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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;
};
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();
}
static inline void percpu_up_read(struct percpu_rw_semaphore *p)
{
/*
* On X86, write operation in this_cpu_dec serves as a memory unlock
* barrier (i.e. memory accesses may be moved before the write, but
* no memory accesses are moved past the write).
* On other architectures this may not be the case, so we need smp_mb()
* there.
*/
#if defined(CONFIG_X86) && (!defined(CONFIG_X86_PPRO_FENCE) && !defined(CONFIG_X86_OOSTORE))
barrier();
#else
smp_mb();
#endif
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);
smp_rmb(); /* paired with smp_mb() in percpu_sem_up_read() */
}
static inline void percpu_up_write(struct percpu_rw_semaphore *p)
{
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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