Date: Sun, 16 Feb 2020 03:14:55 +0000 (UTC) From: Mateusz Guzik <mjg@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r357989 - head/sys/sys Message-ID: <202002160314.01G3Ete9074777@repo.freebsd.org>
next in thread | raw e-mail | index | archive | help
Author: mjg Date: Sun Feb 16 03:14:55 2020 New Revision: 357989 URL: https://svnweb.freebsd.org/changeset/base/357989 Log: refcount: add missing release fence to refcount_release_if_gt The CPU succeeding in releasing the not last reference can still have pending stores to the object protected by the affected counter. This opens a time window where another CPU can release the last reference and free the object, resulting in use-after-free. On top of that this prevents the compiler from generating more accesses to the object regardless of how atomic_fcmpset_rel_int is implemented (of course as long as it provides the release semantic). Reviewed by: markj Modified: head/sys/sys/refcount.h Modified: head/sys/sys/refcount.h ============================================================================== --- head/sys/sys/refcount.h Sun Feb 16 01:07:19 2020 (r357988) +++ head/sys/sys/refcount.h Sun Feb 16 03:14:55 2020 (r357989) @@ -198,7 +198,7 @@ refcount_release_if_gt(volatile u_int *count, u_int n) return (false); if (__predict_false(REFCOUNT_SATURATED(old))) return (true); - if (atomic_fcmpset_int(count, &old, old - 1)) + if (atomic_fcmpset_rel_int(count, &old, old - 1)) return (true); } }
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?202002160314.01G3Ete9074777>