Index: src/os_unix.c
==================================================================
--- src/os_unix.c
+++ src/os_unix.c
@@ -712,10 +712,13 @@
 }
 #ifdef SQLITE_DEBUG
 static int unixMutexHeld(void) {
   return sqlite3_mutex_held(unixBigLock);
 }
+static int unixMutexNotheld(void) {
+  return sqlite3_mutex_notheld(unixBigLock);
+}
 #endif
 
 
 #ifdef SQLITE_HAVE_OS_TRACE
 /*
@@ -1247,11 +1250,11 @@
 }
 
 /*
 ** Close all file descriptors accumuated in the unixInodeInfo->pUnused list.
 */ 
-static void closePendingFds(unixFile *pFile){
+static void closePendingFdsUnsafe(unixFile *pFile){
   unixInodeInfo *pInode = pFile->pInode;
   UnixUnusedFd *p;
   UnixUnusedFd *pNext;
   for(p=pInode->pUnused; p; p=pNext){
     pNext = p->pNext;
@@ -1259,10 +1262,16 @@
     sqlite3_free(p);
     nUnusedFd--;
   }
   pInode->pUnused = 0;
 }
+
+static void closePendingFds(unixFile *pFile){
+  unixEnterMutex();
+  closePendingFdsUnsafe(pFile);
+  unixLeaveMutex();
+}
 
 /*
 ** Release a unixInodeInfo structure previously allocated by findInodeInfo().
 **
 ** The mutex entered using the unixEnterMutex() function must be held
@@ -1273,11 +1282,11 @@
   assert( unixMutexHeld() );
   if( ALWAYS(pInode) ){
     pInode->nRef--;
     if( pInode->nRef==0 ){
       assert( pInode->pShmNode==0 );
-      closePendingFds(pFile);
+      closePendingFdsUnsafe(pFile);
       if( pInode->pPrev ){
         assert( pInode->pPrev->pNext==pInode );
         pInode->pPrev->pNext = pInode->pNext;
       }else{
         assert( inodeList==pInode );
@@ -1456,10 +1465,11 @@
 
   SimulateIOError( return SQLITE_IOERR_CHECKRESERVEDLOCK; );
 
   assert( pFile );
   assert( pFile->eFileLock<=SHARED_LOCK );
+  assert( unixMutexNotheld() );
   sqlite3_mutex_enter(pFile->pInode->pLockMutex);
 
   /* Check if a thread in this process holds such a lock */
   if( pFile->pInode->eFileLock>SHARED_LOCK ){
     reserved = 1;
@@ -1668,10 +1678,11 @@
   assert( eFileLock!=RESERVED_LOCK || pFile->eFileLock==SHARED_LOCK );
 
   /* This mutex is needed because pFile->pInode is shared across threads
   */
   pInode = pFile->pInode;
+  assert( unixMutexNotheld() );
   sqlite3_mutex_enter(pInode->pLockMutex);
 
   /* If some thread using this PID has a lock via a different unixFile*
   ** handle that precludes the requested lock, return BUSY.
   */
@@ -1860,10 +1871,11 @@
   assert( eFileLock<=SHARED_LOCK );
   if( pFile->eFileLock<=eFileLock ){
     return SQLITE_OK;
   }
   pInode = pFile->pInode;
+  assert( unixMutexNotheld() );
   sqlite3_mutex_enter(pInode->pLockMutex);
   assert( pInode->nShared!=0 );
   if( pFile->eFileLock>SHARED_LOCK ){
     assert( pInode->eFileLock==pFile->eFileLock );
 
@@ -2791,10 +2803,11 @@
   context = (afpLockingContext *) pFile->lockingContext;
   if( context->reserved ){
     *pResOut = 1;
     return SQLITE_OK;
   }
+  assert( unixMutexNotheld() );
   sqlite3_mutex_enter(pFile->pInode->pLockMutex);
   /* Check if a thread in this process holds such a lock */
   if( pFile->pInode->eFileLock>SHARED_LOCK ){
     reserved = 1;
   }
@@ -2879,10 +2892,11 @@
   assert( eFileLock!=RESERVED_LOCK || pFile->eFileLock==SHARED_LOCK );
   
   /* This mutex is needed because pFile->pInode is shared across threads
   */
   pInode = pFile->pInode;
+  assert( unixMutexNotheld() );
   sqlite3_mutex_enter(pInode->pLockMutex);
 
   /* If some thread using this PID has a lock via a different unixFile*
   ** handle that precludes the requested lock, return BUSY.
   */
@@ -3048,10 +3062,11 @@
   assert( eFileLock<=SHARED_LOCK );
   if( pFile->eFileLock<=eFileLock ){
     return SQLITE_OK;
   }
   pInode = pFile->pInode;
+  assert( unixMutexNotheld() );
   sqlite3_mutex_enter(pInode->pLockMutex);
   assert( pInode->nShared!=0 );
   if( pFile->eFileLock>SHARED_LOCK ){
     assert( pInode->eFileLock==pFile->eFileLock );
     SimulateIOErrorBenign(1);