625660f8a2fcf0cb4b4b1a9216908c98fffe00a1
[sfrench/cifs-2.6.git] / arch / x86 / include / asm / spinlock.h
1 #ifndef _ASM_X86_SPINLOCK_H
2 #define _ASM_X86_SPINLOCK_H
3
4 #include <linux/jump_label.h>
5 #include <linux/atomic.h>
6 #include <asm/page.h>
7 #include <asm/processor.h>
8 #include <linux/compiler.h>
9 #include <asm/paravirt.h>
10 #include <asm/bitops.h>
11
12 /*
13  * Your basic SMP spinlocks, allowing only a single CPU anywhere
14  *
15  * Simple spin lock operations.  There are two variants, one clears IRQ's
16  * on the local processor, one does not.
17  *
18  * These are fair FIFO ticket locks, which support up to 2^16 CPUs.
19  *
20  * (the type definitions are in asm/spinlock_types.h)
21  */
22
23 #ifdef CONFIG_X86_32
24 # define LOCK_PTR_REG "a"
25 #else
26 # define LOCK_PTR_REG "D"
27 #endif
28
29 #if defined(CONFIG_X86_32) && (defined(CONFIG_X86_PPRO_FENCE))
30 /*
31  * On PPro SMP, we use a locked operation to unlock
32  * (PPro errata 66, 92)
33  */
34 # define UNLOCK_LOCK_PREFIX LOCK_PREFIX
35 #else
36 # define UNLOCK_LOCK_PREFIX
37 #endif
38
39 /* How long a lock should spin before we consider blocking */
40 #define SPIN_THRESHOLD  (1 << 15)
41
42 extern struct static_key paravirt_ticketlocks_enabled;
43 static __always_inline bool static_key_false(struct static_key *key);
44
45 #ifdef CONFIG_PARAVIRT_SPINLOCKS
46
47 static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
48 {
49         set_bit(0, (volatile unsigned long *)&lock->tickets.tail);
50 }
51
52 #else  /* !CONFIG_PARAVIRT_SPINLOCKS */
53 static __always_inline void __ticket_lock_spinning(arch_spinlock_t *lock,
54                                                         __ticket_t ticket)
55 {
56 }
57 static inline void __ticket_unlock_kick(arch_spinlock_t *lock,
58                                                         __ticket_t ticket)
59 {
60 }
61
62 #endif /* CONFIG_PARAVIRT_SPINLOCKS */
63
64 static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
65 {
66         return lock.tickets.head == lock.tickets.tail;
67 }
68
69 /*
70  * Ticket locks are conceptually two parts, one indicating the current head of
71  * the queue, and the other indicating the current tail. The lock is acquired
72  * by atomically noting the tail and incrementing it by one (thus adding
73  * ourself to the queue and noting our position), then waiting until the head
74  * becomes equal to the the initial value of the tail.
75  *
76  * We use an xadd covering *both* parts of the lock, to increment the tail and
77  * also load the position of the head, which takes care of memory ordering
78  * issues and should be optimal for the uncontended case. Note the tail must be
79  * in the high part, because a wide xadd increment of the low part would carry
80  * up and contaminate the high part.
81  */
82 static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
83 {
84         register struct __raw_tickets inc = { .tail = TICKET_LOCK_INC };
85
86         inc = xadd(&lock->tickets, inc);
87         if (likely(inc.head == inc.tail))
88                 goto out;
89
90         inc.tail &= ~TICKET_SLOWPATH_FLAG;
91         for (;;) {
92                 unsigned count = SPIN_THRESHOLD;
93
94                 do {
95                         if (READ_ONCE(lock->tickets.head) == inc.tail)
96                                 goto out;
97                         cpu_relax();
98                 } while (--count);
99                 __ticket_lock_spinning(lock, inc.tail);
100         }
101 out:    barrier();      /* make sure nothing creeps before the lock is taken */
102 }
103
104 static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
105 {
106         arch_spinlock_t old, new;
107
108         old.tickets = READ_ONCE(lock->tickets);
109         if (old.tickets.head != (old.tickets.tail & ~TICKET_SLOWPATH_FLAG))
110                 return 0;
111
112         new.head_tail = old.head_tail + (TICKET_LOCK_INC << TICKET_SHIFT);
113
114         /* cmpxchg is a full barrier, so nothing can move before it */
115         return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) == old.head_tail;
116 }
117
118 static inline void __ticket_unlock_slowpath(arch_spinlock_t *lock,
119                                             arch_spinlock_t old)
120 {
121         arch_spinlock_t new;
122
123         BUILD_BUG_ON(((__ticket_t)NR_CPUS) != NR_CPUS);
124
125         /* Perform the unlock on the "before" copy */
126         old.tickets.head += TICKET_LOCK_INC;
127
128         /* Clear the slowpath flag */
129         new.head_tail = old.head_tail & ~(TICKET_SLOWPATH_FLAG << TICKET_SHIFT);
130
131         /*
132          * If the lock is uncontended, clear the flag - use cmpxchg in
133          * case it changes behind our back though.
134          */
135         if (new.tickets.head != new.tickets.tail ||
136             cmpxchg(&lock->head_tail, old.head_tail,
137                                         new.head_tail) != old.head_tail) {
138                 /*
139                  * Lock still has someone queued for it, so wake up an
140                  * appropriate waiter.
141                  */
142                 __ticket_unlock_kick(lock, old.tickets.head);
143         }
144 }
145
146 static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
147 {
148         if (TICKET_SLOWPATH_FLAG &&
149             static_key_false(&paravirt_ticketlocks_enabled)) {
150                 arch_spinlock_t prev;
151
152                 prev = *lock;
153                 add_smp(&lock->tickets.head, TICKET_LOCK_INC);
154
155                 /* add_smp() is a full mb() */
156
157                 if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG))
158                         __ticket_unlock_slowpath(lock, prev);
159         } else
160                 __add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
161 }
162
163 static inline int arch_spin_is_locked(arch_spinlock_t *lock)
164 {
165         struct __raw_tickets tmp = READ_ONCE(lock->tickets);
166
167         return tmp.tail != tmp.head;
168 }
169
170 static inline int arch_spin_is_contended(arch_spinlock_t *lock)
171 {
172         struct __raw_tickets tmp = READ_ONCE(lock->tickets);
173
174         return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC;
175 }
176 #define arch_spin_is_contended  arch_spin_is_contended
177
178 static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
179                                                   unsigned long flags)
180 {
181         arch_spin_lock(lock);
182 }
183
184 static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
185 {
186         __ticket_t head = ACCESS_ONCE(lock->tickets.head);
187
188         for (;;) {
189                 struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
190                 /*
191                  * We need to check "unlocked" in a loop, tmp.head == head
192                  * can be false positive because of overflow.
193                  */
194                 if (tmp.head == (tmp.tail & ~TICKET_SLOWPATH_FLAG) ||
195                     tmp.head != head)
196                         break;
197
198                 cpu_relax();
199         }
200 }
201
202 /*
203  * Read-write spinlocks, allowing multiple readers
204  * but only one writer.
205  *
206  * NOTE! it is quite common to have readers in interrupts
207  * but no interrupt writers. For those circumstances we
208  * can "mix" irq-safe locks - any writer needs to get a
209  * irq-safe write-lock, but readers can get non-irqsafe
210  * read-locks.
211  *
212  * On x86, we implement read-write locks using the generic qrwlock with
213  * x86 specific optimization.
214  */
215
216 #include <asm/qrwlock.h>
217
218 #define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
219 #define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
220
221 #define arch_spin_relax(lock)   cpu_relax()
222 #define arch_read_relax(lock)   cpu_relax()
223 #define arch_write_relax(lock)  cpu_relax()
224
225 #endif /* _ASM_X86_SPINLOCK_H */