fellow_log: rewrite the log for a clean shutdown

src/fellow_log.c

@@ -6110,11 +6110,13 @@ fellow_logwatcher_thread(void *priv)
 	while (ffd->watcher_running) {
 		fellow_fd_update_space_stats(ffd);
 
-		if (new_log_fdr.size)
+		if (new_log_fdr.size || ffd->watcher_running == 2)
 			need = FLW_NEED_REWRITE;
 		else
 			need = fellow_logwatcher_need(ffd, NULL);
 
+		ffd->watcher_running = 1;
+
 		switch (need) {
 		case FLW_NEED_NONE:
 			DBG("logwatcher %s", "FLW_NEED_NONE");
@@ -6140,10 +6142,7 @@ fellow_logwatcher_thread(void *priv)
 			fellow_logwatcher_flush(ffd, 0);
 			ffd->watcher_state = FLW_S_REWRITING;
 			AZ(pthread_mutex_unlock(&ffd->logmtx));
-			if (new_log_fdr.size ||
-			    fellow_logwatcher_need(ffd, NULL) == need)
-				fellow_logs_rewrite(ffd, &new_log_fdr,
-				    NULL, NULL);
+			fellow_logs_rewrite(ffd, &new_log_fdr, NULL, NULL);
 			AZ(pthread_mutex_lock(&ffd->logmtx));
 			continue;
 		default:
@@ -6221,10 +6220,20 @@ fellow_logwatcher_fini(struct fellow_fd *ffd)
 {
 	CHECK_OBJ_NOTNULL(ffd, FELLOW_FD_MAGIC);
 
+	AZ(pthread_mutex_lock(&ffd->logmtx));
+	ffd->watcher_running = 2;
+	AZ(pthread_cond_signal(&ffd->watcher_cond));
+	AZ(pthread_mutex_unlock(&ffd->logmtx));
+
+	while (ffd->watcher_running == 2)
+		(void) usleep (100*1000);
+	assert(ffd->watcher_running == 1);
+
 	AZ(pthread_mutex_lock(&ffd->logmtx));
 	ffd->watcher_running = 0;
 	AZ(pthread_cond_signal(&ffd->watcher_cond));
 	AZ(pthread_mutex_unlock(&ffd->logmtx));
+
 	AZ(pthread_join(ffd->watcher_thread, NULL));
 	AZ(pthread_cond_destroy(&ffd->watcher_cond));
 }

src/vmod_slash.man.rst

@@ -488,7 +488,10 @@ Resizing fellow storage
 In general, resizing a fellow storage is supported by restarting
 varnishd with different parameters (be it on the command line or in
 VCL), but for size reductions, cache contents may be lost, to the
-extent of all cache contents. Read this paragraph for details:
+extent of all cache contents. Read this paragraph for details.
+
+Before applying any size change, it is strongly recommended to cleanly
+shut down fellow using ``varnishadm stop``.
 
 Increasing ``memsize``
 

src/vmod_slash.vcc

@@ -432,7 +432,10 @@ Resizing fellow storage
 In general, resizing a fellow storage is supported by restarting
 varnishd with different parameters (be it on the command line or in
 VCL), but for size reductions, cache contents may be lost, to the
-extent of all cache contents. Read this paragraph for details:
+extent of all cache contents. Read this paragraph for details.
+
+Before applying any size change, it is strongly recommended to cleanly
+shut down fellow using ``varnishadm stop``.
 
 Increasing ``memsize``