dm thin: send event about thin-pool state change _after_ making it

Sending a DM event before a thin-pool state change is about to happen is
a bug.  It wasn't realized until it became clear that userspace response
to the event raced with the actual state change that the event was
meant to notify about.

Fix this by first updating internal thin-pool state to reflect what the
DM event is being issued about.  This fixes a long-standing racey/buggy
userspace device-mapper-test-suite 'resize_io' test that would get an
event but not find the state it was looking for -- so it would just go
on to hang because no other events caused the test to reevaluate the
thin-pool's state.

Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-thin.c

@@ -195,7 +195,7 @@ static void throttle_unlock(struct throttle *t)
 struct dm_thin_new_mapping;
 
 /*
- * The pool runs in 4 modes.  Ordered in degraded order for comparisons.
+ * The pool runs in various modes.  Ordered in degraded order for comparisons.
  */
 enum pool_mode {
 	PM_WRITE,		/* metadata may be changed */
@@ -282,9 +282,38 @@ struct pool {
 	mempool_t mapping_pool;
 };
 
-static enum pool_mode get_pool_mode(struct pool *pool);
 static void metadata_operation_failed(struct pool *pool, const char *op, int r);
 
+static enum pool_mode get_pool_mode(struct pool *pool)
+{
+	return pool->pf.mode;
+}
+
+static void notify_of_pool_mode_change(struct pool *pool)
+{
+	const char *descs[] = {
+		"write",
+		"out-of-data-space",
+		"read-only",
+		"read-only",
+		"fail"
+	};
+	const char *extra_desc = NULL;
+	enum pool_mode mode = get_pool_mode(pool);
+
+	if (mode == PM_OUT_OF_DATA_SPACE) {
+		if (!pool->pf.error_if_no_space)
+			extra_desc = " (queue IO)";
+		else
+			extra_desc = " (error IO)";
+	}
+
+	dm_table_event(pool->ti->table);
+	DMINFO("%s: switching pool to %s%s mode",
+	       dm_device_name(pool->pool_md),
+	       descs[(int)mode], extra_desc ? : "");
+}
+
 /*
  * Target context for a pool.
  */
@@ -2351,8 +2380,6 @@ static void do_waker(struct work_struct *ws)
 	queue_delayed_work(pool->wq, &pool->waker, COMMIT_PERIOD);
 }
 
-static void notify_of_pool_mode_change_to_oods(struct pool *pool);
-
 /*
  * We're holding onto IO to allow userland time to react.  After the
  * timeout either the pool will have been resized (and thus back in
@@ -2365,7 +2392,7 @@ static void do_no_space_timeout(struct work_struct *ws)
 
 	if (get_pool_mode(pool) == PM_OUT_OF_DATA_SPACE && !pool->pf.error_if_no_space) {
 		pool->pf.error_if_no_space = true;
-		notify_of_pool_mode_change_to_oods(pool);
+		notify_of_pool_mode_change(pool);
 		error_retry_list_with_code(pool, BLK_STS_NOSPC);
 	}
 }
@@ -2433,26 +2460,6 @@ static void noflush_work(struct thin_c *tc, void (*fn)(struct work_struct *))
 
 /*----------------------------------------------------------------*/
 
-static enum pool_mode get_pool_mode(struct pool *pool)
-{
-	return pool->pf.mode;
-}
-
-static void notify_of_pool_mode_change(struct pool *pool, const char *new_mode)
-{
-	dm_table_event(pool->ti->table);
-	DMINFO("%s: switching pool to %s mode",
-	       dm_device_name(pool->pool_md), new_mode);
-}
-
-static void notify_of_pool_mode_change_to_oods(struct pool *pool)
-{
-	if (!pool->pf.error_if_no_space)
-		notify_of_pool_mode_change(pool, "out-of-data-space (queue IO)");
-	else
-		notify_of_pool_mode_change(pool, "out-of-data-space (error IO)");
-}
-
 static bool passdown_enabled(struct pool_c *pt)
 {
 	return pt->adjusted_pf.discard_passdown;
@@ -2501,8 +2508,6 @@ static void set_pool_mode(struct pool *pool, enum pool_mode new_mode)
 
 	switch (new_mode) {
 	case PM_FAIL:
-		if (old_mode != new_mode)
-			notify_of_pool_mode_change(pool, "failure");
 		dm_pool_metadata_read_only(pool->pmd);
 		pool->process_bio = process_bio_fail;
 		pool->process_discard = process_bio_fail;
@@ -2516,8 +2521,6 @@ static void set_pool_mode(struct pool *pool, enum pool_mode new_mode)
 
 	case PM_OUT_OF_METADATA_SPACE:
 	case PM_READ_ONLY:
-		if (!is_read_only_pool_mode(old_mode))
-			notify_of_pool_mode_change(pool, "read-only");
 		dm_pool_metadata_read_only(pool->pmd);
 		pool->process_bio = process_bio_read_only;
 		pool->process_discard = process_bio_success;
@@ -2538,8 +2541,6 @@ static void set_pool_mode(struct pool *pool, enum pool_mode new_mode)
 		 * alarming rate.  Adjust your low water mark if you're
 		 * frequently seeing this mode.
 		 */
-		if (old_mode != new_mode)
-			notify_of_pool_mode_change_to_oods(pool);
 		pool->out_of_data_space = true;
 		pool->process_bio = process_bio_read_only;
 		pool->process_discard = process_discard_bio;
@@ -2552,8 +2553,6 @@ static void set_pool_mode(struct pool *pool, enum pool_mode new_mode)
 		break;
 
 	case PM_WRITE:
-		if (old_mode != new_mode)
-			notify_of_pool_mode_change(pool, "write");
 		if (old_mode == PM_OUT_OF_DATA_SPACE)
 			cancel_delayed_work_sync(&pool->no_space_timeout);
 		pool->out_of_data_space = false;
@@ -2573,6 +2572,9 @@ static void set_pool_mode(struct pool *pool, enum pool_mode new_mode)
 	 * doesn't cause an unexpected mode transition on resume.
 	 */
 	pt->adjusted_pf.mode = new_mode;
+
+	if (old_mode != new_mode)
+		notify_of_pool_mode_change(pool);
 }
 
 static void abort_transaction(struct pool *pool)