On Sun, Feb 16, 2020 at 03:14:55AM +0000, Mateusz Guzik wrote: > 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 I think you should update comment in refcount_release_last() to point to if_gt() as well. And probably annotate this fence with a pointer to acquire in release_last().
> > 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); > } > } _______________________________________________ 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"
