refcount: update comments about fencing when releasing counts after r357989
Requested by: kib Reviewed by: kib Differential Revision: https://reviews.freebsd.org/D23719
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svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=358007
@ -368,8 +368,8 @@ refcount_release_last(volatile u_int *count, u_int n, u_int old)
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/*
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* Last reference. Signal the user to call the destructor.
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*
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* Ensure that the destructor sees all updates. The fence_rel
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* at the start of refcount_releasen synchronizes with this fence.
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* Ensure that the destructor sees all updates. This synchronizes
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* with release fences from all routines which drop the count.
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*/
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atomic_thread_fence_acq();
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return (true);
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@ -119,6 +119,9 @@ refcount_releasen(volatile u_int *count, u_int n)
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KASSERT(n < REFCOUNT_SATURATION_VALUE / 2,
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("refcount_releasen: n=%u too large", n));
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/*
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* Paired with acquire fence in refcount_release_last.
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*/
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atomic_thread_fence_rel();
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old = atomic_fetchadd_int(count, -n);
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if (__predict_false(n >= REFCOUNT_COUNT(old) ||
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@ -198,6 +201,9 @@ refcount_release_if_gt(volatile u_int *count, u_int n)
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return (false);
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if (__predict_false(REFCOUNT_SATURATED(old)))
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return (true);
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/*
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* Paired with acquire fence in refcount_release_last.
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*/
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if (atomic_fcmpset_rel_int(count, &old, old - 1))
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return (true);
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}
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