It turns out that pagerExclusiveLock() can be called with the lock state

already set to RESERVED if the SQLITE_FCNTL_PERSIST_WAL setting is set and
a specific sequence of multiple journal mode changes occur.
Enhance pagerExclusiveLock() to deal with this.
[forum:/forumpost/8130545bc6|Forum post 8130545bc6]

FossilOrigin-Name: 2bb8d977392f635515aa4a36f6f763a2e4858f7adc1120519e2e74c04a9749b5

1 files changed, 4 insertions, 2 deletions

diff --git a/src/pager.c b/src/pager.c
index 063b793f7..44384de5c 100644
--- a/src/pager.c
+++ b/src/pager.c
@@ -7473,13 +7473,15 @@ int sqlite3PagerWalSupported(Pager *pPager){
 */
 static int pagerExclusiveLock(Pager *pPager){
   int rc;                         /* Return code */
+  u8 eOrigLock;                   /* Original lock */
 
-  assert( pPager->eLock==SHARED_LOCK || pPager->eLock==EXCLUSIVE_LOCK );
+  assert( pPager->eLock>=SHARED_LOCK );
+  eOrigLock = pPager->eLock;
   rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
   if( rc!=SQLITE_OK ){
     /* If the attempt to grab the exclusive lock failed, release the 
     ** pending lock that may have been obtained instead.  */
-    pagerUnlockDb(pPager, SHARED_LOCK);
+    pagerUnlockDb(pPager, eOrigLock);
   }
 
   return rc;