From a4d1a73370dffa6ac96ee70693fd1bd335bd70fe Mon Sep 17 00:00:00 2001
From: Sverker Eriksson <sverker@erlang.org>
Date: Wed, 8 Apr 2015 17:02:15 +0200
Subject: erts: Fix ets bug in debug VM

Symptom: ASSERT(segtab[seg_ix] == NULL) in alloc_seg() fails.

Remedy: Make sure we set segment pointer to NULL in free_seg()
even when we switch to smaller segtab.
---
 erts/emulator/beam/erl_db_hash.c |  8 +++---
 lib/stdlib/test/ets_SUITE.erl    | 54 +++++++++++++++++++++-------------------
 2 files changed, 33 insertions(+), 29 deletions(-)

diff --git a/erts/emulator/beam/erl_db_hash.c b/erts/emulator/beam/erl_db_hash.c
index 06dac8f161..b1d9eb84bc 100644
--- a/erts/emulator/beam/erl_db_hash.c
+++ b/erts/emulator/beam/erl_db_hash.c
@@ -2402,10 +2402,10 @@ static int alloc_seg(DbTableHash *tb)
 */
 static int free_seg(DbTableHash *tb, int free_records)
 {
-    int seg_ix = (tb->nslots >> SEGSZ_EXP) - 1;
+    const int seg_ix = (tb->nslots >> SEGSZ_EXP) - 1;
+    struct segment** const segtab = SEGTAB(tb);
+    struct ext_segment* const top = (struct ext_segment*) segtab[seg_ix];
     int bytes;
-    struct segment** segtab = SEGTAB(tb);
-    struct ext_segment* top = (struct ext_segment*) segtab[seg_ix];
     int nrecords = 0;
 
     ASSERT(top != NULL); 
@@ -2468,7 +2468,7 @@ static int free_seg(DbTableHash *tb, int free_records)
 		 (void*)top, bytes);
 #ifdef DEBUG
     if (seg_ix > 0) {
-	if (seg_ix < tb->nsegs) SEGTAB(tb)[seg_ix] = NULL;
+        segtab[seg_ix] = NULL;
     } else {
 	SET_SEGTAB(tb, NULL);
     }
diff --git a/lib/stdlib/test/ets_SUITE.erl b/lib/stdlib/test/ets_SUITE.erl
index 8dc8b2c291..5490dae12f 100644
--- a/lib/stdlib/test/ets_SUITE.erl
+++ b/lib/stdlib/test/ets_SUITE.erl
@@ -5000,36 +5000,40 @@ colliding_names(Name) ->
 
 grow_shrink(Config) when is_list(Config) ->
     ?line EtsMem = etsmem(),
-    ?line grow_shrink_0(lists:seq(3071, 5000), EtsMem),
-    ?line verify_etsmem(EtsMem).
 
-grow_shrink_0([N|Ns], EtsMem) ->
-    ?line grow_shrink_1(N, [set]),
-    ?line grow_shrink_1(N, [ordered_set]),
-    %% Verifying ets-memory here takes too long time, since
-    %% lock-free allocators were introduced...
-    %% ?line verify_etsmem(EtsMem),
-    grow_shrink_0(Ns, EtsMem);
-grow_shrink_0([], _) -> ok.
-
-grow_shrink_1(N, Flags) ->
-    ?line T = ets_new(a, Flags),
-    ?line grow_shrink_2(N, N, T),
-    ?line ets:delete(T).
+    Set = ets_new(a, [set]),
+    grow_shrink_0(0, 3071, 3000, 5000, Set),
+    ets:delete(Set),
+
+    %OrdSet = ets_new(a, [ordered_set]),
+    %grow_shrink_0(0, lists:seq(3071, 5000), OrdSet),
+    %ets:delete(OrdSet),
 
-grow_shrink_2(0, Orig, T) ->
-    List = [{I,a} || I <- lists:seq(1, Orig)],
-    List = lists:sort(ets:tab2list(T)),
-    grow_shrink_3(Orig, T);
-grow_shrink_2(N, Orig, T) ->
+    ?line verify_etsmem(EtsMem).
+
+grow_shrink_0(N, _, _, Max, _) when N >= Max ->
+    ok;
+grow_shrink_0(N0, GrowN, ShrinkN, Max, T) ->
+    N1 = grow_shrink_1(N0, GrowN, ShrinkN, T),
+    grow_shrink_0(N1, GrowN, ShrinkN, Max, T).
+
+grow_shrink_1(N0, GrowN, ShrinkN, T) ->
+    N1 = grow_shrink_2(N0+1, N0 + GrowN, T),
+    grow_shrink_3(N1, N1 - ShrinkN, T).
+
+grow_shrink_2(N, GrowTo, _) when N > GrowTo ->
+    %io:format("Grown to ~p\n", [GrowTo]),
+    GrowTo;
+grow_shrink_2(N, GrowTo, T) ->
     true = ets:insert(T, {N,a}),
-    grow_shrink_2(N-1, Orig, T).
+    grow_shrink_2(N+1, GrowTo, T).
 
-grow_shrink_3(0, T) ->
-    [] = ets:tab2list(T);
-grow_shrink_3(N, T) ->
+grow_shrink_3(N, ShrinkTo, _) when N =< ShrinkTo ->
+    %io:format("Shrunk to ~p\n", [ShrinkTo]),
+    ShrinkTo;
+grow_shrink_3(N, ShrinkTo, T) ->
     true = ets:delete(T, N),
-    grow_shrink_3(N-1, T).
+    grow_shrink_3(N-1, ShrinkTo, T).
     
 grow_pseudo_deleted(doc) -> ["Grow a table that still contains pseudo-deleted objects"];
 grow_pseudo_deleted(suite) -> [];
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