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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: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
hifive-unleashed-5.1
Paul E. McKenney 2017-10-09 10:20:44 -07:00
parent 7088efa913
commit b393e8b33e
2 changed files with 7 additions and 7 deletions
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6
include/linux/percpu-refcount.h
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@ -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

8
lib/percpu-refcount.c
View File

@ -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;