From 471c1fbbd23b21a2592eedadf583babc5d1288a5 Mon Sep 17 00:00:00 2001
From: Simon Rettberg
Date: Wed, 25 Oct 2017 16:46:06 +0200
Subject: [SERVER] Only start reloading images if no other reload is in
 progress

---
 LOCKS              |  2 +-
 src/server/image.c | 16 ++++++++++++----
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/LOCKS b/LOCKS
index a28e42a..7ba01ca 100644
--- a/LOCKS
+++ b/LOCKS
@@ -10,10 +10,10 @@ track of what's going on. ;)
 ===== SERVER =====
 This is a list of used locks, in the order they
 have to be aquired if you must hold multiple locks:
+remoteCloneLock | reloadLock
 _clients_lock
 _clients[].lock
 integrityQueueLock
-remoteCloneLock | reloadLock
 _images_lock
 _images[].lock
 pendingLockConsume
diff --git a/src/server/image.c b/src/server/image.c
index f277ed0..1905df1 100644
--- a/src/server/image.c
+++ b/src/server/image.c
@@ -570,9 +570,13 @@ bool image_loadAll(char *path)
 	dnbd3_image_t *imgHandle;
 
 	if ( path == NULL ) path = _basePath;
+	if ( pthread_mutex_trylock( &reloadLock ) != 0 ) {
+		logadd( LOG_MINOR, "Could not (re)load image list, already in progress." );
+		return false;
+	}
 	if ( _removeMissingImages ) {
 		// Check if all loaded images still exist on disk
-		logadd( LOG_DEBUG1, "Checking for vanished images" );
+		logadd( LOG_INFO, "Checking for vanished images" );
 		spin_lock( &imageListLock );
 		for ( int i = _num_images - 1; i >= 0; --i ) {
 			if ( _shutdown ) break;
@@ -595,6 +599,8 @@ bool image_loadAll(char *path)
 			spin_lock( &imgHandle->lock );
 			const bool freeImg = ( imgHandle->users == 0 );
 			spin_unlock( &imgHandle->lock );
+			// We unlocked, but the image has been removed from the list already, so
+			// there's no way the users-counter can increase at this point.
 			if ( freeImg ) {
 				// Image is not in use anymore, free the dangling entry immediately
 				spin_unlock( &imageListLock ); // image_free might do several fs operations; unlock
@@ -603,11 +609,13 @@ bool image_loadAll(char *path)
 			}
 		}
 		spin_unlock( &imageListLock );
-		if ( _shutdown ) return true;
+		if ( _shutdown ) {
+			pthread_mutex_unlock( &reloadLock );
+			return true;
+		}
 	}
 	// Now scan for new images
-	logadd( LOG_DEBUG1, "Scanning for new or modified images" );
-	pthread_mutex_lock( &reloadLock );
+	logadd( LOG_INFO, "Scanning for new or modified images" );
 	ret = image_load_all_internal( path, path );
 	pthread_mutex_unlock( &reloadLock );
 	logadd( LOG_INFO, "Finished scanning %s", path );
-- 
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