MDEV-28689, MDEV-28690: Incorrect error handling for ctrl_mutex

comp_thread_ctxt_t: Remove ctrl_mutex, ctrl_cond, started. We do not
actually need them for anything.

destroy_worker_thread(): Split from destroy_worker_threads().

create_worker_threads(): We already initialize
thd->data_avail=FALSE and thd->cancelled=FALSE before
invoking pthread_create(). If any thread creation fails,
clean up by destroy_worker_thread().

compress_worker_thread_func(): Assume that thd->started and
thd->data_avail are already initialized.

Reviewed by: Vladislav Vaintroub

extra/mariabackup/ds_compress.cc

@@ -1,5 +1,6 @@
 /******************************************************
 Copyright (c) 2011-2013 Percona LLC and/or its affiliates.
+Copyright (c) 2022, MariaDB Corporation.
 
 Compressing datasink implementation for XtraBackup.
 
@@ -32,11 +33,8 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1335  USA
 typedef struct {
 	pthread_t		id;
 	uint			num;
-	pthread_mutex_t 	ctrl_mutex;
-	pthread_cond_t		ctrl_cond;
 	pthread_mutex_t		data_mutex;
 	pthread_cond_t  	data_cond;
-	my_bool			started;
 	my_bool			data_avail;
 	my_bool			cancelled;
 	const char 		*from;
@@ -208,14 +206,13 @@ compress_write(ds_file_t *file, const uchar *buf, size_t len)
 
 			thd = threads + i;
 
-			pthread_mutex_lock(&thd->ctrl_mutex);
+			pthread_mutex_lock(&thd->data_mutex);
 
 			chunk_len = (len > COMPRESS_CHUNK_SIZE) ?
 				COMPRESS_CHUNK_SIZE : len;
 			thd->from = ptr;
 			thd->from_len = chunk_len;
 
-			pthread_mutex_lock(&thd->data_mutex);
 			thd->data_avail = TRUE;
 			pthread_cond_signal(&thd->data_cond);
 			pthread_mutex_unlock(&thd->data_mutex);
@@ -260,7 +257,6 @@ compress_write(ds_file_t *file, const uchar *buf, size_t len)
 			}
 
 			pthread_mutex_unlock(&threads[i].data_mutex);
-			pthread_mutex_unlock(&threads[i].ctrl_mutex);
 		}
 	}
 
@@ -330,6 +326,23 @@ write_uint64_le(ds_file_t *file, ulonglong n)
 	return ds_write(file, tmp, sizeof(tmp));
 }
 
+static
+void
+destroy_worker_thread(comp_thread_ctxt_t *thd)
+{
+	pthread_mutex_lock(&thd->data_mutex);
+	thd->cancelled = TRUE;
+	pthread_cond_signal(&thd->data_cond);
+	pthread_mutex_unlock(&thd->data_mutex);
+
+	pthread_join(thd->id, NULL);
+
+	pthread_cond_destroy(&thd->data_cond);
+	pthread_mutex_destroy(&thd->data_mutex);
+
+	my_free(thd->to);
+}
+
 static
 comp_thread_ctxt_t *
 create_worker_threads(uint n)
@@ -344,54 +357,32 @@ create_worker_threads(uint n)
 		comp_thread_ctxt_t *thd = threads + i;
 
 		thd->num = i + 1;
-		thd->started = FALSE;
 		thd->cancelled = FALSE;
 		thd->data_avail = FALSE;
 
 		thd->to = (char *) my_malloc(COMPRESS_CHUNK_SIZE +
 						   MY_QLZ_COMPRESS_OVERHEAD,
 						   MYF(MY_FAE));
 
-		/* Initialize the control mutex and condition var */
-		if (pthread_mutex_init(&thd->ctrl_mutex, NULL) ||
-		    pthread_cond_init(&thd->ctrl_cond, NULL)) {
-			goto err;
-		}
-
 		/* Initialize and data mutex and condition var */
 		if (pthread_mutex_init(&thd->data_mutex, NULL) ||
 		    pthread_cond_init(&thd->data_cond, NULL)) {
 			goto err;
 		}
 
-		pthread_mutex_lock(&thd->ctrl_mutex);
-
 		if (pthread_create(&thd->id, NULL, compress_worker_thread_func,
 				   thd)) {
 			msg("compress: pthread_create() failed: "
 			    "errno = %d", errno);
-			pthread_mutex_unlock(&thd->ctrl_mutex);
 			goto err;
 		}
 	}
 
-	/* Wait for the threads to start */
-	for (i = 0; i < n; i++) {
-		comp_thread_ctxt_t *thd = threads + i;
-
-		while (thd->started == FALSE)
-			pthread_cond_wait(&thd->ctrl_cond, &thd->ctrl_mutex);
-		pthread_mutex_unlock(&thd->ctrl_mutex);
-	}
-
 	return threads;
 
 err:
-	while (i > 0) {
-		comp_thread_ctxt_t *thd;
-		i--;
-		thd = threads + i;
-		pthread_mutex_unlock(&thd->ctrl_mutex);
+	for (; i; i--) {
+		destroy_worker_thread(threads + i);
 	}
 
 	my_free(threads);
@@ -405,21 +396,7 @@ destroy_worker_threads(comp_thread_ctxt_t *threads, uint n)
 	uint i;
 
 	for (i = 0; i < n; i++) {
-		comp_thread_ctxt_t *thd = threads + i;
-
-		pthread_mutex_lock(&thd->data_mutex);
-		threads[i].cancelled = TRUE;
-		pthread_cond_signal(&thd->data_cond);
-		pthread_mutex_unlock(&thd->data_mutex);
-
-		pthread_join(thd->id, NULL);
-
-		pthread_cond_destroy(&thd->data_cond);
-		pthread_mutex_destroy(&thd->data_mutex);
-		pthread_cond_destroy(&thd->ctrl_cond);
-		pthread_mutex_destroy(&thd->ctrl_mutex);
-
-		my_free(thd->to);
+		destroy_worker_thread(threads + i);
 	}
 
 	my_free(threads);
@@ -431,19 +408,9 @@ compress_worker_thread_func(void *arg)
 {
 	comp_thread_ctxt_t *thd = (comp_thread_ctxt_t *) arg;
 
-	pthread_mutex_lock(&thd->ctrl_mutex);
-
 	pthread_mutex_lock(&thd->data_mutex);
 
-	thd->started = TRUE;
-	pthread_cond_signal(&thd->ctrl_cond);
-
-	pthread_mutex_unlock(&thd->ctrl_mutex);
-
 	while (1) {
-		thd->data_avail = FALSE;
-		pthread_cond_signal(&thd->data_cond);
-
 		while (!thd->data_avail && !thd->cancelled) {
 			pthread_cond_wait(&thd->data_cond, &thd->data_mutex);
 		}