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_QUEUED_SPINLOCK 46 #include <asm/qspinlock.h> 47 #else 48 49 #ifdef CONFIG_PARAVIRT_SPINLOCKS 50 51 static inline void __ticket_enter_slowpath(arch_spinlock_t *lock) 52 { 53 set_bit(0, (volatile unsigned long *)&lock->tickets.head); 54 } 55 56 #else /* !CONFIG_PARAVIRT_SPINLOCKS */ 57 static __always_inline void __ticket_lock_spinning(arch_spinlock_t *lock, 58 __ticket_t ticket) 59 { 60 } 61 static inline void __ticket_unlock_kick(arch_spinlock_t *lock, 62 __ticket_t ticket) 63 { 64 } 65 66 #endif /* CONFIG_PARAVIRT_SPINLOCKS */ 67 static inline int __tickets_equal(__ticket_t one, __ticket_t two) 68 { 69 return !((one ^ two) & ~TICKET_SLOWPATH_FLAG); 70 } 71 72 static inline void __ticket_check_and_clear_slowpath(arch_spinlock_t *lock, 73 __ticket_t head) 74 { 75 if (head & TICKET_SLOWPATH_FLAG) { 76 arch_spinlock_t old, new; 77 78 old.tickets.head = head; 79 new.tickets.head = head & ~TICKET_SLOWPATH_FLAG; 80 old.tickets.tail = new.tickets.head + TICKET_LOCK_INC; 81 new.tickets.tail = old.tickets.tail; 82 83 /* try to clear slowpath flag when there are no contenders */ 84 cmpxchg(&lock->head_tail, old.head_tail, new.head_tail); 85 } 86 } 87 88 static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock) 89 { 90 return __tickets_equal(lock.tickets.head, lock.tickets.tail); 91 } 92 93 /* 94 * Ticket locks are conceptually two parts, one indicating the current head of 95 * the queue, and the other indicating the current tail. The lock is acquired 96 * by atomically noting the tail and incrementing it by one (thus adding 97 * ourself to the queue and noting our position), then waiting until the head 98 * becomes equal to the the initial value of the tail. 99 * 100 * We use an xadd covering *both* parts of the lock, to increment the tail and 101 * also load the position of the head, which takes care of memory ordering 102 * issues and should be optimal for the uncontended case. Note the tail must be 103 * in the high part, because a wide xadd increment of the low part would carry 104 * up and contaminate the high part. 105 */ 106 static __always_inline void arch_spin_lock(arch_spinlock_t *lock) 107 { 108 register struct __raw_tickets inc = { .tail = TICKET_LOCK_INC }; 109 110 inc = xadd(&lock->tickets, inc); 111 if (likely(inc.head == inc.tail)) 112 goto out; 113 114 for (;;) { 115 unsigned count = SPIN_THRESHOLD; 116 117 do { 118 inc.head = READ_ONCE(lock->tickets.head); 119 if (__tickets_equal(inc.head, inc.tail)) 120 goto clear_slowpath; 121 cpu_relax(); 122 } while (--count); 123 __ticket_lock_spinning(lock, inc.tail); 124 } 125 clear_slowpath: 126 __ticket_check_and_clear_slowpath(lock, inc.head); 127 out: 128 barrier(); /* make sure nothing creeps before the lock is taken */ 129 } 130 131 static __always_inline int arch_spin_trylock(arch_spinlock_t *lock) 132 { 133 arch_spinlock_t old, new; 134 135 old.tickets = READ_ONCE(lock->tickets); 136 if (!__tickets_equal(old.tickets.head, old.tickets.tail)) 137 return 0; 138 139 new.head_tail = old.head_tail + (TICKET_LOCK_INC << TICKET_SHIFT); 140 new.head_tail &= ~TICKET_SLOWPATH_FLAG; 141 142 /* cmpxchg is a full barrier, so nothing can move before it */ 143 return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) == old.head_tail; 144 } 145 146 static __always_inline void arch_spin_unlock(arch_spinlock_t *lock) 147 { 148 if (TICKET_SLOWPATH_FLAG && 149 static_key_false(¶virt_ticketlocks_enabled)) { 150 __ticket_t head; 151 152 BUILD_BUG_ON(((__ticket_t)NR_CPUS) != NR_CPUS); 153 154 head = xadd(&lock->tickets.head, TICKET_LOCK_INC); 155 156 if (unlikely(head & TICKET_SLOWPATH_FLAG)) { 157 head &= ~TICKET_SLOWPATH_FLAG; 158 __ticket_unlock_kick(lock, (head + TICKET_LOCK_INC)); 159 } 160 } else 161 __add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX); 162 } 163 164 static inline int arch_spin_is_locked(arch_spinlock_t *lock) 165 { 166 struct __raw_tickets tmp = READ_ONCE(lock->tickets); 167 168 return !__tickets_equal(tmp.tail, tmp.head); 169 } 170 171 static inline int arch_spin_is_contended(arch_spinlock_t *lock) 172 { 173 struct __raw_tickets tmp = READ_ONCE(lock->tickets); 174 175 tmp.head &= ~TICKET_SLOWPATH_FLAG; 176 return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC; 177 } 178 #define arch_spin_is_contended arch_spin_is_contended 179 180 static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock, 181 unsigned long flags) 182 { 183 arch_spin_lock(lock); 184 } 185 186 static inline void arch_spin_unlock_wait(arch_spinlock_t *lock) 187 { 188 __ticket_t head = READ_ONCE(lock->tickets.head); 189 190 for (;;) { 191 struct __raw_tickets tmp = READ_ONCE(lock->tickets); 192 /* 193 * We need to check "unlocked" in a loop, tmp.head == head 194 * can be false positive because of overflow. 195 */ 196 if (__tickets_equal(tmp.head, tmp.tail) || 197 !__tickets_equal(tmp.head, head)) 198 break; 199 200 cpu_relax(); 201 } 202 } 203 #endif /* CONFIG_QUEUED_SPINLOCK */ 204 205 /* 206 * Read-write spinlocks, allowing multiple readers 207 * but only one writer. 208 * 209 * NOTE! it is quite common to have readers in interrupts 210 * but no interrupt writers. For those circumstances we 211 * can "mix" irq-safe locks - any writer needs to get a 212 * irq-safe write-lock, but readers can get non-irqsafe 213 * read-locks. 214 * 215 * On x86, we implement read-write locks using the generic qrwlock with 216 * x86 specific optimization. 217 */ 218 219 #include <asm/qrwlock.h> 220 221 #define arch_read_lock_flags(lock, flags) arch_read_lock(lock) 222 #define arch_write_lock_flags(lock, flags) arch_write_lock(lock) 223 224 #define arch_spin_relax(lock) cpu_relax() 225 #define arch_read_relax(lock) cpu_relax() 226 #define arch_write_relax(lock) cpu_relax() 227 228 #endif /* _ASM_X86_SPINLOCK_H */ 229