Merge from OpenSolaris (24-Jul-2010):

6679140 asymmetric alloc/dealloc activity can induce dynamic variable drops
6679193 dtrace_dynvar walker produces flood of dtrace_dynhash_sink

This finishes a set of merges from the older OpenSolaris releases.
Still the FreeBSD port has many differences that are difficult to
account for but that seems normal given that the kernels are different.

MFC after:	1 week

1 files changed, 64 insertions, 14 deletions

diff --git a/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c b/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
index d796e30..7855f91 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
@@ -22,7 +22,7 @@
  */
 
 /*
- * Copyright 2008 Sun Microsystems, Inc. All rights reserved.
+ * Copyright (c) 2003, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2013, Joyent, Inc. All rights reserved.
  * Copyright (c) 2012 by Delphix. All rights reserved.
  */
@@ -238,6 +238,7 @@ static dtrace_helpers_t *dtrace_deferred_pid;	/* deferred helper list */
 static dtrace_enabling_t *dtrace_retained;	/* list of retained enablings */
 static dtrace_genid_t	dtrace_retained_gen;	/* current retained enab gen */
 static dtrace_dynvar_t	dtrace_dynhash_sink;	/* end of dynamic hash chains */
+static int		dtrace_dynvar_failclean; /* dynvars failed to clean */
 #if !defined(sun)
 static struct mtx	dtrace_unr_mtx;
 MTX_SYSINIT(dtrace_unr_mtx, &dtrace_unr_mtx, "Unique resource identifier", MTX_DEF);
@@ -1558,12 +1559,12 @@ dtrace_dynvar_clean(dtrace_dstate_t *dstate)
 {
 	dtrace_dynvar_t *dirty;
 	dtrace_dstate_percpu_t *dcpu;
-	int i, work = 0;
+	dtrace_dynvar_t **rinsep;
+	int i, j, work = 0;
 
 	for (i = 0; i < NCPU; i++) {
 		dcpu = &dstate->dtds_percpu[i];
-
-		ASSERT(dcpu->dtdsc_rinsing == NULL);
+		rinsep = &dcpu->dtdsc_rinsing;
 
 		/*
 		 * If the dirty list is NULL, there is no dirty work to do.
@@ -1571,14 +1572,62 @@ dtrace_dynvar_clean(dtrace_dstate_t *dstate)
 		if (dcpu->dtdsc_dirty == NULL)
 			continue;
 
-		/*
-		 * If the clean list is non-NULL, then we're not going to do
-		 * any work for this CPU -- it means that there has not been
-		 * a dtrace_dynvar() allocation on this CPU (or from this CPU)
-		 * since the last time we cleaned house.
-		 */
-		if (dcpu->dtdsc_clean != NULL)
+		if (dcpu->dtdsc_rinsing != NULL) {
+			/*
+			 * If the rinsing list is non-NULL, then it is because
+			 * this CPU was selected to accept another CPU's
+			 * dirty list -- and since that time, dirty buffers
+			 * have accumulated.  This is a highly unlikely
+			 * condition, but we choose to ignore the dirty
+			 * buffers -- they'll be picked up a future cleanse.
+			 */
 			continue;
+		}
+
+		if (dcpu->dtdsc_clean != NULL) {
+			/*
+			 * If the clean list is non-NULL, then we're in a
+			 * situation where a CPU has done deallocations (we
+			 * have a non-NULL dirty list) but no allocations (we
+			 * also have a non-NULL clean list).  We can't simply
+			 * move the dirty list into the clean list on this
+			 * CPU, yet we also don't want to allow this condition
+			 * to persist, lest a short clean list prevent a
+			 * massive dirty list from being cleaned (which in
+			 * turn could lead to otherwise avoidable dynamic
+			 * drops).  To deal with this, we look for some CPU
+			 * with a NULL clean list, NULL dirty list, and NULL
+			 * rinsing list -- and then we borrow this CPU to
+			 * rinse our dirty list.
+			 */
+			for (j = 0; j < NCPU; j++) {
+				dtrace_dstate_percpu_t *rinser;
+
+				rinser = &dstate->dtds_percpu[j];
+
+				if (rinser->dtdsc_rinsing != NULL)
+					continue;
+
+				if (rinser->dtdsc_dirty != NULL)
+					continue;
+
+				if (rinser->dtdsc_clean != NULL)
+					continue;
+
+				rinsep = &rinser->dtdsc_rinsing;
+				break;
+			}
+
+			if (j == NCPU) {
+				/*
+				 * We were unable to find another CPU that
+				 * could accept this dirty list -- we are
+				 * therefore unable to clean it now.
+				 */
+				dtrace_dynvar_failclean++;
+				continue;
+			}
+		}
 
 		work = 1;
 
@@ -1595,7 +1644,7 @@ dtrace_dynvar_clean(dtrace_dstate_t *dstate)
 			 * on a hash chain, either the dirty list or the
 			 * rinsing list for some CPU must be non-NULL.)
 			 */
-			dcpu->dtdsc_rinsing = dirty;
+			*rinsep = dirty;
 			dtrace_membar_producer();
 		} while (dtrace_casptr(&dcpu->dtdsc_dirty,
 		    dirty, NULL) != dirty);
@@ -2026,7 +2075,7 @@ retry:
 			ASSERT(clean->dtdv_hashval == DTRACE_DYNHASH_FREE);
 
 			/*
-			 * Now we'll move the clean list to the free list.
+			 * Now we'll move the clean list to our free list.
 			 * It's impossible for this to fail:  the only way
 			 * the free list can be updated is through this
 			 * code path, and only one CPU can own the clean list.
@@ -2039,6 +2088,7 @@ retry:
 			 * owners of the clean lists out before resetting
 			 * the clean lists.
 			 */
+			dcpu = &dstate->dtds_percpu[me];
 			rval = dtrace_casptr(&dcpu->dtdsc_free, NULL, clean);
 			ASSERT(rval == NULL);
 			goto retry;
@@ -4729,7 +4779,7 @@ dtrace_dif_subr(uint_t subr, uint_t rd, uint64_t *regs,
 		int64_t index = (int64_t)tupregs[1].dttk_value;
 		int64_t remaining = (int64_t)tupregs[2].dttk_value;
 		size_t len = dtrace_strlen((char *)s, size);
-		int64_t i = 0;
+		int64_t i;
 
 		if (!dtrace_canload(s, len + 1, mstate, vstate)) {
 			regs[rd] = 0;