diff --git a/mdbx.h b/mdbx.h
index 768e9b00..de16ccff 100644
--- a/mdbx.h
+++ b/mdbx.h
@@ -5570,7 +5570,7 @@ LIBMDBX_API int mdbx_txn_lock(MDBX_env *env, bool dont_wait);
 /** \brief Releases write-transaction lock.
  * Provided for custom and/or complex locking scenarios.
  * \returns A non-zero error value on failure and 0 on success. */
-LIBMDBX_API void mdbx_txn_unlock(MDBX_env *env);
+LIBMDBX_API int mdbx_txn_unlock(MDBX_env *env);
 
 /** \brief Open an environment instance using specific meta-page
  * for checking and recovery.
diff --git a/src/core.c b/src/core.c
index 899b65af..d0cb0914 100644
--- a/src/core.c
+++ b/src/core.c
@@ -8200,7 +8200,7 @@ retry:;
         rc = MDBX_SUCCESS /* means "some data was synced" */;
       }
 
-      err = mdbx_txn_lock(env, nonblock);
+      err = osal_txn_lock(env, nonblock);
       if (unlikely(err != MDBX_SUCCESS))
         return err;
 
@@ -8247,7 +8247,7 @@ retry:;
 
 bailout:
   if (locked)
-    mdbx_txn_unlock(env);
+    osal_txn_unlock(env);
   return rc;
 }
 
@@ -8442,7 +8442,7 @@ static void txn_valgrind(MDBX_env *env, MDBX_txn *txn) {
     } else if (env->me_flags & MDBX_RDONLY) {
       /* read-only mode, no write-txn, no wlock mutex */
       last = NUM_METAS;
-    } else if (mdbx_txn_lock(env, true) == MDBX_SUCCESS) {
+    } else if (osal_txn_lock(env, true) == MDBX_SUCCESS) {
       /* no write-txn */
       last = NUM_METAS;
       should_unlock = true;
@@ -8463,7 +8463,7 @@ static void txn_valgrind(MDBX_env *env, MDBX_txn *txn) {
           pgno2bytes(env, edge - last));
     }
     if (should_unlock)
-      mdbx_txn_unlock(env);
+      osal_txn_unlock(env);
   }
 }
 #endif /* MDBX_USE_VALGRIND || __SANITIZE_ADDRESS__ */
@@ -8840,6 +8840,7 @@ static int txn_renew(MDBX_txn *txn, const unsigned flags) {
       txn->mt_flags = MDBX_TXN_RDONLY | MDBX_TXN_FINISHED;
       return MDBX_SUCCESS;
     }
+    txn->mt_owner = tid;
 
     /* Seek & fetch the last meta */
     uint64_t timestamp = 0;
@@ -8915,12 +8916,11 @@ static int txn_renew(MDBX_txn *txn, const unsigned flags) {
       rc = MDBX_CORRUPTED;
       goto bailout;
     }
-    eASSERT(env, txn->mt_txnid >= env->me_lck->mti_oldest_reader.weak);
     txn->mt_dbxs = env->me_dbxs; /* mostly static anyway */
+    txn->mt_numdbs = env->me_numdbs;
     ENSURE(env, txn->mt_txnid >=
                     /* paranoia is appropriate here */ env->me_lck
                         ->mti_oldest_reader.weak);
-    txn->mt_numdbs = env->me_numdbs;
   } else {
     eASSERT(env, (flags & ~(MDBX_TXN_RW_BEGIN_FLAGS | MDBX_TXN_SPILLS |
                             MDBX_WRITEMAP)) == 0);
@@ -8946,16 +8946,16 @@ static int txn_renew(MDBX_txn *txn, const unsigned flags) {
 
     /* Not yet touching txn == env->me_txn0, it may be active */
     jitter4testing(false);
-    rc = mdbx_txn_lock(env, !!(flags & MDBX_TXN_TRY));
+    rc = osal_txn_lock(env, !!(flags & MDBX_TXN_TRY));
     if (unlikely(rc))
       return rc;
     if (unlikely(env->me_flags & MDBX_FATAL_ERROR)) {
-      mdbx_txn_unlock(env);
+      osal_txn_unlock(env);
       return MDBX_PANIC;
     }
 #if defined(_WIN32) || defined(_WIN64)
     if (unlikely(!env->me_map)) {
-      mdbx_txn_unlock(env);
+      osal_txn_unlock(env);
       return MDBX_EPERM;
     }
 #endif /* Windows */
@@ -9129,7 +9129,6 @@ static int txn_renew(MDBX_txn *txn, const unsigned flags) {
 #if defined(MDBX_USE_VALGRIND) || defined(__SANITIZE_ADDRESS__)
     txn_valgrind(env, txn);
 #endif /* MDBX_USE_VALGRIND || __SANITIZE_ADDRESS__ */
-    txn->mt_owner = tid;
     return MDBX_SUCCESS;
   }
 bailout:
@@ -9810,9 +9809,7 @@ static int txn_end(MDBX_txn *txn, const unsigned mode) {
                 txn->mt_txnid == slot->mr_txnid.weak &&
                     slot->mr_txnid.weak >= env->me_lck->mti_oldest_reader.weak);
 #if defined(MDBX_USE_VALGRIND) || defined(__SANITIZE_ADDRESS__)
-        atomic_add32(&env->me_ignore_EDEADLK, 1);
         txn_valgrind(env, nullptr);
-        atomic_sub32(&env->me_ignore_EDEADLK, 1);
 #endif /* MDBX_USE_VALGRIND || __SANITIZE_ADDRESS__ */
         atomic_store32(&slot->mr_snapshot_pages_used, 0, mo_Relaxed);
         safe64_reset(&slot->mr_txnid, false);
@@ -9845,7 +9842,6 @@ static int txn_end(MDBX_txn *txn, const unsigned mode) {
 #endif /* MDBX_USE_VALGRIND || __SANITIZE_ADDRESS__ */
 
     txn->mt_flags = MDBX_TXN_FINISHED;
-    txn->mt_owner = 0;
     env->me_txn = txn->mt_parent;
     pnl_free(txn->tw.spilled.list);
     txn->tw.spilled.list = nullptr;
@@ -9858,7 +9854,7 @@ static int txn_end(MDBX_txn *txn, const unsigned mode) {
       if (!(env->me_flags & MDBX_WRITEMAP))
         dlist_free(txn);
       /* The writer mutex was locked in mdbx_txn_begin. */
-      mdbx_txn_unlock(env);
+      osal_txn_unlock(env);
     } else {
       eASSERT(env, txn->mt_parent != NULL);
       MDBX_txn *const parent = txn->mt_parent;
@@ -9870,6 +9866,7 @@ static int txn_end(MDBX_txn *txn, const unsigned mode) {
       eASSERT(env, memcmp(&txn->tw.troika, &parent->tw.troika,
                           sizeof(meta_troika_t)) == 0);
 
+      txn->mt_owner = 0;
       if (txn->tw.lifo_reclaimed) {
         eASSERT(env, MDBX_PNL_GETSIZE(txn->tw.lifo_reclaimed) >=
                          (uintptr_t)parent->tw.lifo_reclaimed);
@@ -13258,7 +13255,7 @@ __cold int mdbx_env_set_geometry(MDBX_env *env, intptr_t size_lower,
       return MDBX_EACCESS;
 
     if (!inside_txn) {
-      int err = mdbx_txn_lock(env, false);
+      int err = osal_txn_lock(env, false);
       if (unlikely(err != MDBX_SUCCESS))
         return err;
       need_unlock = true;
@@ -13609,7 +13606,7 @@ __cold int mdbx_env_set_geometry(MDBX_env *env, intptr_t size_lower,
 
 bailout:
   if (need_unlock)
-    mdbx_txn_unlock(env);
+    osal_txn_unlock(env);
   return rc;
 }
 
@@ -21675,13 +21672,13 @@ __cold static int env_copy_asis(MDBX_env *env, MDBX_txn *read_txn,
     return rc;
 
   /* Temporarily block writers until we snapshot the meta pages */
-  rc = mdbx_txn_lock(env, false);
+  rc = osal_txn_lock(env, false);
   if (unlikely(rc != MDBX_SUCCESS))
     return rc;
 
   rc = txn_renew(read_txn, MDBX_TXN_RDONLY);
   if (unlikely(rc != MDBX_SUCCESS)) {
-    mdbx_txn_unlock(env);
+    osal_txn_unlock(env);
     return rc;
   }
 
@@ -21693,7 +21690,7 @@ __cold static int env_copy_asis(MDBX_env *env, MDBX_txn *read_txn,
   memcpy(buffer, env->me_map, meta_bytes);
   MDBX_meta *const headcopy = /* LY: get pointer to the snapshot copy */
       ptr_disp(buffer, ptr_dist(meta_recent(env, &troika).ptr_c, env->me_map));
-  mdbx_txn_unlock(env);
+  osal_txn_unlock(env);
 
   if (flags & MDBX_CP_FORCE_DYNAMIC_SIZE)
     meta_make_sizeable(headcopy);
@@ -21953,7 +21950,7 @@ __cold int mdbx_env_set_flags(MDBX_env *env, MDBX_env_flags_t flags,
                            env->me_txn0->mt_owner != osal_thread_self();
   bool should_unlock = false;
   if (lock_needed) {
-    rc = mdbx_txn_lock(env, false);
+    rc = osal_txn_lock(env, false);
     if (unlikely(rc))
       return rc;
     should_unlock = true;
@@ -21965,7 +21962,7 @@ __cold int mdbx_env_set_flags(MDBX_env *env, MDBX_env_flags_t flags,
     env->me_flags &= ~flags;
 
   if (should_unlock)
-    mdbx_txn_unlock(env);
+    osal_txn_unlock(env);
   return MDBX_SUCCESS;
 }
 
@@ -24828,7 +24825,7 @@ __cold int mdbx_env_set_option(MDBX_env *env, const MDBX_option_t option,
       return MDBX_EINVAL;
     if (env->me_options.dp_reserve_limit != (unsigned)value) {
       if (lock_needed) {
-        err = mdbx_txn_lock(env, false);
+        err = osal_txn_lock(env, false);
         if (unlikely(err != MDBX_SUCCESS))
           return err;
         should_unlock = true;
@@ -24868,7 +24865,7 @@ __cold int mdbx_env_set_option(MDBX_env *env, const MDBX_option_t option,
     if (unlikely(env->me_flags & MDBX_RDONLY))
       return MDBX_EACCESS;
     if (lock_needed) {
-      err = mdbx_txn_lock(env, false);
+      err = osal_txn_lock(env, false);
       if (unlikely(err != MDBX_SUCCESS))
         return err;
       should_unlock = true;
@@ -24968,7 +24965,7 @@ __cold int mdbx_env_set_option(MDBX_env *env, const MDBX_option_t option,
   }
 
   if (should_unlock)
-    mdbx_txn_unlock(env);
+    osal_txn_unlock(env);
   return err;
 }
 
@@ -25490,6 +25487,39 @@ mdbx_key_from_int32(const int32_t i32) {
 
 #endif /* LIBMDBX_NO_EXPORTS_LEGACY_API */
 
+/*------------------------------------------------------------------------------
+ * Locking API */
+
+int mdbx_txn_lock(MDBX_env *env, bool dont_wait) {
+  int rc = check_env(env, true);
+  if (unlikely(rc != MDBX_SUCCESS))
+    return rc;
+
+  if (unlikely(env->me_flags & MDBX_RDONLY))
+    return MDBX_EACCESS;
+  if (unlikely(env->me_txn0->mt_owner ||
+               (env->me_txn0->mt_flags & MDBX_TXN_FINISHED) == 0))
+    return MDBX_BUSY;
+
+  return osal_txn_lock(env, dont_wait);
+}
+
+int mdbx_txn_unlock(MDBX_env *env) {
+  int rc = check_env(env, true);
+  if (unlikely(rc != MDBX_SUCCESS))
+    return rc;
+
+  if (unlikely(env->me_flags & MDBX_RDONLY))
+    return MDBX_EACCESS;
+  if (unlikely(env->me_txn0->mt_owner != osal_thread_self()))
+    return MDBX_THREAD_MISMATCH;
+  if (unlikely((env->me_txn0->mt_flags & MDBX_TXN_FINISHED) == 0))
+    return MDBX_BUSY;
+
+  osal_txn_unlock(env);
+  return MDBX_SUCCESS;
+}
+
 /******************************************************************************/
 /* *INDENT-OFF* */
 /* clang-format off */
diff --git a/src/internals.h b/src/internals.h
index 3d1fd706..1664dcd7 100644
--- a/src/internals.h
+++ b/src/internals.h
@@ -1482,7 +1482,6 @@ struct MDBX_env {
   int me_valgrind_handle;
 #endif
 #if defined(MDBX_USE_VALGRIND) || defined(__SANITIZE_ADDRESS__)
-  MDBX_atomic_uint32_t me_ignore_EDEADLK;
   pgno_t me_poison_edge;
 #endif /* MDBX_USE_VALGRIND || __SANITIZE_ADDRESS__ */
 
diff --git a/src/lck-posix.c b/src/lck-posix.c
index 17c50ddd..7f58e9ed 100644
--- a/src/lck-posix.c
+++ b/src/lck-posix.c
@@ -120,7 +120,7 @@ mdbx_global_destructor(void) {
  *  - Блокировка таблицы читателей для регистрации,
  *    т.е. функции osal_rdt_lock() и osal_rdt_unlock().
  *  - Блокировка БД для пишущих транзакций,
- *    т.е. функции mdbx_txn_lock() и mdbx_txn_unlock().
+ *    т.е. функции osal_txn_lock() и osal_txn_unlock().
  *
  * Остальной функционал реализуется отдельно посредством файловых блокировок:
  *  - Первоначальный захват БД в режиме exclusive/shared и последующий перевод
@@ -527,6 +527,34 @@ MDBX_INTERNAL_FUNC int osal_lck_downgrade(MDBX_env *env) {
   return rc;
 }
 
+MDBX_INTERNAL_FUNC int osal_lck_upgrade(MDBX_env *env, bool dont_wait) {
+  assert(env->me_lfd != INVALID_HANDLE_VALUE);
+  if (unlikely(osal_getpid() != env->me_pid))
+    return MDBX_PANIC;
+
+  const int cmd = dont_wait ? op_setlk : op_setlkw;
+  int rc = lck_op(env->me_lfd, cmd, F_WRLCK, 0, 1);
+  if (rc == MDBX_SUCCESS && (env->me_flags & MDBX_EXCLUSIVE) == 0) {
+    rc = (env->me_pid > 1)
+             ? lck_op(env->me_lazy_fd, cmd, F_WRLCK, 0, env->me_pid - 1)
+             : MDBX_SUCCESS;
+    if (rc == MDBX_SUCCESS) {
+      rc = lck_op(env->me_lazy_fd, cmd, F_WRLCK, env->me_pid + 1,
+                  OFF_T_MAX - env->me_pid - 1);
+      if (rc != MDBX_SUCCESS && env->me_pid > 1 &&
+          lck_op(env->me_lazy_fd, op_setlk, F_UNLCK, 0, env->me_pid - 1))
+        rc = MDBX_PANIC;
+    }
+    if (rc != MDBX_SUCCESS && lck_op(env->me_lfd, op_setlk, F_RDLCK, 0, 1))
+      rc = MDBX_PANIC;
+  }
+  if (unlikely(rc != 0)) {
+    ERROR("%s, err %u", "lck", rc);
+    assert(MDBX_IS_ERROR(rc));
+  }
+  return rc;
+}
+
 __cold MDBX_INTERNAL_FUNC int osal_lck_destroy(MDBX_env *env,
                                                MDBX_env *inprocess_neighbor) {
   if (unlikely(osal_getpid() != env->me_pid))
@@ -822,11 +850,6 @@ __cold static int mdbx_ipclock_failed(MDBX_env *env, osal_ipclock_t *ipc,
 #error "FIXME"
 #endif /* MDBX_LOCKING */
 
-#if defined(MDBX_USE_VALGRIND) || defined(__SANITIZE_ADDRESS__)
-  if (rc == EDEADLK && atomic_load32(&env->me_ignore_EDEADLK, mo_Relaxed) > 0)
-    return rc;
-#endif /* MDBX_USE_VALGRIND || __SANITIZE_ADDRESS__ */
-
   ERROR("mutex (un)lock failed, %s", mdbx_strerror(err));
   if (rc != EDEADLK)
     env->me_flags |= MDBX_FATAL_ERROR;
@@ -931,20 +954,28 @@ MDBX_INTERNAL_FUNC void osal_rdt_unlock(MDBX_env *env) {
   jitter4testing(true);
 }
 
-int mdbx_txn_lock(MDBX_env *env, bool dont_wait) {
+int osal_txn_lock(MDBX_env *env, bool dont_wait) {
   TRACE("%swait %s", dont_wait ? "dont-" : "", ">>");
+  eASSERT(env, !env->me_txn0->mt_owner);
   jitter4testing(true);
-  int rc = mdbx_ipclock_lock(env, &env->me_lck->mti_wlock, dont_wait);
-  TRACE("<< rc %d", rc);
-  return MDBX_IS_ERROR(rc) ? rc : MDBX_SUCCESS;
+  const int err = mdbx_ipclock_lock(env, &env->me_lck->mti_wlock, dont_wait);
+  int rc = err;
+  if (likely(!MDBX_IS_ERROR(err))) {
+    env->me_txn0->mt_owner = osal_thread_self();
+    rc = MDBX_SUCCESS;
+  }
+  TRACE("<< rc %d", err);
+  return rc;
 }
 
-void mdbx_txn_unlock(MDBX_env *env) {
+void osal_txn_unlock(MDBX_env *env) {
   TRACE("%s", ">>");
-  int rc = mdbx_ipclock_unlock(env, &env->me_lck->mti_wlock);
-  TRACE("<< rc %d", rc);
-  if (unlikely(rc != MDBX_SUCCESS))
-    mdbx_panic("%s() failed: err %d\n", __func__, rc);
+  eASSERT(env, env->me_txn0->mt_owner == osal_thread_self());
+  env->me_txn0->mt_owner = 0;
+  int err = mdbx_ipclock_unlock(env, &env->me_lck->mti_wlock);
+  TRACE("<< err %d", err);
+  if (unlikely(err != MDBX_SUCCESS))
+    mdbx_panic("%s() failed: err %d\n", __func__, err);
   jitter4testing(true);
 }
 
diff --git a/src/lck-windows.c b/src/lck-windows.c
index 8ffccb1b..ed77da30 100644
--- a/src/lck-windows.c
+++ b/src/lck-windows.c
@@ -178,7 +178,8 @@ static int funlock(mdbx_filehandle_t fd, size_t offset, size_t bytes) {
 #define DXB_BODY (env->me_psize * (size_t)NUM_METAS), DXB_MAXLEN
 #define DXB_WHOLE 0, DXB_MAXLEN
 
-int mdbx_txn_lock(MDBX_env *env, bool dontwait) {
+int osal_txn_lock(MDBX_env *env, bool dontwait) {
+  eASSERT(env, !env->me_txn0->mt_owner);
   if (dontwait) {
     if (!TryEnterCriticalSection(&env->me_windowsbug_lock))
       return MDBX_BUSY;
@@ -194,12 +195,8 @@ int mdbx_txn_lock(MDBX_env *env, bool dontwait) {
     }
   }
 
-  if (env->me_flags & MDBX_EXCLUSIVE) {
-    /* Zap: Failing to release lock 'env->me_windowsbug_lock'
-     *      in function 'mdbx_txn_lock' */
-    MDBX_SUPPRESS_GOOFY_MSVC_ANALYZER(26115);
-    return MDBX_SUCCESS;
-  }
+  if (env->me_flags & MDBX_EXCLUSIVE)
+    goto done;
 
   const HANDLE fd4data =
       env->me_overlapped_fd ? env->me_overlapped_fd : env->me_lazy_fd;
@@ -218,17 +215,20 @@ int mdbx_txn_lock(MDBX_env *env, bool dontwait) {
     }
   }
   if (rc == MDBX_SUCCESS) {
+  done:
     /* Zap: Failing to release lock 'env->me_windowsbug_lock'
      *      in function 'mdbx_txn_lock' */
     MDBX_SUPPRESS_GOOFY_MSVC_ANALYZER(26115);
-    return rc;
+    env->me_txn0->mt_owner = osal_thread_self();
+    return MDBX_SUCCESS;
   }
 
   LeaveCriticalSection(&env->me_windowsbug_lock);
   return (!dontwait || rc != ERROR_LOCK_VIOLATION) ? rc : MDBX_BUSY;
 }
 
-void mdbx_txn_unlock(MDBX_env *env) {
+void osal_txn_unlock(MDBX_env *env) {
+  eASSERT(env, env->me_txn0->mt_owner == osal_thread_self());
   if ((env->me_flags & MDBX_EXCLUSIVE) == 0) {
     const HANDLE fd4data =
         env->me_overlapped_fd ? env->me_overlapped_fd : env->me_lazy_fd;
@@ -236,6 +236,7 @@ void mdbx_txn_unlock(MDBX_env *env) {
     if (err != MDBX_SUCCESS)
       mdbx_panic("%s failed: err %u", __func__, err);
   }
+  env->me_txn0->mt_owner = 0;
   LeaveCriticalSection(&env->me_windowsbug_lock);
 }
 
@@ -442,7 +443,7 @@ osal_resume_threads_after_remap(mdbx_handle_array_t *array) {
  *  The osal_lck_downgrade() moves the locking-FSM from "exclusive write"
  *  state to the "used" (i.e. shared) state.
  *
- *  The mdbx_lck_upgrade() moves the locking-FSM from "used" (i.e. shared)
+ *  The osal_lck_upgrade() moves the locking-FSM from "used" (i.e. shared)
  *  state to the "exclusive write" state.
  */
 
@@ -615,7 +616,7 @@ MDBX_INTERNAL_FUNC int osal_lck_downgrade(MDBX_env *env) {
   return MDBX_SUCCESS /* 5) now at S-? (used), done */;
 }
 
-MDBX_INTERNAL_FUNC int mdbx_lck_upgrade(MDBX_env *env) {
+MDBX_INTERNAL_FUNC int osal_lck_upgrade(MDBX_env *env, bool dont_wait) {
   /* Transite from used state (S-?) to exclusive-write (E-E) */
   assert(env->me_lfd != INVALID_HANDLE_VALUE);
 
@@ -625,7 +626,9 @@ MDBX_INTERNAL_FUNC int mdbx_lck_upgrade(MDBX_env *env) {
 
   /* 1) now on S-? (used), try S-E (locked) */
   jitter4testing(false);
-  int rc = flock(env->me_lfd, LCK_EXCLUSIVE | LCK_DONTWAIT, LCK_UPPER);
+  int rc = flock(env->me_lfd,
+                 dont_wait ? LCK_EXCLUSIVE | LCK_DONTWAIT : LCK_EXCLUSIVE,
+                 LCK_UPPER);
   if (rc != MDBX_SUCCESS) {
     /* 2) something went wrong, give up */;
     VERBOSE("%s, err %u", "S-?(used) >> S-E(locked)", rc);
@@ -640,7 +643,9 @@ MDBX_INTERNAL_FUNC int mdbx_lck_upgrade(MDBX_env *env) {
 
   /* 4) now on ?-E (middle), try E-E (exclusive-write) */
   jitter4testing(false);
-  rc = flock(env->me_lfd, LCK_EXCLUSIVE | LCK_DONTWAIT, LCK_LOWER);
+  rc = flock(env->me_lfd,
+             dont_wait ? LCK_EXCLUSIVE | LCK_DONTWAIT : LCK_EXCLUSIVE,
+             LCK_LOWER);
   if (rc != MDBX_SUCCESS) {
     /* 5) something went wrong, give up */;
     VERBOSE("%s, err %u", "?-E(middle) >> E-E(exclusive-write)", rc);
@@ -686,7 +691,7 @@ MDBX_INTERNAL_FUNC int osal_lck_destroy(MDBX_env *env,
     const bool synced = env->me_lck_mmap.lck->mti_unsynced_pages.weak == 0;
     osal_munmap(&env->me_lck_mmap);
     if (synced && !inprocess_neighbor && env->me_lfd != INVALID_HANDLE_VALUE &&
-        mdbx_lck_upgrade(env) == MDBX_SUCCESS)
+        osal_lck_upgrade(env, true) == MDBX_SUCCESS)
       /* this will fail if LCK is used/mmapped by other process(es) */
       osal_ftruncate(env->me_lfd, 0);
   }
diff --git a/src/osal.h b/src/osal.h
index 3d45da4b..1b5c317f 100644
--- a/src/osal.h
+++ b/src/osal.h
@@ -718,6 +718,8 @@ MDBX_INTERNAL_FUNC int osal_lck_seize(MDBX_env *env);
 ///   operational lock.
 /// \return Error code or zero on success
 MDBX_INTERNAL_FUNC int osal_lck_downgrade(MDBX_env *env);
+MDBX_MAYBE_UNUSED MDBX_INTERNAL_FUNC int osal_lck_upgrade(MDBX_env *env,
+                                                          bool dont_wait);
 
 /// \brief Locks LCK-file or/and table of readers for (de)registering.
 /// \return Error code or zero on success
@@ -726,16 +728,12 @@ MDBX_INTERNAL_FUNC int osal_rdt_lock(MDBX_env *env);
 /// \brief Unlocks LCK-file or/and table of readers after (de)registering.
 MDBX_INTERNAL_FUNC void osal_rdt_unlock(MDBX_env *env);
 
-/// \brief Acquires lock for DB change (on writing transaction start)
-///   Reading transactions will not be blocked.
-///   Declared as LIBMDBX_API because it is used in mdbx_chk.
+/// \brief Acquires write-transaction lock.
 /// \return Error code or zero on success
-LIBMDBX_API int mdbx_txn_lock(MDBX_env *env, bool dont_wait);
+MDBX_INTERNAL_FUNC int osal_txn_lock(MDBX_env *env, bool dont_wait);
 
-/// \brief Releases lock once DB changes is made (after writing transaction
-///   has finished).
-///   Declared as LIBMDBX_API because it is used in mdbx_chk.
-LIBMDBX_API void mdbx_txn_unlock(MDBX_env *env);
+/// \brief Releases write-transaction lock..
+MDBX_INTERNAL_FUNC void osal_txn_unlock(MDBX_env *env);
 
 /// \brief Sets alive-flag of reader presence (indicative lock) for PID of
 ///   the current process. The function does no more than needed for