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

1 files changed, 19 insertions, 1 deletions

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);