Merge branch 'dgud/mnesia/del_schema_hangs/OTP-13284' into maint

* dgud/mnesia/del_schema_hangs/OTP-13284:
  mnesia: let loader check if tablelock is needed
  mnesia: Avoid deadlock possibility in mnesia:del_table_copy schema

6 files changed, 150 insertions, 185 deletions

diff --git a/lib/mnesia/src/mnesia_controller.erl b/lib/mnesia/src/mnesia_controller.erl
index 02c175760e..69ccc1d2c9 100644
--- a/lib/mnesia/src/mnesia_controller.erl
+++ b/lib/mnesia/src/mnesia_controller.erl
@@ -78,7 +78,7 @@
 	 change_table_majority/1,
 	 del_active_replica/2,
 	 wait_for_tables/2,
-	 get_network_copy/2,
+	 get_network_copy/3,
 	 merge_schema/0,
 	 start_remote_sender/4,
 	 schedule_late_disc_load/2
@@ -329,14 +329,14 @@ release_schema_commit_lock() ->
     unlink(whereis(?SERVER_NAME)).
 
 %% Special for preparation of add table copy
-get_network_copy(Tab, Cs) ->
+get_network_copy(Tid, Tab, Cs) ->
 %   We can't let the controller queue this one
 %   because that may cause a deadlock between schema_operations
 %   and initial tableloadings which both takes schema locks.
 %   But we have to get copier_done msgs when the other side
 %   goes down.
     call({add_other, self()}),
-    Reason = {dumper,add_table_copy},
+    Reason = {dumper,{add_table_copy, Tid}},
     Work = #net_load{table = Tab,reason = Reason,cstruct = Cs},
     %% I'll need this cause it's linked trough the subscriber
     %% might be solved by using monitor in subscr instead.
@@ -775,7 +775,7 @@ handle_call({net_load, Tab, Cs}, From, State) ->
 	    true ->
 		Worker = #net_load{table = Tab,
 				   opt_reply_to = From,
-				   reason = {dumper,add_table_copy},
+				   reason = {dumper,{add_table_copy, unknown}},
 				   cstruct = Cs
 				  },
 		add_worker(Worker, State);
@@ -1180,11 +1180,11 @@ handle_info(Done = #loader_done{worker_pid=WPid, table_name=Tab}, State0) ->
 		    Done#loader_done.needs_announce == true,
 		    Done#loader_done.needs_reply == true ->
 			i_have_tab(Tab),
-			%% Should be {dumper,add_table_copy} only
+			%% Should be {dumper,{add_table_copy, _}} only
 			reply(Done#loader_done.reply_to,
 			      Done#loader_done.reply);
 		    Done#loader_done.needs_reply == true ->
-			%% Should be {dumper,add_table_copy} only
+			%% Should be {dumper,{add_table_copy,_}} only
 			reply(Done#loader_done.reply_to,
 			      Done#loader_done.reply);
 		    Done#loader_done.needs_announce == true, Tab == schema ->
@@ -2148,6 +2148,10 @@ load_table_fun(#net_load{cstruct=Cs, table=Tab, reason=Reason, opt_reply_to=Repl
 			reply_to = ReplyTo,
 			reply = {loaded, ok}
 		       },
+    AddTableCopy = case Reason of
+		       {dumper,{add_table_copy,_}} -> true;
+		       _ -> false
+		   end,
     if
 	ReadNode == node() ->
 	    %% Already loaded locally
@@ -2157,7 +2161,7 @@ load_table_fun(#net_load{cstruct=Cs, table=Tab, reason=Reason, opt_reply_to=Repl
 		    Res = mnesia_loader:disc_load_table(Tab, load_local_content),
 		    Done#loader_done{reply = Res, needs_announce = true, needs_sync = true}
 	    end;
-	AccessMode == read_only, Reason /= {dumper,add_table_copy} ->
+	AccessMode == read_only, not AddTableCopy ->
 	    fun() -> disc_load_table(Tab, Reason, ReplyTo) end;
 	true ->
 	    fun() ->
diff --git a/lib/mnesia/src/mnesia_loader.erl b/lib/mnesia/src/mnesia_loader.erl
index da8549be50..41fcd76fcb 100644
--- a/lib/mnesia/src/mnesia_loader.erl
+++ b/lib/mnesia/src/mnesia_loader.erl
@@ -180,8 +180,7 @@ do_get_disc_copy2(Tab, Reason, Storage, Type) when Storage == disc_only_copies -
 -define(MAX_RAM_TRANSFERS, (?MAX_RAM_FILE_SIZE div ?MAX_TRANSFER_SIZE) + 1).
 -define(MAX_NOPACKETS, 20).
 
-net_load_table(Tab, Reason, Ns, Cs)
-        when Reason == {dumper,add_table_copy} ->
+net_load_table(Tab, {dumper,{add_table_copy, _}}=Reason, Ns, Cs) ->
     try_net_load_table(Tab, Reason, Ns, Cs);
 net_load_table(Tab, Reason, Ns, _Cs) ->
     try_net_load_table(Tab, Reason, Ns, val({Tab, cstruct})).
@@ -233,7 +232,8 @@ do_snmpify(Tab, Us, Storage) ->
     set({Tab, {index, snmp}}, Snmp).
 
 %% Start the recieiver
-init_receiver(Node, Tab, Storage, Cs, Reas={dumper,add_table_copy}) ->
+init_receiver(Node, Tab, Storage, Cs, Reas={dumper,{add_table_copy, Tid}}) ->
+    rpc:call(Node, mnesia_lib, set, [{?MODULE, active_trans}, Tid]),
     case start_remote_sender(Node, Tab, Storage) of
 	{SenderPid, TabSize, DetsData} ->
 	    start_receiver(Tab,Storage,Cs,SenderPid,TabSize,DetsData,Reas);
@@ -307,7 +307,7 @@ table_init_fun(SenderPid) ->
     end.
 
 %% Add_table_copy get's it's own locks.
-start_receiver(Tab,Storage,Cs,SenderPid,TabSize,DetsData,{dumper,add_table_copy}) ->
+start_receiver(Tab,Storage,Cs,SenderPid,TabSize,DetsData,{dumper,{add_table_copy,_}}) ->
     Init = table_init_fun(SenderPid),
     case do_init_table(Tab,Storage,Cs,SenderPid,TabSize,DetsData,self(), Init) of
 	Err = {error, _} ->
@@ -658,9 +658,10 @@ send_table(Pid, Tab, RemoteS) ->
 	    {Init, Chunk} = reader_funcs(UseDetsChunk, Tab, Storage, KeysPerTransfer),
 
 	    SendIt = fun() ->
-			     {atomic, ok} = prepare_copy(Pid, Tab, Storage),
+			     NeedLock = need_lock(Tab),
+			     {atomic, ok} = prepare_copy(Pid, Tab, Storage, NeedLock),
 			     send_more(Pid, 1, Chunk, Init(), Tab),
-			     finish_copy(Pid, Tab, Storage, RemoteS)
+			     finish_copy(Pid, Tab, Storage, RemoteS, NeedLock)
 		     end,
 
 	    try SendIt() of
@@ -678,10 +679,10 @@ send_table(Pid, Tab, RemoteS) ->
 	    end
     end.
 
-prepare_copy(Pid, Tab, Storage) ->
+prepare_copy(Pid, Tab, Storage, NeedLock) ->
     Trans =
 	fun() ->
-		mnesia:lock_table(Tab, load),
+		NeedLock andalso mnesia:lock_table(Tab, load),
 		mnesia_subscr:subscribe(Pid, {table, Tab}),
 		update_where_to_write(Tab, node(Pid)),
 		mnesia_lib:db_fixtable(Storage, Tab, true),
@@ -689,6 +690,21 @@ prepare_copy(Pid, Tab, Storage) ->
 	end,
     mnesia:transaction(Trans).
 
+
+need_lock(Tab) ->
+    case ?catch_val({?MODULE, active_trans}) of
+	#tid{} = Tid ->
+	    %% move_table_copy grabs it's own table-lock
+	    %% do not deadlock with it
+	    mnesia_lib:unset({?MODULE, active_trans}),
+	    case mnesia_locker:get_held_locks(Tab) of
+		[{write, Tid}|_] -> false;
+		_Locks -> true
+	    end;
+	_ ->
+	    true
+    end.
+
 update_where_to_write(Tab, Node) ->
     case val({Tab, access_mode}) of
 	read_only ->
@@ -783,12 +799,12 @@ send_packet(N, Pid, Chunk, {Recs, Cont}) when N < ?MAX_NOPACKETS ->
 send_packet(_N, _Pid, _Chunk, DataState) ->
     DataState.
 
-finish_copy(Pid, Tab, Storage, RemoteS) ->
+finish_copy(Pid, Tab, Storage, RemoteS, NeedLock) ->
     RecNode = node(Pid),
     DatBin = dat2bin(Tab, Storage, RemoteS),
     Trans =
 	fun() ->
-		mnesia:read_lock_table(Tab),
+		NeedLock andalso mnesia:read_lock_table(Tab),
 		A = val({Tab, access_mode}),
 		mnesia_controller:sync_and_block_table_whereabouts(Tab, RecNode, RemoteS, A),
 		cleanup_tab_copier(Pid, Storage, Tab),
diff --git a/lib/mnesia/src/mnesia_locker.erl b/lib/mnesia/src/mnesia_locker.erl
index 89feeba2c3..5766f22e92 100644
--- a/lib/mnesia/src/mnesia_locker.erl
+++ b/lib/mnesia/src/mnesia_locker.erl
@@ -22,7 +22,7 @@
 -module(mnesia_locker).
 
 -export([
-	 get_held_locks/0,
+	 get_held_locks/0, get_held_locks/1,
 	 get_lock_queue/0,
 	 global_lock/5,
 	 ixrlock/5,
@@ -236,6 +236,11 @@ loop(State) ->
 	    From ! {Ref, ok},
 	    loop(State);
 
+	{From, {is_locked, Oid}} ->
+	    Held = ?ets_lookup(mnesia_held_locks, Oid),
+	    reply(From, Held),
+	    loop(State);
+
 	{'EXIT', Pid, _} when Pid == State#state.supervisor ->
 	    do_stop();
 
@@ -1151,6 +1156,19 @@ get_held_locks() ->
     Locks = receive {mnesia_held_locks, Ls} -> Ls after 5000 -> [] end,
     rewrite_locks(Locks, []).
 
+%% Mnesia internal usage only
+get_held_locks(Tab) when is_atom(Tab) ->
+    Oid = {Tab, ?ALL},
+    ?MODULE ! {self(), {is_locked, Oid}},
+    receive
+	{?MODULE, _Node, Locks} ->
+	    case Locks of
+		[] -> [];
+		[{Oid, _Prev, What}] -> What
+	    end
+    end.
+
+
 rewrite_locks([{Oid, _, Ls}|Locks], Acc0) ->
     Acc = rewrite_locks(Ls, Oid, Acc0),
     rewrite_locks(Locks, Acc);
diff --git a/lib/mnesia/src/mnesia_monitor.erl b/lib/mnesia/src/mnesia_monitor.erl
index 8313c3bda5..081d746257 100644
--- a/lib/mnesia/src/mnesia_monitor.erl
+++ b/lib/mnesia/src/mnesia_monitor.erl
@@ -82,9 +82,9 @@
 		going_down = [], tm_started = false, early_connects = [],
 		connecting, mq = [], remote_node_status = []}).
 
--define(current_protocol_version,  {8,1}).
+-define(current_protocol_version,  {8,2}).
 
--define(previous_protocol_version, {8,0}).
+-define(previous_protocol_version, {8,1}).
 
 start() ->
     gen_server:start_link({local, ?MODULE}, ?MODULE,
@@ -193,7 +193,7 @@ protocol_version() ->
 %% A sorted list of acceptable protocols the
 %% preferred protocols are first in the list
 acceptable_protocol_versions() ->
-    [protocol_version(), ?previous_protocol_version, {7,6}].
+    [protocol_version(), ?previous_protocol_version].
 
 needs_protocol_conversion(Node) ->
     case {?catch_val({protocol, Node}), protocol_version()} of
@@ -424,8 +424,6 @@ handle_call({negotiate_protocol, Mon, Version, Protocols}, From, State)
 	    case hd(Protocols) of
 		?previous_protocol_version ->
 		    accept_protocol(Mon, MyVersion, ?previous_protocol_version, From, State);
-		{7,6} ->
-		    accept_protocol(Mon, MyVersion, {7,6}, From, State);
 		_ ->
 		    verbose("Connection with ~p rejected. "
 			    "version = ~p, protocols = ~p, "
diff --git a/lib/mnesia/src/mnesia_schema.erl b/lib/mnesia/src/mnesia_schema.erl
index 593360415d..1bd8703e1d 100644
--- a/lib/mnesia/src/mnesia_schema.erl
+++ b/lib/mnesia/src/mnesia_schema.erl
@@ -646,54 +646,18 @@ cs2list(Cs) when is_record(Cs, cstruct) ->
     rec2list(Tags, Tags, 2, Cs);
 cs2list(CreateList) when is_list(CreateList) ->
     CreateList;
-%% 4.6
+
+%% since 4.6
 cs2list(Cs) when element(1, Cs) == cstruct, tuple_size(Cs) == 19 ->
     Tags = [name,type,ram_copies,disc_copies,disc_only_copies,
 	    load_order,access_mode,majority,index,snmp,local_content,
 	    record_name,attributes,
 	    user_properties,frag_properties,storage_properties,
 	    cookie,version],
-    rec2list(Tags, Tags, 2, Cs);
-%% 4.4.19
-cs2list(Cs) when element(1, Cs) == cstruct, tuple_size(Cs) == 18 ->
-    Tags = [name,type,ram_copies,disc_copies,disc_only_copies,
-	    load_order,access_mode,majority,index,snmp,local_content,
-	    record_name,attributes,user_properties,frag_properties,
-	    cookie,version],
-    rec2list(Tags, Tags, 2, Cs);
-%% 4.4.18 and earlier
-cs2list(Cs) when element(1, Cs) == cstruct, tuple_size(Cs) == 17 ->
-    Tags = [name,type,ram_copies,disc_copies,disc_only_copies,
-	    load_order,access_mode,index,snmp,local_content,
-	    record_name,attributes,user_properties,frag_properties,
-	    cookie,version],
     rec2list(Tags, Tags, 2, Cs).
 
 cs2list(false, Cs) ->
-    cs2list(Cs);
-cs2list(ver4_4_18, Cs) -> %% Or earlier
-    Orig = record_info(fields, cstruct),
-    Tags = [name,type,ram_copies,disc_copies,disc_only_copies,
-	    load_order,access_mode,index,snmp,local_content,
-	    record_name,attributes,user_properties,frag_properties,
-	    cookie,version],
-    rec2list(Tags, Orig, 2, Cs);
-cs2list(ver4_4_19, Cs) ->
-    Orig = record_info(fields, cstruct),
-    Tags = [name,type,ram_copies,disc_copies,disc_only_copies,
-	    load_order,access_mode,majority,index,snmp,local_content,
-	    record_name,attributes,user_properties,frag_properties,
-	    cookie,version],
-    rec2list(Tags, Orig, 2, Cs);
-cs2list(ver4_6, Cs) ->
-    Orig = record_info(fields, cstruct),
-    Tags = [name,type,ram_copies,disc_copies,disc_only_copies,
-	    load_order,access_mode,majority,index,snmp,local_content,
-	    record_name,attributes,
-	    user_properties,frag_properties,storage_properties,
-	    cookie,version],
-    rec2list(Tags, Orig, 2, Cs).
-
+    cs2list(Cs).
 
 rec2list([Tag | Tags], [Tag | Orig], Pos, Rec) ->
     Val = element(Pos, Rec),
@@ -703,19 +667,8 @@ rec2list([], _, _Pos, _Rec) ->
 rec2list(Tags, [_|Orig], Pos, Rec) ->
     rec2list(Tags, Orig, Pos+1, Rec).
 
-normalize_cs(Cstructs, Node) ->
-    %% backward-compatibility hack; normalize before returning
-    case need_old_cstructs([Node]) of
-	false ->
-	    Cstructs;
-	Version ->
-	    %% some other format
-	    [convert_cs(Version, Cs) || Cs <- Cstructs]
-    end.
-
-convert_cs(Version, Cs) ->
-    Fields = [Value || {_, Value} <- cs2list(Version, Cs)],
-    list_to_tuple([cstruct|Fields]).
+normalize_cs(Cstructs, _Node) ->
+    Cstructs.
 
 list2cs(List) when is_list(List) ->
     Name = pick(unknown, name, List, must),
@@ -1297,6 +1250,7 @@ make_del_table_copy(Tab, Node) ->
         _ ->
 	    ensure_active(Cs),
             verify_cstruct(Cs2),
+	    get_tid_ts_and_lock(Tab, write),
             [{op, del_table_copy, Storage, Node, vsn_cs2list(Cs2)}]
     end.
 
@@ -1324,6 +1278,7 @@ remove_node_from_tabs([Tab|Rest], Node) ->
 		     remove_node_from_tabs(Rest, Node)];
 		_Ns ->
 		    verify_cstruct(Cs2),
+		    get_tid_ts_and_lock(Tab, write),
 		    [{op, del_table_copy, ram_copies, Node, vsn_cs2list(Cs2)}|
 		     remove_node_from_tabs(Rest, Node)]
 	    end
@@ -1355,6 +1310,11 @@ do_move_table(schema, _FromNode, _ToNode) ->
     mnesia:abort({bad_type, schema});
 do_move_table(Tab, FromNode, ToNode) when is_atom(FromNode), is_atom(ToNode) ->
     TidTs = get_tid_ts_and_lock(schema, write),
+    AnyOld = lists:any(fun(Node) -> mnesia_monitor:needs_protocol_conversion(Node) end,
+		       [ToNode|val({Tab, where_to_write})]),
+    if AnyOld -> ignore;  %% Leads to deadlock on old nodes
+       true -> get_tid_ts_and_lock(Tab, write)
+    end,
     insert_schema_ops(TidTs, make_move_table(Tab, FromNode, ToNode));
 do_move_table(Tab, FromNode, ToNode) ->
     mnesia:abort({badarg, Tab, FromNode, ToNode}).
@@ -1962,7 +1922,7 @@ prepare_op(Tid, {op, add_table_copy, Storage, Node, TabDef}, _WaitFor) ->
 	    end,
 	    %% Tables are created by mnesia_loader get_network code
 	    insert_cstruct(Tid, Cs, true),
-	    case mnesia_controller:get_network_copy(Tab, Cs) of
+	    case mnesia_controller:get_network_copy(Tid, Tab, Cs) of
 		{loaded, ok} ->
 		    {true, optional};
 		{not_loaded, ErrReason} ->
@@ -1993,28 +1953,11 @@ prepare_op(Tid, {op, add_table_copy, Storage, Node, TabDef}, _WaitFor) ->
 	    {true, optional}
     end;
 
-prepare_op(Tid, {op, del_table_copy, _Storage, Node, TabDef}, _WaitFor) ->
+prepare_op(_Tid, {op, del_table_copy, _Storage, Node, TabDef}, _WaitFor) ->
     Cs = list2cs(TabDef),
     Tab = Cs#cstruct.name,
-
-    if
-	%% Schema table lock is always required to run a schema op.
-	%% No need to look it.
-	node(Tid#tid.pid) == node(), Tab /= schema ->
-	    Self = self(),
-	    Pid = spawn_link(fun() -> lock_del_table(Tab, Node, Cs, Self) end),
-	    put(mnesia_lock, Pid),
-	    receive
-		{Pid, updated} ->
-		    {true, optional};
-		{Pid, FailReason} ->
-		    mnesia:abort(FailReason);
-		{'EXIT', Pid, Reason} ->
-		    mnesia:abort(Reason)
-	    end;
-	true ->
-	    {true, optional}
-    end;
+    set_where_to_read(Tab, Node, Cs),
+    {true, optional};
 
 prepare_op(_Tid, {op, change_table_copy_type,  N, FromS, ToS, TabDef}, _WaitFor)
   when N == node() ->
@@ -2228,46 +2171,6 @@ receive_sync(Nodes, Pids) ->
 	    {abort, Else}
     end.
 
-lock_del_table(Tab, NewNode, Cs0, Father) ->
-    Ns = val({schema, active_replicas}),
-    process_flag(trap_exit,true),
-    Lock = fun() ->
-		   mnesia:write_lock_table(Tab),
-		   %% Sigh using cs record
-		   Set = fun(Node) ->
-				 [Cs] = normalize_cs([Cs0], Node),
-				 rpc:call(Node, ?MODULE, set_where_to_read, [Tab, NewNode, Cs])
-			 end,
-		   Res = [Set(Node) || Node <- Ns],
-		   Filter = fun(ok) ->
-				    false;
-			       ({badrpc, {'EXIT', {undef, _}}}) ->
-				    %% This will be the case we talks with elder nodes
-				    %% than 3.8.2, they will set where_to_read without
-				    %% getting a lock.
-				    false;
-			       (_) ->
-				    true
-			    end,
-		   case lists:filter(Filter, Res) of
-		       [] ->
-			   Father ! {self(), updated},
-			   %% When transaction is commited the process dies
-			   %% and the lock is released.
-			   receive _ -> ok end;
-		       Err ->
-			   Father ! {self(), {bad_commit, Err}}
-		   end,
-		   ok
-	   end,
-    case mnesia:transaction(Lock) of
-	{atomic, ok} ->  ok;
-	{aborted, R} ->  Father ! {self(), R}
-    end,
-    unlink(Father),
-    unlink(whereis(mnesia_tm)),
-    exit(normal).
-
 set_where_to_read(Tab, Node, Cs) ->
     case mnesia_lib:val({Tab, where_to_read}) of
 	Node ->
@@ -2418,13 +2321,19 @@ undo_prepare_op(Tid, {op, add_table_copy, Storage, Node, TabDef}) ->
 	    insert_cstruct(Tid, Cs2, true) % Don't care about the version
     end;
 
-undo_prepare_op(_Tid, {op, del_table_copy, _, Node, TabDef})
-  when Node == node() ->
-    WriteLocker = get(mnesia_lock),
-    WriteLocker =/= undefined andalso (WriteLocker ! die),
+undo_prepare_op(_Tid, {op, del_table_copy, _, Node, TabDef}) ->
     Cs = list2cs(TabDef),
     Tab = Cs#cstruct.name,
-    mnesia_lib:set({Tab, where_to_read}, Node);
+    if node() =:= Node ->
+	    mnesia_lib:set({Tab, where_to_read}, Node);
+       true ->
+	    case mnesia_lib:val({Tab, where_to_read}) of
+		nowhere ->
+		    mnesia_lib:set_remote_where_to_read(Tab);
+		_ ->
+		    ignore
+	    end
+    end;
 
 undo_prepare_op(_Tid, {op, change_table_copy_type, N, FromS, ToS, TabDef})
         when N == node() ->
@@ -2885,40 +2794,11 @@ do_merge_schema(LockTabs0) ->
     end.
 
 fetch_cstructs(Node) ->
-    case need_old_cstructs([Node]) of
-	false ->
-	    rpc:call(Node, mnesia_controller, get_remote_cstructs, []);
-	_Ver ->
-	    case rpc:call(Node, mnesia_controller, get_cstructs, []) of
-		{cstructs, Cs0, RR} ->
-		    {cstructs, [list2cs(cs2list(Cs)) || Cs <- Cs0], RR};
-		Err -> Err
-	    end
-    end.
+    rpc:call(Node, mnesia_controller, get_remote_cstructs, []).
 
-need_old_cstructs() ->
-    need_old_cstructs(val({schema, where_to_write})).
-
-need_old_cstructs(Nodes) ->
-    Filter = fun(Node) -> not mnesia_monitor:needs_protocol_conversion(Node) end,
-    case lists:dropwhile(Filter, Nodes) of
-	[] -> false;
-	[Node|_] ->
-	    case rpc:call(Node, mnesia_lib, val, [{schema,cstruct}]) of
-		#cstruct{} ->
-		    %% mnesia_lib:warning("Mnesia on ~p do not need to convert cstruct (~p)~n",
-		    %% 		       [node(), Node]),
-		    false;
-		{badrpc, _} ->
-		    need_old_cstructs(lists:delete(Node,Nodes));
-		Cs when element(1, Cs) == cstruct, tuple_size(Cs) == 17 ->
-		    ver4_4_18;			% Without majority
-		Cs when element(1, Cs) == cstruct, tuple_size(Cs) == 18 ->
-		    ver4_4_19;			% With majority
-		Cs when element(1, Cs) == cstruct, tuple_size(Cs) == 19 ->
-		    ver4_6			% With storage_properties
-	    end
-    end.
+need_old_cstructs() -> false.
+
+need_old_cstructs(_Nodes) -> false.
 
 tab_to_nodes(Tab) when is_atom(Tab) ->
     Cs = val({Tab, cstruct}),
diff --git a/lib/mnesia/test/mnesia_isolation_test.erl b/lib/mnesia/test/mnesia_isolation_test.erl
index b66da6e390..4dd0c01d05 100644
--- a/lib/mnesia/test/mnesia_isolation_test.erl
+++ b/lib/mnesia/test/mnesia_isolation_test.erl
@@ -39,7 +39,7 @@ groups() ->
     [{locking, [],
       [no_conflict, simple_queue_conflict,
        advanced_queue_conflict, simple_deadlock_conflict,
-       advanced_deadlock_conflict, lock_burst,
+       advanced_deadlock_conflict, schema_deadlock, lock_burst,
        {group, sticky_locks}, {group, unbound_locking},
        {group, admin_conflict}, nasty]},
      {sticky_locks, [], [basic_sticky_functionality]},
@@ -148,20 +148,32 @@ simple_queue_conflict(Config) when is_list(Config) ->
     fun_loop(Fun, AllSharedLocks, OneExclusiveLocks), 
     ok.
 
-wait_for_lock(Pid, _Nodes, 0) ->
+wait_for_lock(Pid, Nodes, Retry) ->
+    wait_for_lock(Pid, Nodes, Retry, queue).
+
+wait_for_lock(Pid, _Nodes, 0, queue) ->
     Queue = mnesia:system_info(lock_queue),
     ?error("Timeout while waiting for lock on Pid ~p in queue ~p~n", [Pid, Queue]);
-wait_for_lock(Pid, Nodes, N) ->
-    rpc:multicall(Nodes, sys, get_status, [mnesia_locker]), 
-    List = [rpc:call(Node, mnesia, system_info, [lock_queue]) || Node <- Nodes],
+wait_for_lock(Pid, _Nodes, 0, held) ->
+    Held = mnesia:system_info(held_locks),
+    ?error("Timeout while waiting for lock on Pid ~p (held) ~p~n", [Pid, Held]);
+wait_for_lock(Pid, Nodes, N, Where) ->
+    rpc:multicall(Nodes, sys, get_status, [mnesia_locker]),
+    List = case Where of
+	       queue ->
+		   [rpc:call(Node, mnesia, system_info, [lock_queue]) || Node <- Nodes];
+	       held ->
+		   [rpc:call(Node, mnesia, system_info, [held_locks]) || Node <- Nodes]
+           end,
     Q = lists:append(List),
-    check_q(Pid, Q, Nodes, N).
+    check_q(Pid, Q, Nodes, N, Where).
 
-check_q(Pid, [{_Oid, _Op, Pid, _Tid, _WFT} | _Tail], _N, _Count) -> ok;
-check_q(Pid, [_ | Tail], N, Count) -> check_q(Pid, Tail, N, Count);
-check_q(Pid, [], N, Count) ->
-    timer:sleep(500),
-    wait_for_lock(Pid, N, Count - 1).
+check_q(Pid, [{_Oid, _Op, Pid, _Tid, _WFT} | _Tail], _N, _Count, _Where) -> ok;
+check_q(Pid, [{_Oid, _Op, {tid,_,Pid}} | _Tail], _N, _Count, _Where) -> ok;
+check_q(Pid, [_ | Tail], N, Count, Where) -> check_q(Pid, Tail, N, Count, Where);
+check_q(Pid, [], N, Count, Where) ->
+    timer:sleep(200),
+    wait_for_lock(Pid, N, Count - 1, Where).
 
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@@ -270,6 +282,43 @@ advanced_deadlock_conflict(Config) when is_list(Config) ->
     ?match([], mnesia:system_info(lock_queue)), 
     ok.
 
+%%  Verify (and regression test) deadlock in del_table_copy(schema, Node)
+schema_deadlock(Config) when is_list(Config) ->
+    Ns = [Node1, Node2] = ?acquire_nodes(2, Config),
+    ?match({atomic, ok}, mnesia:create_table(a, [{disc_copies, Ns}])),
+    ?match({atomic, ok}, mnesia:create_table(b, [{disc_copies, Ns}])),
+
+    Tester = self(),
+
+    Deadlocker = fun() ->
+			 mnesia:write({a,1,1}),  %% grab write lock on A
+			 receive
+			     continue ->
+				 mnesia:write({b,1,1}), %% grab write lock on B
+				 end_trans
+			 end
+		 end,
+
+    ?match(stopped, rpc:call(Node2, mnesia, stop, [])),
+    timer:sleep(500), %% Let Node1 reconfigure
+    sys:get_status(mnesia_monitor),
+
+    DoingTrans = spawn_link(fun() ->  Tester ! {self(),mnesia:transaction(Deadlocker)} end),
+    wait_for_lock(DoingTrans, [Node1], 10, held),
+    %% Will grab write locks on schema, a, and b
+    DoingSchema = spawn_link(fun() -> Tester ! {self(), mnesia:del_table_copy(schema, Node2)} end),
+    timer:sleep(500), %% Let schema trans start, and try to grab locks
+    DoingTrans ! continue,
+
+    ?match(ok, receive {DoingTrans,  {atomic, end_trans}} -> ok after 5000 -> timeout end),
+    ?match(ok, receive {DoingSchema,  {atomic, ok}} -> ok after 5000 -> timeout end),
+
+    sys:get_status(whereis(mnesia_locker)), % Explicit sync, release locks is async
+    ?match([], mnesia:system_info(held_locks)),
+    ?match([], mnesia:system_info(lock_queue)),
+    ok.
+
+
 one_oid(Tab) -> {Tab, 1}.
 other_oid(Tab) -> {Tab, 2}.