Author: mjg Date: Sun Feb 16 18:20:09 2020 New Revision: 358007 URL: https://svnweb.freebsd.org/changeset/base/358007
Log: refcount: update comments about fencing when releasing counts after r357989 Requested by: kib Reviewed by: kib Differential Revision: https://reviews.freebsd.org/D23719 Modified: head/sys/kern/kern_synch.c head/sys/sys/refcount.h Modified: head/sys/kern/kern_synch.c ============================================================================== --- head/sys/kern/kern_synch.c Sun Feb 16 17:55:32 2020 (r358006) +++ head/sys/kern/kern_synch.c Sun Feb 16 18:20:09 2020 (r358007) @@ -368,8 +368,8 @@ refcount_release_last(volatile u_int *count, u_int n, /* * Last reference. Signal the user to call the destructor. * - * Ensure that the destructor sees all updates. The fence_rel - * at the start of refcount_releasen synchronizes with this fence. + * Ensure that the destructor sees all updates. This synchronizes + * with release fences from all routines which drop the count. */ atomic_thread_fence_acq(); return (true); Modified: head/sys/sys/refcount.h ============================================================================== --- head/sys/sys/refcount.h Sun Feb 16 17:55:32 2020 (r358006) +++ head/sys/sys/refcount.h Sun Feb 16 18:20:09 2020 (r358007) @@ -119,6 +119,9 @@ refcount_releasen(volatile u_int *count, u_int n) KASSERT(n < REFCOUNT_SATURATION_VALUE / 2, ("refcount_releasen: n=%u too large", n)); + /* + * Paired with acquire fence in refcount_release_last. + */ atomic_thread_fence_rel(); old = atomic_fetchadd_int(count, -n); if (__predict_false(n >= REFCOUNT_COUNT(old) || @@ -198,6 +201,9 @@ refcount_release_if_gt(volatile u_int *count, u_int n) return (false); if (__predict_false(REFCOUNT_SATURATED(old))) return (true); + /* + * Paired with acquire fence in refcount_release_last. + */ if (atomic_fcmpset_rel_int(count, &old, old - 1)) return (true); } _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
