include/linux/bit_spinlock.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef __LINUX_BIT_SPINLOCK_H
   3 #define __LINUX_BIT_SPINLOCK_H
   4
   5 #include <linux/kernel.h>
   6 #include <linux/preempt.h>
   7 #include <linux/atomic.h>
   8 #include <linux/bug.h>
   9
  10 /*
  11  *  bit-based spin_lock()
  12  *
  13  * Don't use this unless you really need to: spin_lock() and spin_unlock()
  14  * are significantly faster.
  15  */
  16 static inline void bit_spin_lock(int bitnum, unsigned long *addr)
  17 {
  18         /*
  19          * Assuming the lock is uncontended, this never enters
  20          * the body of the outer loop. If it is contended, then
  21          * within the inner loop a non-atomic test is used to
  22          * busywait with less bus contention for a good time to
  23          * attempt to acquire the lock bit.
  24          */
  25         preempt_disable();
  26 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
  27         while (unlikely(test_and_set_bit_lock(bitnum, addr))) {
  28                 preempt_enable();
  29                 do {
  30                         cpu_relax();
  31                 } while (test_bit(bitnum, addr));
  32                 preempt_disable();
  33         }
  34 #endif
  35         __acquire(bitlock);
  36 }
  37
  38 /*
  39  * Return true if it was acquired
  40  */
  41 static inline int bit_spin_trylock(int bitnum, unsigned long *addr)
  42 {
  43         preempt_disable();
  44 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
  45         if (unlikely(test_and_set_bit_lock(bitnum, addr))) {
  46                 preempt_enable();
  47                 return 0;
  48         }
  49 #endif
  50         __acquire(bitlock);
  51         return 1;
  52 }
  53
  54 /*
  55  *  bit-based spin_unlock()
  56  */
  57 static inline void bit_spin_unlock(int bitnum, unsigned long *addr)
  58 {
  59 #ifdef CONFIG_DEBUG_SPINLOCK
  60         BUG_ON(!test_bit(bitnum, addr));
  61 #endif
  62 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
  63         clear_bit_unlock(bitnum, addr);
  64 #endif
  65         preempt_enable();
  66         __release(bitlock);
  67 }
  68
  69 /*
  70  *  bit-based spin_unlock()
  71  *  non-atomic version, which can be used eg. if the bit lock itself is
  72  *  protecting the rest of the flags in the word.
  73  */
  74 static inline void __bit_spin_unlock(int bitnum, unsigned long *addr)
  75 {
  76 #ifdef CONFIG_DEBUG_SPINLOCK
  77         BUG_ON(!test_bit(bitnum, addr));
  78 #endif
  79 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
  80         __clear_bit_unlock(bitnum, addr);
  81 #endif
  82         preempt_enable();
  83         __release(bitlock);
  84 }
  85
  86 /*
  87  * Return true if the lock is held.
  88  */
  89 static inline int bit_spin_is_locked(int bitnum, unsigned long *addr)
  90 {
  91 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
  92         return test_bit(bitnum, addr);
  93 #elif defined CONFIG_PREEMPT_COUNT
  94         return preempt_count();
  95 #else
  96         return 1;
  97 #endif
  98 }
  99
 100 #endif /* __LINUX_BIT_SPINLOCK_H */
 101