Commit b393e8b3 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

percpu: READ_ONCE() now implies smp_read_barrier_depends() 



Because READ_ONCE() now implies smp_read_barrier_depends(), this commit
removes the now-redundant smp_read_barrier_depends() following the
READ_ONCE() in __ref_is_percpu().

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
parent 7088efa9

include/linux/percpu-refcount.h

+3 −3
Original line number Diff line number Diff line
@@ -139,12 +139,12 @@ static inline bool __ref_is_percpu(struct percpu_ref *ref, 
	 * when using it as a pointer, __PERCPU_REF_ATOMIC may be set in

	 * between contaminating the pointer value, meaning that

	 * READ_ONCE() is required when fetching it.

	 *

	 * The smp_read_barrier_depends() implied by READ_ONCE() pairs

	 * with smp_store_release() in __percpu_ref_switch_to_percpu().

	 */

	percpu_ptr = READ_ONCE(ref->percpu_count_ptr);



	/* paired with smp_store_release() in __percpu_ref_switch_to_percpu() */

	smp_read_barrier_depends();



	/*

	 * Theoretically, the following could test just ATOMIC; however,

	 * then we'd have to mask off DEAD separately as DEAD may be

lib/percpu-refcount.c

+4 −4
Original line number Diff line number Diff line
@@ -197,10 +197,10 @@ static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref) 
	atomic_long_add(PERCPU_COUNT_BIAS, &ref->count);



	/*

	 * Restore per-cpu operation.  smp_store_release() is paired with

	 * smp_read_barrier_depends() in __ref_is_percpu() and guarantees

	 * that the zeroing is visible to all percpu accesses which can see

	 * the following __PERCPU_REF_ATOMIC clearing.

	 * Restore per-cpu operation.  smp_store_release() is paired

	 * with READ_ONCE() in __ref_is_percpu() and guarantees that the

	 * zeroing is visible to all percpu accesses which can see the

	 * following __PERCPU_REF_ATOMIC clearing.

	 */

	for_each_possible_cpu(cpu)

		*per_cpu_ptr(percpu_count, cpu) = 0;

CRA Git | Maintained and supported by SUSTech CRA and CCSE