1 files changed, 50 insertions, 25 deletions
diff --git a/src/vdbe.c b/src/vdbe.c
index 97f5ae696..128e81bdf 100644
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -43,7 +43,7 @@
 ** in this file for details.  If in doubt, do not deviate from existing
 ** commenting and indentation practices when changing or adding code.
 **
-** $Id: vdbe.c,v 1.827 2009/03/18 10:33:02 danielk1977 Exp $
+** $Id: vdbe.c,v 1.828 2009/03/23 17:11:27 danielk1977 Exp $
 */
 #include "sqliteInt.h"
 #include "vdbeInt.h"
@@ -4371,33 +4371,58 @@ case OP_CreateTable: {          /* out2-prerelease */
 ** then runs the new virtual machine.  It is thus a re-entrant opcode.
 */
 case OP_ParseSchema: {
-  char *zSql;
   int iDb = pOp->p1;
-  const char *zMaster;
-  InitData initData;
-
   assert( iDb>=0 && iDb<db->nDb );
-  if( !pOp->p2 && !DbHasProperty(db, iDb, DB_SchemaLoaded) ){
-    break;
+
+  /* If pOp->p2 is 0, then this opcode is being executed to read a
+  ** single row, for example the row corresponding to a new index
+  ** created by this VDBE, from the sqlite_master table. It only
+  ** does this if the corresponding in-memory schema is currently
+  ** loaded. Otherwise, the new index definition can be loaded along
+  ** with the rest of the schema when it is required.
+  **
+  ** Although the mutex on the BtShared object that corresponds to
+  ** database iDb (the database containing the sqlite_master table
+  ** read by this instruction) is currently held, it is necessary to
+  ** obtain the mutexes on all attached databases before checking if
+  ** the schema of iDb is loaded. This is because, at the start of
+  ** the sqlite3_exec() call below, SQLite will invoke 
+  ** sqlite3BtreeEnterAll(). If all mutexes are not already held, the
+  ** iDb mutex may be temporarily released to avoid deadlock. If 
+  ** this happens, then some other thread may delete the in-memory 
+  ** schema of database iDb before the SQL statement runs. The schema
+  ** will not be reloaded becuase the db->init.busy flag is set. This
+  ** can result in a "no such table: sqlite_master" or "malformed
+  ** database schema" error being returned to the user.
+  */
+  assert( sqlite3BtreeHoldsMutex(db->aDb[iDb].pBt) );
+  sqlite3BtreeEnterAll(db);
+  if( pOp->p2 || DbHasProperty(db, iDb, DB_SchemaLoaded) ){
+    const char *zMaster = SCHEMA_TABLE(iDb);
+    char *zSql;
+    InitData initData;
+    initData.db = db;
+    initData.iDb = pOp->p1;
+    initData.pzErrMsg = &p->zErrMsg;
+    zSql = sqlite3MPrintf(db,
+       "SELECT name, rootpage, sql FROM '%q'.%s WHERE %s",
+       db->aDb[iDb].zName, zMaster, pOp->p4.z);
+    if( zSql==0 ){
+      rc = SQLITE_NOMEM;
+    }else{
+      (void)sqlite3SafetyOff(db);
+      assert( db->init.busy==0 );
+      db->init.busy = 1;
+      initData.rc = SQLITE_OK;
+      assert( !db->mallocFailed );
+      rc = sqlite3_exec(db, zSql, sqlite3InitCallback, &initData, 0);
+      if( rc==SQLITE_OK ) rc = initData.rc;
+      sqlite3DbFree(db, zSql);
+      db->init.busy = 0;
+      (void)sqlite3SafetyOn(db);
+    }
   }
-  zMaster = SCHEMA_TABLE(iDb);
-  initData.db = db;
-  initData.iDb = pOp->p1;
-  initData.pzErrMsg = &p->zErrMsg;
-  zSql = sqlite3MPrintf(db,
-     "SELECT name, rootpage, sql FROM '%q'.%s WHERE %s",
-     db->aDb[iDb].zName, zMaster, pOp->p4.z);
-  if( zSql==0 ) goto no_mem;
-  (void)sqlite3SafetyOff(db);
-  assert( db->init.busy==0 );
-  db->init.busy = 1;
-  initData.rc = SQLITE_OK;
-  assert( !db->mallocFailed );
-  rc = sqlite3_exec(db, zSql, sqlite3InitCallback, &initData, 0);
-  if( rc==SQLITE_OK ) rc = initData.rc;
-  sqlite3DbFree(db, zSql);
-  db->init.busy = 0;
-  (void)sqlite3SafetyOn(db);
+  sqlite3BtreeLeaveAll(db);
   if( rc==SQLITE_NOMEM ){
     goto no_mem;
   }