drbd: Removed a race that could cause unexpected execution of w_make_resync_request()

The actual race happened int the drbd_start_resync() function. Where
drbd_resync_finished() -> __drbd_set_state() set STOP_SYNC_TIMER and
armed the timer.

If the timer fired before execution reaches the mod_timer statement
at the end of drbd_start_resync() the latter would cause an
unexpected call to w_make_resync_request().

Removed the STOP_SYNC_TIMER bit, and base it on the connection state.

The STOP_SYNC_TIMER bit probably originates probably the time before
the state engine.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_int.h

@@ -827,7 +827,6 @@ enum {
 	SIGNAL_ASENDER,		/* whether asender wants to be interrupted */
 	SEND_PING,		/* whether asender should send a ping asap */
 
-	STOP_SYNC_TIMER,	/* tell timer to cancel itself */
 	UNPLUG_QUEUED,		/* only relevant with kernel 2.4 */
 	UNPLUG_REMOTE,		/* sending a "UnplugRemote" could help */
 	MD_DIRTY,		/* current uuids and flags not yet on disk */

drivers/block/drbd/drbd_main.c

@@ -1052,12 +1052,6 @@ int __drbd_set_state(struct drbd_conf *mdev,
 	wake_up(&mdev->misc_wait);
 	wake_up(&mdev->state_wait);
 
-	/*   post-state-change actions   */
-	if (os.conn >= C_SYNC_SOURCE   && ns.conn <= C_CONNECTED) {
-		set_bit(STOP_SYNC_TIMER, &mdev->flags);
-		mod_timer(&mdev->resync_timer, jiffies);
-	}
-
 	/* aborted verify run. log the last position */
 	if ((os.conn == C_VERIFY_S || os.conn == C_VERIFY_T) &&
 	    ns.conn < C_CONNECTED) {
@@ -1072,22 +1066,14 @@ int __drbd_set_state(struct drbd_conf *mdev,
 		dev_info(DEV, "Syncer continues.\n");
 		mdev->rs_paused += (long)jiffies
 				  -(long)mdev->rs_mark_time[mdev->rs_last_mark];
-		if (ns.conn == C_SYNC_TARGET) {
-			if (!test_and_clear_bit(STOP_SYNC_TIMER, &mdev->flags))
-				mod_timer(&mdev->resync_timer, jiffies);
-			/* This if (!test_bit) is only needed for the case
-			   that a device that has ceased to used its timer,
-			   i.e. it is already in drbd_resync_finished() gets
-			   paused and resumed. */
-		}
+		if (ns.conn == C_SYNC_TARGET)
+			mod_timer(&mdev->resync_timer, jiffies);
 	}
 
 	if ((os.conn == C_SYNC_TARGET  || os.conn == C_SYNC_SOURCE) &&
 	    (ns.conn == C_PAUSED_SYNC_T || ns.conn == C_PAUSED_SYNC_S)) {
 		dev_info(DEV, "Resync suspended\n");
 		mdev->rs_mark_time[mdev->rs_last_mark] = jiffies;
-		if (ns.conn == C_PAUSED_SYNC_T)
-			set_bit(STOP_SYNC_TIMER, &mdev->flags);
 	}
 
 	if (os.conn == C_CONNECTED &&

drivers/block/drbd/drbd_receiver.c

@@ -3803,7 +3803,6 @@ static void drbd_disconnect(struct drbd_conf *mdev)
 
 	/* make sure syncer is stopped and w_resume_next_sg queued */
 	del_timer_sync(&mdev->resync_timer);
-	set_bit(STOP_SYNC_TIMER, &mdev->flags);
 	resync_timer_fn((unsigned long)mdev);
 
 	/* wait for all w_e_end_data_req, w_e_end_rsdata_req, w_send_barrier,

drivers/block/drbd/drbd_worker.c

@@ -395,25 +395,22 @@ static int read_for_csum(struct drbd_conf *mdev, sector_t sector, int size)
 
 void resync_timer_fn(unsigned long data)
 {
-	unsigned long flags;
 	struct drbd_conf *mdev = (struct drbd_conf *) data;
 	int queue;
 
-	spin_lock_irqsave(&mdev->req_lock, flags);
-
-	if (likely(!test_and_clear_bit(STOP_SYNC_TIMER, &mdev->flags))) {
-		queue = 1;
-		if (mdev->state.conn == C_VERIFY_S)
-			mdev->resync_work.cb = w_make_ov_request;
-		else
-			mdev->resync_work.cb = w_make_resync_request;
-	} else {
+	queue = 1;
+	switch (mdev->state.conn) {
+	case C_VERIFY_S:
+		mdev->resync_work.cb = w_make_ov_request;
+		break;
+	case C_SYNC_TARGET:
+		mdev->resync_work.cb = w_make_resync_request;
+		break;
+	default:
 		queue = 0;
 		mdev->resync_work.cb = w_resync_inactive;
 	}
 
-	spin_unlock_irqrestore(&mdev->req_lock, flags);
-
 	/* harmless race: list_empty outside data.work.q_lock */
 	if (list_empty(&mdev->resync_work.list) && queue)
 		drbd_queue_work(&mdev->data.work, &mdev->resync_work);