see waiter->task got cleared, finish its critical section and
502          * do an unlock before the reader count increment.
503          *
504          * 1) Collect the read-waiters in a separate list, count them and
505          *    fully increment the reader count in rwsem.
506          * 2) For each waiters in the new list, clear waiter->task and
507          *    put them into wake_q to be woken up later.
508          */
509         INIT_LIST_HEAD(&wlist);
510         list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {
511                 if (waiter->type == RWSEM_WAITING_FOR_WRITE)
512                         continue;
513
514                 woken++;
515                 list_move_tail(&waiter->list, &wlist);
516
517                 /*
518                  * Limit # of readers that can be woken up per wakeup call.
519                  */
520                 if (unlikely(woken >= MAX_READERS_WAKEUP))
521                         break;
522         }
523
524         adjustment = woken * RWSEM_READER_BIAS - adjustment;
525         lockevent_cond_inc(rwsem_wake_reader, woken);
526
527         oldcount = atomic_long_read(&sem->count);
528         if (list_empty(&sem->wait_list)) {
529                 /*
530                  * Combined with list_move_tail() above, this implies
531                  * rwsem_del_waiter().
532                  */
533                 adjustment -= RWSEM_FLAG_WAITERS;
534                 if (oldcount & RWSEM_FLAG_HANDOFF)
535                         adjustment -= RWSEM_FLAG_HANDOFF;
536         } else if (woken) {
537                 /*
538                  * When we've woken a reader, we no longer need to force
539                  * writers to give up the lock and we can clear HANDOFF.
540                  */
541                 if (oldcount & RWSEM_FLAG_HANDOFF)
542                         adjustment -= RWSEM_FLAG_HANDOFF;
543         }
544
545         if (adjustment)
546                 atomic_long_add(adjustment, &sem->count);
547
548         /* 2nd pass */
549         list_for_each_entry_safe(waiter, tmp, &wlist, list) {
550                 struct task_struct *tsk;
551
552                 tsk = waiter->task;
553                 get_task_struct(tsk);
554
555                 /*
556                  * Ensure calling get_task_struct() before setting the reader
557                  * waiter to nil such that rwsem_down_read_slowpath() cannot
558                  * race with do_exit() by always holding a reference count
559                  * to the task to wakeup.
560                  */
561                 smp_store_release(&waiter->task, NULL);
562                 /*
563                  * Ensure issuing the wakeup (either by us or someone else)
564                  * after setting the reader waiter to nil.
565                  */
566                 wake_q_add_safe(wake_q, tsk);
567         }
568 }
569
570 /*
571  * Remove a waiter and try to wake up other waiters in the wait queue
572  * This function is called from the out_nolock path of both the reader and
573  * writer slowpaths with wait_lock held. It releases the wait_lock and
574  * optionally wake up waiters before it returns.
575  */
576 static inline void
577 rwsem_del_wake_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter,
578                       struct wake_q_head *wake_q)
579                       __releases(&sem->wait_lock)
580 {
581         bool first = rwsem_first_waiter(sem) == waiter;
582
583         wake_q_init(wake_q);
584
585         /*
586          * If the wait_list isn't empty and the waiter to be deleted is
587          * the first waiter, we wake up the remaining waiters as they may
588          * be eligible to acquire or spin on the lock.
589          */
590         if (rwsem_del_waiter(sem, waiter) && first)
591                 rwsem_mark_wake(sem, RWSEM_WAKE_ANY, wake_q);
592         raw_spin_unlock_irq(&sem->wait_lock);
593         if (!wake_q_empty(wake_q))
594                 wake_up_q(wake_q);
595 }
596
597 /*
598  * This function must be called with the sem->wait_lock held to prevent
599  * race conditions between checking the rwsem wait list and setting the
600  * sem->count accordingly.
601  *
602  * Implies rwsem_del_waiter() on success.
603  */
604 static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
605                                         struct rwsem_waiter *waiter)
606 {
607         struct rwsem_waiter *first = rwsem_first_waiter(sem);
608         long count, new;
609
610         lockdep_assert_held(&sem->wait_lock);
611
612         count = atomic_long_read(&sem->count);
613         do {
614                 bool has_handoff = !!(count & RWSEM_FLAG_HANDOFF);
615
616                 if (has_handoff) {
617                         /*
618                          * Honor handoff bit and yield only when the first
619                          * waiter is the one that set it. Otherwisee, we
620                          * still try to acquire the rwsem.
621                          */
622                         if (first->handoff_set && (waiter != first))
623                                 return false;
624                 }
625
626                 new = count;
627
628                 if (count & RWSEM_LOCK_MASK) {
629                         /*
630                          * A waiter (first or not) can set the handoff bit
631                          * if it is an RT task or wait in the wait queue
632                          * for too long.
633                          */
634                         if (has_handoff || (!rt_task(waiter->task) &&
635                                             !time_after(jiffies, waiter->timeout)))
636                                 return false;
637
638                         new |= RWSEM_FLAG_HANDOFF;
639                 } else {
640                         new |= RWSEM_WRITER_LOCKED;
641                         new &= ~RWSEM_FLAG_HANDOFF;
642
643                         if (list_is_singular(&sem->wait_list))
644                                 new &= ~RWSEM_FLAG_WAITERS;
645                 }
646         } while (!atomic_long_try_cmpxchg_acquire(&sem->count, &count, new));
647
648         /*
649          * We have either acquired the lock with handoff bit cleared or set
650          * the handoff bit. Only the first waiter can have its handoff_set
651          * set here to enable optimistic spinning in slowpath loop.
652          */
653         if (new & RWSEM_FLAG_HANDOFF) {
654                 first->handoff_set = true;
655                 lockevent_inc(rwsem_wlock_handoff);
656                 return false;
657         }
658
659         /*
660          * Have rwsem_try_write_lock() fully imply rwsem_del_waiter() on
661          * success.
662          */
663         list_del(&waiter->list);
664         rwsem_set_owner(sem);
665         return true;
666 }
667
668 /*
669  * The rwsem_spin_on_owner() function returns the following 4 values
670  * depending on the lock owner state.
671  *   OWNER_NULL  : owner is currently NULL
672  *   OWNER_WRITER: when owner changes and is a writer
673  *   OWNER_READER: when owner changes and the new owner may be a reader.
674  *   OWNER_NONSPINNABLE:
675  *                 when optimistic spinning has to stop because either the
676  *                 owner stops running, is unknown, or its timeslice has
677  *                 been used up.
678  */
679 enum owner_state {
680         OWNER_NULL              = 1 << 0,
681         OWNER_WRITER            = 1 << 1,
682         OWNER_READER            = 1 << 2,
683         OWNER_NONSPINNABLE      = 1 << 3,
684 };
685
686 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
687 /*
688  * Try to acquire write lock before the writer has been put on wait queue.
689  */
690 static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
691 {
692         long count = atomic_long_read(&sem->count);
693
694         while (!(count & (RWSEM_LOCK_MASK|RWSEM_FLAG_HANDOFF))) {
695                 if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
696                                         count | RWSEM_WRITER_LOCKED)) {
697                         rwsem_set_owner(sem);
698                         lockevent_inc(rwsem_opt_lock);
699                         return true;
700                 }
701         }
702         return false;
703 }
704
705 static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
706 {
707         struct task_struct *owner;
708         unsigned long flags;
709         bool ret = true;
710
711         if (need_resched()) {
712                 lockevent_inc(rwsem_opt_fail);
713                 return false;
714         }
715
716         /*
717          * Disable preemption is equal to the RCU read-side crital section,
718          * thus the task_strcut structure won't go away.
719          */
720         owner = rwsem_owner_flags(sem, &flags);
721         /*
722          * Don't check the read-owner as the entry may be stale.
723          */
724         if ((flags & RWSEM_NONSPINNABLE) ||
725             (owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner)))
726                 ret = false;
727
728         lockevent_cond_inc(rwsem_opt_fail, !ret);
729         return ret;
730 }
731
732 #define OWNER_SPINNABLE         (OWNER_NULL | OWNER_WRITER | OWNER_READER)
733
734 static inline enum owner_state
735 rwsem_owner_state(struct task_struct *owner, unsigned long flags)
736 {
737         if (flags & RWSEM_NONSPINNABLE)
738                 return OWNER_NONSPINNABLE;
739
740         if (flags & RWSEM_READER_OWNED)
741                 return OWNER_READER;
742
743         return owner ? OWNER_WRITER : OWNER_NULL;
744 }
745
746 static noinline enum owner_state
747 rwsem_spin_on_owner(struct rw_semaphore *sem)
748 {
749         struct task_struct *new, *owner;
750         unsigned long flags, new_flags;
751         enum owner_state state;
752
753         lockdep_assert_preemption_disabled();
754
755         owner = rwsem_owner_flags(sem, &flags);
756         state = rwsem_owner_state(owner, flags);
757         if (state != OWNER_WRITER)
758                 return state;
759
760         for (;;) {
761                 /*
762                  * When a waiting writer set the handoff flag, it may spin
763                  * on the owner as well. Once that writer acquires the lock,
764                  * we can spin on it. So we don't need to quit even when the
765                  * handoff bit is set.
766                  */
767                 new = rwsem_owner_flags(sem, &new_flags);
768                 if ((new != owner) || (new_flags != flags)) {
769                         state = rwsem_owner_state(new, new_flags);
770                         break;
771                 }
772
773                 /*
774                  * Ensure we emit the owner->on_cpu, dereference _after_
775                  * checking sem->owner still matches owner, if that fails,
776                  * owner might point to free()d memory, if it still matches,
777                  * our spinning context already disabled preemption which is
778                  * equal to RCU read-side crital section ensures the memory
779                  * stays valid.
780                  */
781                 barrier();
782
783                 if (need_resched() || !owner_on_cpu(owner)) {
784                         state = OWNER_NONSPINNABLE;
785                         break;
786                 }
787
788                 cpu_relax();
789         }
790
791         return state;
792 }
793
794 /*
795  * Calculate reader-owned rwsem spinning threshold for writer
796  *
797  * The more readers own the rwsem, the longer it will take for them to
798  * wind down and free the rwsem. So the empirical formula used to
799  * determine the actual spinning time limit here is:
800  *
801  *   Spinning threshold = (10 + nr_readers/2)us
802  *
803  * The limit is capped to a maximum of 25us (30 readers). This is just
804  * a heuristic and is subjected to change in the future.
805  */
806 static inline u64 rwsem_rspin_threshold(struct rw_semaphore *sem)
807 {
808         long count = atomic_long_read(&sem->count);
809         int readers = count >> RWSEM_READER_SHIFT;
810         u64 delta;
811
812         if (readers > 30)
813                 readers = 30;
814         delta = (20 + readers) * NSEC_PER_USEC / 2;
815
816         return sched_clock() + delta;
817 }
818
819 static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
820 {
821         bool taken = false;
822         int prev_owner_state = OWNER_NULL;
823         int loop = 0;
824         u64 rspin_threshold = 0;
825
826         /* sem->wait_lock should not be held when doing optimistic spinning */
827         if (!osq_lock(&sem->osq))
828                 goto done;
829
830         /*
831          * Optimistically spin on the owner field and attempt to acquire the
832          * lock whenever the owner changes. Spinning will be stopped when:
833          *  1) the owning writer isn't running; or
834          *  2) readers own the lock and spinning time has exceeded limit.
835          */
836         for (;;) {
837                 enum owner_state owner_state;
838
839                 owner_state = rwsem_spin_on_owner(sem);
840                 if (!(owner_state & OWNER_SPINNABLE))
841                         break;
842
843                 /*
844                  * Try to acquire the lock
845                  */
846                 taken = rwsem_try_write_lock_unqueued(sem);
847
848                 if (taken)
849                         break;
850
851                 /*
852                  * Time-based reader-owned rwsem optimistic spinning
853                  */
854                 if (owner_state == OWNER_READER) {
855                         /*
856                          * Re-initialize rspin_threshold every time when
857                          * the owner state changes from non-reader to reader.
858                          * This allows a writer to steal the lock in between
859                          * 2 reader phases and have the threshold reset at
860                          * the beginning of the 2nd reader phase.
861                          */
862                         if (prev_owner_state != OWNER_READER) {
863                                 if (rwsem_test_oflags(sem, RWSEM_NONSPINNABLE))
864                                         break;
865                                 rspin_threshold = rwsem_rspin_threshold(sem);
866                                 loop = 0;
867                         }
868
869                         /*
870                          * Check time threshold once every 16 iterations to
871                          * avoid calling sched_clock() too frequently so
872                          * as to reduce the average latency between the times
873                          * when the lock becomes free and when the spinner
874                          * is ready to do a trylock.
875                          */
876                         else if (!(++loop & 0xf) && (sched_clock() > rspin_threshold)) {
877                                 rwsem_set_nonspinnable(sem);
878                                 lockevent_inc(rwsem_opt_nospin);
879                                 break;
880                         }
881                 }
882
883                 /*
884                  * An RT task cannot do optimistic spinning if it cannot
885                  * be sure the lock holder is running or live-lock may
886                  * happen if the current task and the lock holder happen
887                  * to run in the same CPU. However, aborting optimistic
888                  * spinning while a NULL owner is detected may miss some
889                  * opportunity where spinning can continue without causing
890                  * problem.
891                  *
892                  * There are 2 possible cases where an RT task may be able
893                  * to continue spinning.
894                  *
895                  * 1) The lock owner is in the process of releasing the
896                  *    lock, sem->owner is cleared but the lock has not
897                  *    been released yet.
898                  * 2) The lock was free and owner cleared, but another
899                  *    task just comes in and acquire the lock before
900                  *    we try to get it. The new owner may be a spinnable
901                  *    writer.
902                  *
903                  * To take advantage of two scenarios listed above, the RT
904                  * task is made to retry one more time to see if it can
905                  * acquire the lock or continue spinning on the new owning
906                  * writer. Of course, if the time lag is long enough or the
907                  * new owner is not a writer or spinnable, the RT task will
908                  * quit spinning.
909                  *
910                  * If the owner is a writer, the need_resched() check is
911                  * done inside rwsem_spin_on_owner(). If the owner is not
912                  * a writer, need_resched() check needs to be done here.
913                  */
914                 if (owner_state != OWNER_WRITER) {
915                         if (need_resched())
916                                 break;
917                         if (rt_task(current) &&
918                            (prev_owner_state != OWNER_WRITER))
919                                 break;
920                 }
921                 prev_owner_state = owner_state;
922
923                 /*
924                  * The cpu_relax() call is a compiler barrier which forces
925                  * everything in this loop to be re-loaded. We don't need
926                  * memory barriers as we'll eventually observe the right
927                  * values at the cost of a few extra spins.
928                  */
929                 cpu_relax();
930         }
931         osq_unlock(&sem->osq);
932 done:
933         lockevent_cond_inc(rwsem_opt_fail, !taken);
934         return taken;
935 }
936
937 /*
938  * Clear the owner's RWSEM_NONSPINNABLE bit if it is set. This should
939  * only be called when the reader count reaches 0.
940  */
941 static inline void clear_nonspinnable(struct rw_semaphore *sem)
942 {
943         if (unlikely(rwsem_test_oflags(sem, RWSEM_NONSPINNABLE)))
944                 atomic_long_andnot(RWSEM_NONSPINNABLE, &sem->owner);
945 }
946
947 #else
948 static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
949 {
950         return false;
951 }
952
953 static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem)
954 {
955         return false;
956 }
957
958 static inline void clear_nonspinnable(struct rw_semaphore *sem) { }
959
960 static inline enum owner_state
961 rwsem_spin_on_owner(struct rw_semaphore *sem)
962 {
963         return OWNER_NONSPINNABLE;
964 }
965 #endif
966
967 /*
968  * Prepare to wake up waiter(s) in the wait queue by putting them into the
969  * given wake_q if the rwsem lock owner isn't a writer. If rwsem is likely
970  * reader-owned, wake up read lock waiters in queue front or wake up any
971  * front waiter otherwise.
972
973  * This is being called from both reader and writer slow paths.
974  */
975 static inline void rwsem_cond_wake_waiter(struct rw_semaphore *sem, long count,
976                                           struct wake_q_head *wake_q)
977 {
978         enum rwsem_wake_type wake_type;
979
980         if (count & RWSEM_WRITER_MASK)
981                 return;
982
983         if (count & RWSEM_READER_MASK) {
984                 wake_type = RWSEM_WAKE_READERS;
985         } else {
986                 wake_type = RWSEM_WAKE_ANY;
987                 clear_nonspinnable(sem);
988         }
989         rwsem_mark_wake(sem, wake_type, wake_q);
990 }
991
992 /*
993  * Wait for the read lock to be granted
994  */
995 static struct rw_semaphore __sched *
996 rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int state)
997 {
998         long adjustment = -RWSEM_READER_BIAS;
999         long rcnt = (count >> RWSEM_READER_SHIFT);
1000         struct rwsem_waiter waiter;
1001         DEFINE_WAKE_Q(wake_q);
1002
1003         /*
1004          * To prevent a constant stream of readers from starving a sleeping
1005          * waiter, don't attempt optimistic lock stealing if the lock is
1006          * currently owned by readers.
1007          */
1008         if ((atomic_long_read(&sem->owner) & RWSEM_READER_OWNED) &&
1009             (rcnt > 1) && !(count & RWSEM_WRITER_LOCKED))
1010                 goto queue;
1011
1012         /*
1013          * Reader optimistic lock stealing.
1014          */
1015         if (!(count & (RWSEM_WRITER_LOCKED | RWSEM_FLAG_HANDOFF))) {
1016                 rwsem_set_reader_owned(sem);
1017                 lockevent_inc(rwsem_rlock_steal);
1018
1019                 /*
1020                  * Wake up other readers in the wait queue if it is
1021                  * the first reader.
1022                  */
1023                 if ((rcnt == 1) && (count & RWSEM_FLAG_WAITERS)) {
1024                         raw_spin_lock_irq(&sem->wait_lock);
1025                         if (!list_empty(&sem->wait_list))
1026                                 rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED,
1027                                                 &wake_q);
1028                         raw_spin_unlock_irq(&sem->wait_lock);
1029                         wake_up_q(&wake_q);
1030                 }
1031                 return sem;
1032         }
1033
1034 queue:
1035         waiter.task = current;
1036         waiter.type = RWSEM_WAITING_FOR_READ;
1037         waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
1038         waiter.handoff_set = false;
1039
1040         raw_spin_lock_irq(&sem->wait_lock);
1041         if (list_empty(&sem->wait_list)) {
1042                 /*
1043                  * In case the wait queue is empty and the lock isn't owned
1044                  * by a writer, this reader can exit the slowpath and return
1045                  * immediately as its RWSEM_READER_BIAS has already been set
1046                  * in the count.
1047                  */
1048                 if (!(atomic_long_read(&sem->count) & RWSEM_WRITER_MASK)) {
1049                         /* Provide lock ACQUIRE */
1050                         smp_acquire__after_ctrl_dep();
1051                         raw_spin_unlock_irq(&sem->wait_lock);
1052                         rwsem_set_reader_owned(sem);
1053                         lockevent_inc(rwsem_rlock_fast);
1054                         return sem;
1055                 }
1056                 adjustment += RWSEM_FLAG_WAITERS;
1057         }
1058         rwsem_add_waiter(sem, &waiter);
1059
1060         /* we're now waiting on the lock, but no longer actively locking */
1061         count = atomic_long_add_return(adjustment, &sem->count);
1062
1063         rwsem_cond_wake_waiter(sem, count, &wake_q);
1064         raw_spin_unlock_irq(&sem->wait_lock);
1065
1066         if (!wake_q_empty(&wake_q))
1067                 wake_up_q(&wake_q);
1068
1069         trace_contention_begin(sem, LCB_F_READ);
1070
1071         /* wait to be given the lock */
1072         for (;;) {
1073                 set_current_state(state);
1074                 if (!smp_load_acquire(&waiter.task)) {
1075                         /* Matches rwsem_mark_wake()'s smp_store_release(). */
1076                         break;
1077                 }
1078                 if (signal_pending_state(state, current)) {
1079                         raw_spin_lock_irq(&sem->wait_lock);
1080                         if (waiter.task)
1081                                 goto out_nolock;
1082                         raw_spin_unlock_irq(&sem->wait_lock);
1083                         /* Ordered by sem->wait_lock against rwsem_mark_wake(). */
1084                         break;
1085                 }
1086                 schedule_preempt_disabled();
1087                 lockevent_inc(rwsem_sleep_reader);
1088         }
1089
1090         __set_current_state(TASK_RUNNING);
1091         lockevent_inc(rwsem_rlock);
1092         trace_contention_end(sem, 0);
1093         return sem;
1094
1095 out_nolock:
1096         rwsem_del_wake_waiter(sem, &waiter, &wake_q);
1097         __set_current_state(TASK_RUNNING);
1098         lockevent_inc(rwsem_rlock_fail);
1099         trace_contention_end(sem, -EINTR);
1100         return ERR_PTR(-EINTR);
1101 }
1102
1103 /*
1104  * Wait until we successfully acquire the write lock
1105  */
1106 static struct rw_semaphore __sched *
1107 rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
1108 {
1109         struct rwsem_waiter waiter;
1110         DEFINE_WAKE_Q(wake_q);
1111
1112         /* do optimistic spinning and steal lock if possible */
1113         if (rwsem_can_spin_on_owner(sem) && rwsem_optimistic_spin(sem)) {
1114                 /* rwsem_optimistic_spin() implies ACQUIRE on success */
1115                 return sem;
1116         }
1117
1118         /*
1119          * Optimistic spinning failed, proceed to the slowpath
1120          * and block until we can acquire the sem.
1121          */
1122         waiter.task = current;
1123         waiter.type = RWSEM_WAITING_FOR_WRITE;
1124         waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
1125         waiter.handoff_set = false;
1126
1127         raw_spin_lock_irq(&sem->wait_lock);
1128         rwsem_add_waiter(sem, &waiter);
1129
1130         /* we're now waiting on the lock */
1131         if (rwsem_first_waiter(sem) != &waiter) {
1132                 rwsem_cond_wake_waiter(sem, atomic_long_read(&sem->count),
1133                                        &wake_q);
1134                 if (!wake_q_empty(&wake_q)) {
1135                         /*
1136                          * We want to minimize wait_lock hold time especially
1137                          * when a large number of readers are to be woken up.
1138                          */
1139                         raw_spin_unlock_irq(&sem->wait_lock);
1140                         wake_up_q(&wake_q);
1141                         raw_spin_lock_irq(&sem->wait_lock);
1142                 }
1143         } else {
1144                 atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count);
1145         }
1146
1147         /* wait until we successfully acquire the lock */
1148         set_current_state(state);
1149         trace_contention_begin(sem, LCB_F_WRITE);
1150
1151         for (;;) {
1152                 if (rwsem_try_write_lock(sem, &waiter)) {
1153                         /* rwsem_try_write_lock() implies ACQUIRE on success */
1154                         break;
1155                 }
1156
1157                 raw_spin_unlock_irq(&sem->wait_lock);
1158
1159                 if (signal_pending_state(state, current))
1160                         goto out_nolock;
1161
1162                 /*
1163                  * After setting the handoff bit and failing to acquire
1164                  * the lock, attempt to spin on owner to accelerate lock
1165                  * transfer. If the previous owner is a on-cpu writer and it
1166                  * has just released the lock, OWNER_NULL will be returned.
1167                  * In this case, we attempt to acquire the lock again
1168                  * without sleeping.
1169                  */
1170                 if (waiter.handoff_set) {
1171                         enum owner_state owner_state;
1172
1173                         owner_state = rwsem_spin_on_owner(sem);
1174                         if (owner_state == OWNER_NULL)
1175                                 goto trylock_again;
1176                 }
1177
1178                 schedule_preempt_disabled();
1179                 lockevent_inc(rwsem_sleep_writer);
1180                 set_current_state(state);
1181 trylock_again:
1182                 raw_spin_lock_irq(&sem->wait_lock);
1183         }
1184         __set_current_state(TASK_RUNNING);
1185         raw_spin_unlock_irq(&sem->wait_lock);
1186         lockevent_inc(rwsem_wlock);
1187         trace_contention_end(sem, 0);
1188         return sem;
1189
1190 out_nolock:
1191         __set_current_state(TASK_RUNNING);
1192         raw_spin_lock_irq(&sem->wait_lock);
1193         rwsem_del_wake_waiter(sem, &waiter, &wake_q);
1194         lockevent_inc(rwsem_wlock_fail);
1195         trace_contention_end(sem, -EINTR);
1196         return ERR_PTR(-EINTR);
1197 }
1198
1199 /*
1200  * handle waking up a waiter on the semaphore
1201  * - up_read/up_write has decremented the active part of count if we come here
1202  */
1203 static struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem)
1204 {
1205         unsigned long flags;
1206         DEFINE_WAKE_Q(wake_q);
1207
1208         raw_spin_lock_irqsave(&sem->wait_lock, flags);
1209
1210         if (!list_empty(&sem->wait_list))
1211                 rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
1212
1213         raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
1214         wake_up_q(&wake_q);
1215
1216         return sem;
1217 }
1218
1219 /*
1220  * downgrade a write lock into a read lock
1221  * - caller incremented waiting part of count and discovered it still negative
1222  * - just wake up any readers at the front of the queue
1223  */
1224 static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
1225 {
1226         unsigned long flags;
1227         DEFINE_WAKE_Q(wake_q);
1228
1229         raw_spin_lock_irqsave(&sem->wait_lock, flags);
1230
1231         if (!list_empty(&sem->wait_list))
1232                 rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);
1233
1234         raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
1235         wake_up_q(&wake_q);
1236
1237         return sem;
1238 }
1239
1240 /*
1241  * lock for reading
1242  */
1243 static __always_inline int __down_read_common(struct rw_semaphore *sem, int state)
1244 {
1245         int ret = 0;
1246         long count;
1247
1248         preempt_disable();
1249         if (!rwsem_read_trylock(sem, &count)) {
1250                 if (IS_ERR(rwsem_down_read_slowpath(sem, count, state))) {
1251                         ret = -EINTR;
1252                         goto out;
1253                 }
1254                 DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
1255         }
1256 out:
1257         preempt_enable();
1258         return ret;
1259 }
1260
1261 static __always_inline void __down_read(struct rw_semaphore *sem)
1262 {
1263         __down_read_common(sem, TASK_UNINTERRUPTIBLE);
1264 }
1265
1266 static __always_inline int __down_read_interruptible(struct rw_semaphore *sem)
1267 {
1268         return __down_read_common(sem, TASK_INTERRUPTIBLE);
1269 }
1270
1271 static __always_inline int __down_read_killable(struct rw_semaphore *sem)
1272 {
1273         return __down_read_common(sem, TASK_KILLABLE);
1274 }
1275
1276 static inline int __down_read_trylock(struct rw_semaphore *sem)
1277 {
1278         int ret = 0;
1279         long tmp;
1280
1281         DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
1282
1283         preempt_disable();
1284         tmp = atomic_long_read(&sem->count);
1285         while (!(tmp & RWSEM_READ_FAILED_MASK)) {
1286                 if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
1287                                                     tmp + RWSEM_READER_BIAS)) {
1288                         rwsem_set_reader_owned(sem);
1289                         ret = 1;
1290                         break;
1291                 }
1292         }
1293         preempt_enable();
1294         return ret;
1295 }
1296
1297 /*
1298  * lock for writing
1299  */
1300 static inline int __down_write_common(struct rw_semaphore *sem, int state)
1301 {
1302         int ret = 0;
1303
1304         preempt_disable();
1305         if (unlikely(!rwsem_write_trylock(sem))) {
1306                 if (IS_ERR(rwsem_down_write_slowpath(sem, state)))
1307                         ret = -EINTR;
1308         }
1309         preempt_enable();
1310         return ret;
1311 }
1312
1313 static inline void __down_write(struct rw_semaphore *sem)
1314 {
1315         __down_write_common(sem, TASK_UNINTERRUPTIBLE);
1316 }
1317
1318 static inline int __down_write_killable(struct rw_semaphore *sem)
1319 {
1320         return __down_write_common(sem, TASK_KILLABLE);
1321 }
1322
1323 static inline int __down_write_trylock(struct rw_semaphore *sem)
1324 {
1325         int ret;
1326
1327         preempt_disable();
1328         DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
1329         ret = rwsem_write_trylock(sem);
1330         preempt_enable();
1331
1332         return ret;
1333 }
1334
1335 /*
1336  * unlock after reading
1337  */
1338 static inline void __up_read(struct rw_semaphore *sem)
1339 {
1340         long tmp;
1341
1342         DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
1343         DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
1344
1345         preempt_disable();
1346         rwsem_clear_reader_owned(sem);
1347         tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);
1348         DEBUG_RWSEMS_WARN_ON(tmp < 0, sem);
1349         if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) ==
1350                       RWSEM_FLAG_WAITERS)) {
1351                 clear_nonspinnable(sem);
1352                 rwsem_wake(sem);
1353         }
1354         preempt_enable();
1355 }
1356
1357 /*
1358  * unlock after writing
1359  */
1360 static inline void __up_write(struct rw_semaphore *sem)
1361 {
1362         long tmp;
1363
1364         DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
1365         /*
1366          * sem->owner may differ from current if the ownership is transferred
1367          * to an anonymous writer by setting the RWSEM_NONSPINNABLE bits.
1368          */
1369         DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) &&
1370                             !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE), sem);
1371
1372         preempt_disable();
1373         rwsem_clear_owner(sem);
1374         tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count);
1375         if (unlikely(tmp & RWSEM_FLAG_WAITERS))
1376                 rwsem_wake(sem);
1377         preempt_enable();
1378 }
1379
1380 /*
1381  * downgrade write lock to read lock
1382  */
1383 static inline void __downgrade_write(struct rw_semaphore *sem)
1384 {
1385         long tmp;
1386
1387         /*
1388          * When downgrading from exclusive to shared ownership,
1389          * anything inside the write-locked region cannot leak
1390          * into the read side. In contrast, anything in the
1391          * read-locked region is ok to be re-ordered into the
1392          * write side. As such, rely on RELEASE semantics.
1393          */
1394         DEBUG_RWSEMS_WARN_ON(rwsem_owner(sem) != current, sem);
1395         preempt_disable();
1396         tmp = atomic_long_fetch_add_release(
1397                 -RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count);
1398         rwsem_set_reader_owned(sem);
1399         if (tmp & RWSEM_FLAG_WAITERS)
1400                 rwsem_downgrade_wake(sem);
1401         preempt_enable();
1402 }
1403
1404 #else /* !CONFIG_PREEMPT_RT */
1405
1406 #define RT_MUTEX_BUILD_MUTEX
1407 #include "rtmutex.c"
1408
1409 #define rwbase_set_and_save_current_state(state)        \
1410         set_current_state(state)
1411
1412 #define rwbase_restore_current_state()                  \
1413         __set_current_state(TASK_RUNNING)
1414
1415 #define rwbase_rtmutex_lock_state(rtm, state)           \
1416         __rt_mutex_lock(rtm, state)
1417
1418 #define rwbase_rtmutex_slowlock_locked(rtm, state)      \
1419         __rt_mutex_slowlock_locked(rtm, NULL, state)
1420
1421 #define rwbase_rtmutex_unlock(rtm)                      \
1422         __rt_mutex_unlock(rtm)
1423
1424 #define rwbase_rtmutex_trylock(rtm)                     \
1425         __rt_mutex_trylock(rtm)
1426
1427 #define rwbase_signal_pending_state(state, current)     \
1428         signal_pending_state(state, current)
1429
1430 #define rwbase_pre_schedule()                           \
1431         rt_mutex_pre_schedule()
1432
1433 #define rwbase_schedule()                               \
1434         rt_mutex_schedule()
1435
1436 #define rwbase_post_schedule()                          \
1437         rt_mutex_post_schedule()
1438
1439 #include "rwbase_rt.c"
1440
1441 void __init_rwsem(struct rw_semaphore *sem, const char *name,
1442                   struct lock_class_key *key)
1443 {
1444         init_rwbase_rt(&(sem)->rwbase);
1445
1446 #ifdef CONFIG_DEBUG_LOCK_ALLOC
1447         debug_check_no_locks_freed((void *)sem, sizeof(*sem));
1448         lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
1449 #endif
1450 }
1451 EXPORT_SYMBOL(__init_rwsem);
1452
1453 static inline void __down_read(struct rw_semaphore *sem)
1454 {
1455         rwbase_read_lock(&sem->rwbase, TASK_UNINTERRUPTIBLE);
1456 }
1457
1458 static inline int __down_read_interruptible(struct rw_semaphore *sem)
1459 {
1460         return rwbase_read_lock(&sem->rwbase, TASK_INTERRUPTIBLE);
1461 }
1462
1463 static inline int __down_read_killable(struct rw_semaphore *sem)
1464 {
1465         return rwbase_read_lock(&sem->rwbase, TASK_KILLABLE);
1466 }
1467
1468 static inline int __down_read_trylock(struct rw_semaphore *sem)
1469 {
1470         return rwbase_read_trylock(&sem->rwbase);
1471 }
1472
1473 static inline void __up_read(struct rw_semaphore *sem)
1474 {
1475         rwbase_read_unlock(&sem->rwbase, TASK_NORMAL);
1476 }
1477
1478 static inline void __sched __down_write(struct rw_semaphore *sem)
1479 {
1480         rwbase_write_lock(&sem->rwbase, TASK_UNINTERRUPTIBLE);
1481 }
1482
1483 static inline int __sched __down_write_killable(struct rw_semaphore *sem)
1484 {
1485         return rwbase_write_lock(&sem->rwbase, TASK_KILLABLE);
1486 }
1487
1488 static inline int __down_write_trylock(struct rw_semaphore *sem)
1489 {
1490         return rwbase_write_trylock(&sem->rwbase);
1491 }
1492
1493 static inline void __up_write(struct rw_semaphore *sem)
1494 {
1495         rwbase_write_unlock(&sem->rwbase);
1496 }
1497
1498 static inline void __downgrade_write(struct rw_semaphore *sem)
1499 {
1500         rwbase_write_downgrade(&sem->rwbase);
1501 }
1502
1503 /* Debug stubs for the common API */
1504 #define DEBUG_RWSEMS_WARN_ON(c, sem)
1505
1506 static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
1507                                             struct task_struct *owner)
1508 {
1509 }
1510
1511 static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
1512 {
1513         int count = atomic_read(&sem->rwbase.readers);
1514
1515         return count < 0 && count != READER_BIAS;
1516 }
1517
1518 #endif /* CONFIG_PREEMPT_RT */
1519
1520 /*
1521  * lock for reading
1522  */
1523 void __sched down_read(struct rw_semaphore *sem)
1524 {
1525         might_sleep();
1526         rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
1527
1528         LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
1529 }
1530 EXPORT_SYMBOL(down_read);
1531
1532 int __sched down_read_interruptible(struct rw_semaphore *sem)
1533 {
1534         might_sleep();
1535         rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
1536
1537         if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) {
1538                 rwsem_release(&sem->dep_map, _RET_IP_);
1539                 return -EINTR;
1540         }
1541
1542         return 0;
1543 }
1544 EXPORT_SYMBOL(down_read_interruptible);
1545
1546 int __sched down_read_killable(struct rw_semaphore *sem)
1547 {
1548         might_sleep();
1549         rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
1550
1551         if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
1552                 rwsem_release(&sem->dep_map, _RET_IP_);
1553                 return -EINTR;
1554         }
1555
1556         return 0;
1557 }
1558 EXPORT_SYMBOL(down_read_killable);
1559
1560 /*
1561  * trylock for reading -- returns 1 if successful, 0 if contention
1562  */
1563 int down_read_trylock(struct rw_semaphore *sem)
1564 {
1565         int ret = __down_read_trylock(sem);
1566
1567         if (ret == 1)
1568                 rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
1569         return ret;
1570 }
1571 EXPORT_SYMBOL(down_read_trylock);
1572
1573 /*
1574  * lock for writing
1575  */
1576 void __sched down_write(struct rw_semaphore *sem)
1577 {
1578         might_sleep();
1579         rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
1580         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
1581 }
1582 EXPORT_SYMBOL(down_write);
1583
1584 /*
1585  * lock for writing
1586  */
1587 int __sched down_write_killable(struct rw_semaphore *sem)
1588 {
1589         might_sleep();
1590         rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
1591
1592         if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
1593                                   __down_write_killable)) {
1594                 rwsem_release(&sem->dep_map, _RET_IP_);
1595                 return -EINTR;
1596         }
1597
1598         return 0;
1599 }
1600 EXPORT_SYMBOL(down_write_killable);
1601
1602 /*
1603  * trylock for writing -- returns 1 if successful, 0 if contention
1604  */
1605 int down_write_trylock(struct rw_semaphore *sem)
1606 {
1607         int ret = __down_write_trylock(sem);
1608
1609         if (ret == 1)
1610                 rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
1611
1612         return ret;
1613 }
1614 EXPORT_SYMBOL(down_write_trylock);
1615
1616 /*
1617  * release a read lock
1618  */
1619 void up_read(struct rw_semaphore *sem)
1620 {
1621         rwsem_release(&sem->dep_map, _RET_IP_);
1622         __up_read(sem);
1623 }
1624 EXPORT_SYMBOL(up_read);
1625
1626 /*
1627  * release a write lock
1628  */
1629 void up_write(struct rw_semaphore *sem)
1630 {
1631         rwsem_release(&sem->dep_map, _RET_IP_);
1632         __up_write(sem);
1633 }
1634 EXPORT_SYMBOL(up_write);
1635
1636 /*
1637  * downgrade write lock to read lock
1638  */
1639 void downgrade_write(struct rw_semaphore *sem)
1640 {
1641         lock_downgrade(&sem->dep_map, _RET_IP_);
1642         __downgrade_write(sem);
1643 }
1644 EXPORT_SYMBOL(downgrade_write);
1645
1646 #ifdef CONFIG_DEBUG_LOCK_ALLOC
1647
1648 void down_read_nested(struct rw_semaphore *sem, int subclass)
1649 {
1650         might_sleep();
1651         rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
1652         LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
1653 }
1654 EXPORT_SYMBOL(down_read_nested);
1655
1656 int down_read_killable_nested(struct rw_semaphore *sem, int subclass)
1657 {
1658         might_sleep();
1659         rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
1660
1661         if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
1662                 rwsem_release(&sem->dep_map, _RET_IP_);
1663                 return -EINTR;
1664         }
1665
1666         return 0;
1667 }
1668 EXPORT_SYMBOL(down_read_killable_nested);
1669
1670 void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
1671 {
1672         might_sleep();
1673         rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
1674         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
1675 }
1676 EXPORT_SYMBOL(_down_write_nest_lock);
1677
1678 void down_read_non_owner(struct rw_semaphore *sem)
1679 {
1680         might_sleep();
1681         __down_read(sem);
1682         /*
1683          * The owner value for a reader-owned lock is mostly for debugging
1684          * purpose only and is not critical to the correct functioning of
1685          * rwsem. So it is perfectly fine to set it in a preempt-enabled
1686          * context here.
1687          */
1688         __rwsem_set_reader_owned(sem, NULL);
1689 }
1690 EXPORT_SYMBOL(down_read_non_owner);
1691
1692 void down_write_nested(struct rw_semaphore *sem, int subclass)
1693 {
1694         might_sleep();
1695         rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
1696         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
1697 }
1698 EXPORT_SYMBOL(down_write_nested);
1699
1700 int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
1701 {
1702         might_sleep();
1703         rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
1704
1705         if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
1706                                   __down_write_killable)) {
1707                 rwsem_release(&sem->dep_map, _RET_IP_);
1708                 return -EINTR;
1709         }
1710
1711         return 0;
1712 }
1713 EXPORT_SYMBOL(down_write_killable_nested);
1714
1715 void up_read_non_owner(struct rw_semaphore *sem)
1716 {
1717         DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
1718         __up_read(sem);
1719 }
1720 EXPORT_SYMBOL(up_read_non_owner);
1721
1722 #endif