Index: src/pager.c
==================================================================
--- src/pager.c
+++ src/pager.c
@@ -399,12 +399,12 @@
   int nHash;                  /* Size of the pager hash table */
   PgHdr **aHash;              /* Hash table to map page number to PgHdr */
 #ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
   Pager *pNext;               /* Doubly linked list of pagers on which */
   Pager *pPrev;               /* sqlite3_release_memory() will work */
-  int iInUseMM;               /* Non-zero if unavailable to MM */
-  int iInUseDB;               /* Non-zero if in sqlite3_release_memory() */
+  volatile int iInUseMM;      /* Non-zero if unavailable to MM */
+  volatile int iInUseDB;      /* Non-zero if in sqlite3_release_memory() */
   u8 onPagerList;             /* True if part of the sqlite3PagerList */
 #endif
   char *pTmpSpace;            /* Pager.pageSize bytes of space for tmp use */
   char dbFileVers[16];        /* Changes whenever database file changes */
 };
@@ -525,14 +525,14 @@
       sqlite3_mutex *mutex;
       mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MEM2);
 #endif
       p->iInUseDB = 0;
       sqlite3_mutex_enter(mutex);
+      assert( p->iInUseMM==0 );
       p->iInUseDB = 1;
       sqlite3_mutex_leave(mutex);
     }
-    assert( p->iInUseMM==0 );
   }
   static void pagerLeave(Pager *p){
     p->iInUseDB--;
     assert( p->iInUseDB>=0 );
   }
@@ -704,10 +704,11 @@
     return;
   }
   sqlite3_free(pPager->aHash);
   pPager->nHash = N;
   pPager->aHash = aHash;
+  pagerMutexHeld(pPager);
   for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
     int h;
     if( pPg->pgno==0 ){
       assert( pPg->pNextHash==0 && pPg->pPrevHash==0 );
       continue;
@@ -1422,10 +1423,11 @@
         rc = sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
       }
     }
     sqlite3BitvecDestroy(pPager->pInJournal);
     pPager->pInJournal = 0;
+    pagerMutexHeld(pPager);
     for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
       pPg->inJournal = 0;
       pPg->dirty = 0;
       pPg->needSync = 0;
       pPg->alwaysRollback = 0;
@@ -2939,10 +2941,11 @@
   /* If the Pager.needSync flag is clear then the PgHdr.needSync
   ** flag must also be clear for all pages.  Verify that this
   ** invariant is true.
   */
   else{
+    pagerMutexHeld(pPager);
     for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
       assert( pPg->needSync==0 );
     }
     assert( pPager->lru.pFirstSynced==pPager->lru.pFirst );
   }
@@ -3177,11 +3180,11 @@
   PgHdr *pPg;
   *ppPg = 0;
 
   /* It is illegal to call this function unless the pager object
   ** pointed to by pPager has at least one free page (page with nRef==0).
-  */ 
+  */
   assert(!MEMDB);
   assert(pPager->lru.pFirst);
 
   /* Find a page to recycle.  Try to locate a page that does not
   ** require us to do an fsync() on the journal.
@@ -3626,13 +3629,16 @@
 */
 static int pagerAllocatePage(Pager *pPager, PgHdr **ppPg){
   int rc = SQLITE_OK;
   PgHdr *pPg;
   int nByteHdr;
+
 
   /* Create a new PgHdr if any of the four conditions defined 
-  ** above are met: */
+  ** above are met: 
+  */
+  pagerMutexHeld(pPager);
   if( pPager->nPage<pPager->mxPage
    || pPager->lru.pFirst==0 
    || MEMDB
    || (pPager->lru.pFirstSynced==0 && pPager->doNotSync)
   ){
@@ -3662,15 +3668,17 @@
       goto pager_allocate_out;
     }
     memset(pPg, 0, nByteHdr);
     pPg->pData = pData;
     pPg->pPager = pPager;
+    pagerMutexHeld(pPager);
     pPg->pNextAll = pPager->pAll;
     pPager->pAll = pPg;
     pPager->nPage++;
   }else{
     /* Recycle an existing page with a zero ref-count. */
+    pagerMutexHeld(pPager);
     rc = pager_recycle(pPager, &pPg);
     if( rc==SQLITE_BUSY ){
       rc = SQLITE_IOERR_BLOCKED;
     }
     if( rc!=SQLITE_OK ){
@@ -4713,10 +4721,11 @@
         } 
       }
 #endif
       rc = writeMasterJournal(pPager, zMaster);
       if( rc!=SQLITE_OK ) goto sync_exit;
+      pagerMutexHeld(pPager);
       rc = syncJournal(pPager);
     }
     if( rc!=SQLITE_OK ) goto sync_exit;
 
 #ifndef SQLITE_OMIT_AUTOVACUUM
@@ -4840,10 +4849,11 @@
 int sqlite3PagerRollback(Pager *pPager){
   int rc;
   PAGERTRACE2("ROLLBACK %d\n", PAGERID(pPager));
   if( MEMDB ){
     PgHdr *p;
+    pagerMutexHeld(pPager);
     for(p=pPager->pAll; p; p=p->pNextAll){
       PgHistory *pHist;
       assert( !p->alwaysRollback );
       if( !p->dirty ){
         assert( !((PgHistory *)PGHDR_TO_HIST(p, pPager))->pOrig );