Author: jhb Date: Tue Jan 20 16:35:34 2009 New Revision: 187474 URL: http://svn.freebsd.org/changeset/base/187474
Log: Add a comment explaining why the "bufwait" / "dirhash" LOR reported by WITNESS will not actually result in a deadlock. Discussed with: kib MFC after: 1 week Modified: head/sys/ufs/ufs/ufs_dirhash.c Modified: head/sys/ufs/ufs/ufs_dirhash.c ============================================================================== --- head/sys/ufs/ufs/ufs_dirhash.c Tue Jan 20 14:09:12 2009 (r187473) +++ head/sys/ufs/ufs/ufs_dirhash.c Tue Jan 20 16:35:34 2009 (r187474) @@ -126,6 +126,18 @@ static struct mtx ufsdirhash_mtx; * free a dirhash structure that was recycled by ufsdirhash_recycle(). * * The dirhash lock may be held across io operations. + * + * WITNESS reports a lock order reversal between the "bufwait" lock + * and the "dirhash" lock. However, this specific reversal will not + * cause a deadlock. To get a deadlock, one would have to lock a + * buffer followed by the dirhash while a second thread locked a + * buffer while holding the dirhash lock. The second order can happen + * under a shared or exclusive vnode lock for the associated directory + * in lookup(). The first order, however, can only happen under an + * exclusive vnode lock (e.g. unlink(), rename(), etc.). Thus, for + * a thread to be doing a "bufwait" -> "dirhash" order, it has to hold + * an exclusive vnode lock. That exclusive vnode lock will prevent + * any other threads from doing a "dirhash" -> "bufwait" order. */ static void _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
