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#ifndef _LINUX_PERCPU_RWSEM_H
#define _LINUX_PERCPU_RWSEM_H
#include <linux/mutex.h>
#include <linux/percpu.h>
#include <linux/rcupdate.h>
#include <linux/delay.h>
struct percpu_rw_semaphore {
unsigned __percpu *counters;
bool locked;
struct mutex mtx;
};
#define light_mb() barrier()
#define heavy_mb() synchronize_sched()
static inline void percpu_down_read(struct percpu_rw_semaphore *p)
{
rcu_read_lock();
if (unlikely(p->locked)) {
rcu_read_unlock();
mutex_lock(&p->mtx);
this_cpu_inc(*p->counters);
mutex_unlock(&p->mtx);
return;
}
this_cpu_inc(*p->counters);
rcu_read_unlock();
light_mb(); /* A, between read of p->locked and read of data, paired with D */
}
static inline void percpu_up_read(struct percpu_rw_semaphore *p)
{
light_mb(); /* B, between read of the data and write to p->counter, paired with C */
this_cpu_dec(*p->counters);
}
static inline unsigned __percpu_count(unsigned __percpu *counters)
{
unsigned total = 0;
int cpu;
for_each_possible_cpu(cpu)
total += ACCESS_ONCE(*per_cpu_ptr(counters, cpu));
return total;
}
static inline void percpu_down_write(struct percpu_rw_semaphore *p)
{
mutex_lock(&p->mtx);
p->locked = true;
synchronize_rcu();
while (__percpu_count(p->counters))
msleep(1);
heavy_mb(); /* C, between read of p->counter and write to data, paired with B */
}
static inline void percpu_up_write(struct percpu_rw_semaphore *p)
{
heavy_mb(); /* D, between write to data and write to p->locked, paired with A */
p->locked = false;
mutex_unlock(&p->mtx);
}
static inline int percpu_init_rwsem(struct percpu_rw_semaphore *p)
{
p->counters = alloc_percpu(unsigned);
if (unlikely(!p->counters))
return -ENOMEM;
p->locked = false;
mutex_init(&p->mtx);
return 0;
}
static inline void percpu_free_rwsem(struct percpu_rw_semaphore *p)
{
free_percpu(p->counters);
p->counters = NULL; /* catch use after free bugs */
}
#endif
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