percpu-rw-semaphores: use light/heavy barriers (5c1eabe6) · Commits · 戴 / test

include/linux/percpu-rwsem.h

+7 −13

Original line number	Diff line number	Diff line
		@@ -12,6 +12,9 @@ struct percpu_rw_semaphore {
		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();
		@@ -24,22 +27,12 @@ static inline void percpu_down_read(struct percpu_rw_semaphore *p)
		}
		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)
		{
		/*
		* 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
		light_mb(); /* B, between read of the data and write to p->counter, paired with C */
		this_cpu_dec(*p->counters);
		}

		@@ -61,11 +54,12 @@ static inline void percpu_down_write(struct percpu_rw_semaphore *p)
		synchronize_rcu();
		while (__percpu_count(p->counters))
		msleep(1);
		smp_rmb(); /* paired with smp_mb() in percpu_sem_up_read() */
		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);
		}

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