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-rw-r--r--include/linux/percpu-rwsem.h89
1 files changed, 89 insertions, 0 deletions
diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
new file mode 100644
index 000000000000..cf80f7e5277f
--- /dev/null
+++ b/include/linux/percpu-rwsem.h
@@ -0,0 +1,89 @@
+#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