Fix a problem causing the write-lock to be held when it should not be in some circumstances following a SEH exception.

FossilOrigin-Name: 7eb5accb7cf937fc967dcd86da0af813fb18a2697348bd231fbefd3c09b930ab

1 files changed, 14 insertions, 2 deletions

diff --git a/src/wal.c b/src/wal.c
index 5d6c0c62c..759ad8e10 100644
--- a/src/wal.c
+++ b/src/wal.c
@@ -502,6 +502,11 @@ struct WalCkptInfo {
 /*
 ** An open write-ahead log file is represented by an instance of the
 ** following object.
+**
+** writeLock:
+**   This is usually set to 1 whenever the WRITER lock is held. However,
+**   if it is set to 2, then the WRITER lock is held but must be released
+**   by walHandleException() if a SEH exception is thrown.
 */
 struct Wal {
   sqlite3_vfs *pVfs;         /* The VFS used to create pDbFd */
@@ -2413,7 +2418,9 @@ static int walHandleException(Wal *pWal){
     static const int S = 1;
     static const int E = (1<<SQLITE_SHM_NLOCK);
     int ii;
-    u32 mUnlock = pWal->lockMask & ~(
+    u32 mUnlock;
+    if( pWal->writeLock==2 ) pWal->writeLock = 0;
+    mUnlock = pWal->lockMask & ~(
         (pWal->readLock<0 ? 0 : (S << WAL_READ_LOCK(pWal->readLock)))
         | (pWal->writeLock ? (E << WAL_WRITE_LOCK) : 0)
         | (pWal->ckptLock ? (E << WAL_CKPT_LOCK) : 0)
@@ -2685,7 +2692,12 @@ static int walIndexReadHdr(Wal *pWal, int *pChanged){
       if( bWriteLock 
        || SQLITE_OK==(rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1)) 
       ){
-        pWal->writeLock = 1;
+        /* If the write-lock was just obtained, set writeLock to 2 instead of
+        ** the usual 1. This causes walIndexPage() to behave as if the 
+        ** write-lock were held (so that it allocates new pages as required),
+        ** and walHandleException() to unlock the write-lock if a SEH exception
+        ** is thrown.  */
+        if( !bWriteLock ) pWal->writeLock = 2;
         if( SQLITE_OK==(rc = walIndexPage(pWal, 0, &page0)) ){
           badHdr = walIndexTryHdr(pWal, pChanged);
           if( badHdr ){