From a6d87854c3ae65dba8dba6571b4d31d901316a39 Mon Sep 17 00:00:00 2001
From: Sverker Eriksson <sverker@erlang.org>
Date: Fri, 8 Jul 2016 15:13:35 +0200
Subject: erts: Fix deadlock in ets:update_counter/4

in 'set' with 'write_concurrency'
when inserting default object causes table to grow
and the bucket to split is protected by same lock as the key.
---
 erts/emulator/beam/erl_db_hash.c | 34 ++++++++++++++++++----------------
 erts/emulator/beam/erl_db_util.h |  1 +
 2 files changed, 19 insertions(+), 16 deletions(-)

(limited to 'erts')

diff --git a/erts/emulator/beam/erl_db_hash.c b/erts/emulator/beam/erl_db_hash.c
index 6b23be1adf..12ae086b31 100644
--- a/erts/emulator/beam/erl_db_hash.c
+++ b/erts/emulator/beam/erl_db_hash.c
@@ -2866,15 +2866,7 @@ db_lookup_dbterm_hash(Process *p, DbTable *tbl, Eterm key, Eterm obj,
             q->hvalue = hval;
             q->next = NULL;
             *bp = b = q;
-
-            {
-                int nitems = erts_smp_atomic_inc_read_nob(&tb->common.nitems);
-                int nactive = NACTIVE(tb);
-
-                if (nitems > nactive * (CHAIN_LEN + 1) && !IS_FIXED(tb)) {
-                    grow(tb, nactive);
-                }
-            }
+            flags |= DB_INC_TRY_GROW;
         } else {
             HashDbTerm *q, *next = b->next;
 
@@ -2928,13 +2920,23 @@ db_finalize_dbterm_hash(int cret, DbUpdateHandle* handle)
         WUNLOCK_HASH(lck);
         erts_smp_atomic_dec_nob(&tb->common.nitems);
         try_shrink(tb);
-    } else if (handle->flags & DB_MUST_RESIZE) {
-	db_finalize_resize(handle, offsetof(HashDbTerm,dbterm));
-	WUNLOCK_HASH(lck);
-        free_me = b;
-    }
-    else {
-	WUNLOCK_HASH(lck);
+    } else {
+        if (handle->flags & DB_MUST_RESIZE) {
+            db_finalize_resize(handle, offsetof(HashDbTerm,dbterm));
+            free_me = b;
+        }
+        if (handle->flags & DB_INC_TRY_GROW) {
+            int nactive;
+            int nitems = erts_smp_atomic_inc_read_nob(&tb->common.nitems);
+            WUNLOCK_HASH(lck);
+            nactive = NACTIVE(tb);
+
+            if (nitems > nactive * (CHAIN_LEN + 1) && !IS_FIXED(tb)) {
+                grow(tb, nactive);
+            }
+        } else {
+            WUNLOCK_HASH(lck);
+        }
     }
 
     if (free_me)
diff --git a/erts/emulator/beam/erl_db_util.h b/erts/emulator/beam/erl_db_util.h
index 60f7067d70..4acedbfed0 100644
--- a/erts/emulator/beam/erl_db_util.h
+++ b/erts/emulator/beam/erl_db_util.h
@@ -79,6 +79,7 @@ typedef union db_table DbTable;
 
 #define DB_MUST_RESIZE 1
 #define DB_NEW_OBJECT 2
+#define DB_INC_TRY_GROW 4
 
 /* Info about a database entry while it's being updated
  * (by update_counter or update_element)
-- 
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