From 6b5533338fe0ffdb4a24077f885e16bfdf1ef881 Mon Sep 17 00:00:00 2001
From: Leo Yuriev <leo@yuriev.ru>
Date: Thu, 11 Jan 2018 21:09:34 +0300
Subject: [PATCH] mdbx: prohibit recursive txn-begin by MDBX_BUSY.

Change-Id: I46f5159cec72df9c8aece07fbfb462682499a272
---
 src/mdbx.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/mdbx.c b/src/mdbx.c
index 4cb1645b..68eefa49 100644
--- a/src/mdbx.c
+++ b/src/mdbx.c
@@ -2775,12 +2775,16 @@ int mdbx_txn_begin(MDBX_env *env, MDBX_txn *parent, unsigned flags,
     size = env->me_maxdbs * (sizeof(MDBX_db) + sizeof(MDBX_cursor *) + 1);
     size += tsize = sizeof(MDBX_ntxn);
   } else if (flags & MDBX_RDONLY) {
+    if (env->me_txn0 && unlikely(env->me_txn0->mt_owner == mdbx_thread_self()))
+      return MDBX_BUSY;
     size = env->me_maxdbs * (sizeof(MDBX_db) + 1);
     size += tsize = sizeof(MDBX_txn);
   } else {
     /* Reuse preallocated write txn. However, do not touch it until
      * mdbx_txn_renew0() succeeds, since it currently may be active. */
     txn = env->me_txn0;
+    if (unlikely(txn->mt_owner == mdbx_thread_self()))
+      return MDBX_BUSY;
     goto renew;
   }
   if (unlikely((txn = calloc(1, size)) == NULL)) {