GFS2: Use reflink for quota data cache

This patch adds reflink support to the quota data cache. It
looks a bit strange because we still don't have a sensible
split in the lookup by id and the lru list. That is coming in
later patches though.

The intent here is just to swap the current ref count for
reflinks in all cases with as little as possible other change.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Abhijith Das <adas@redhat.com>
Tested-by: Abhijith Das <adas@redhat.com>

fs/gfs2/incore.h

@@ -422,7 +422,7 @@ struct gfs2_quota_data {
 	struct list_head qd_list;
 	struct list_head qd_reclaim;
 
-	atomic_t qd_count;
+	struct lockref qd_lockref;
 
 	struct kqid qd_id;
 	unsigned long qd_flags;		/* QDF_... */

fs/gfs2/quota.c

@@ -50,6 +50,7 @@
 #include <linux/freezer.h>
 #include <linux/quota.h>
 #include <linux/dqblk_xfs.h>
+#include <linux/lockref.h>
 
 #include "gfs2.h"
 #include "incore.h"
@@ -148,7 +149,8 @@ static int qd_alloc(struct gfs2_sbd *sdp, struct kqid qid,
 	if (!qd)
 		return -ENOMEM;
 
-	atomic_set(&qd->qd_count, 1);
+	qd->qd_lockref.count = 1;
+	spin_lock_init(&qd->qd_lockref.lock);
 	qd->qd_id = qid;
 	qd->qd_slot = -1;
 	INIT_LIST_HEAD(&qd->qd_reclaim);
@@ -180,13 +182,12 @@ static int qd_get(struct gfs2_sbd *sdp, struct kqid qid,
 		spin_lock(&qd_lru_lock);
 		list_for_each_entry(qd, &sdp->sd_quota_list, qd_list) {
 			if (qid_eq(qd->qd_id, qid)) {
-				if (!atomic_read(&qd->qd_count) &&
-				    !list_empty(&qd->qd_reclaim)) {
+				lockref_get(&qd->qd_lockref);
+				if (!list_empty(&qd->qd_reclaim)) {
 					/* Remove it from reclaim list */
 					list_del_init(&qd->qd_reclaim);
 					atomic_dec(&qd_lru_count);
 				}
-				atomic_inc(&qd->qd_count);
 				found = 1;
 				break;
 			}
@@ -222,18 +223,24 @@ static int qd_get(struct gfs2_sbd *sdp, struct kqid qid,
 static void qd_hold(struct gfs2_quota_data *qd)
 {
 	struct gfs2_sbd *sdp = qd->qd_gl->gl_sbd;
-	gfs2_assert(sdp, atomic_read(&qd->qd_count));
-	atomic_inc(&qd->qd_count);
+	gfs2_assert(sdp, !__lockref_is_dead(&qd->qd_lockref));
+	lockref_get(&qd->qd_lockref);
 }
 
 static void qd_put(struct gfs2_quota_data *qd)
 {
-	if (atomic_dec_and_lock(&qd->qd_count, &qd_lru_lock)) {
+	spin_lock(&qd_lru_lock);
+
+	if (!lockref_put_or_lock(&qd->qd_lockref)) {
+
 		/* Add to the reclaim list */
 		list_add_tail(&qd->qd_reclaim, &qd_lru_list);
 		atomic_inc(&qd_lru_count);
-		spin_unlock(&qd_lru_lock);
+
+		spin_unlock(&qd->qd_lockref.lock);
 	}
+
+	spin_unlock(&qd_lru_lock);
 }
 
 static int slot_get(struct gfs2_quota_data *qd)
@@ -394,8 +401,8 @@ static int qd_check_sync(struct gfs2_sbd *sdp, struct gfs2_quota_data *qd,
 	list_move_tail(&qd->qd_list, &sdp->sd_quota_list);
 
 	set_bit(QDF_LOCKED, &qd->qd_flags);
-	gfs2_assert_warn(sdp, atomic_read(&qd->qd_count));
-	atomic_inc(&qd->qd_count);
+	gfs2_assert_warn(sdp, !__lockref_is_dead(&qd->qd_lockref));
+	lockref_get(&qd->qd_lockref);
 	qd->qd_change_sync = qd->qd_change;
 	gfs2_assert_warn(sdp, qd->qd_slot_count);
 	qd->qd_slot_count++;
@@ -1303,15 +1310,22 @@ void gfs2_quota_cleanup(struct gfs2_sbd *sdp)
 	while (!list_empty(head)) {
 		qd = list_entry(head->prev, struct gfs2_quota_data, qd_list);
 
-		if (atomic_read(&qd->qd_count) > 1 ||
-		    (atomic_read(&qd->qd_count) &&
-		     !test_bit(QDF_CHANGE, &qd->qd_flags))) {
+		/*
+		 * To be removed in due course... we should be able to
+		 * ensure that all refs to the qd have done by this point
+		 * so that this rather odd test is not required
+		 */
+		spin_lock(&qd->qd_lockref.lock);
+		if (qd->qd_lockref.count > 1 ||
+		    (qd->qd_lockref.count && !test_bit(QDF_CHANGE, &qd->qd_flags))) {
+			spin_unlock(&qd->qd_lockref.lock);
 			list_move(&qd->qd_list, head);
 			spin_unlock(&qd_lru_lock);
 			schedule();
 			spin_lock(&qd_lru_lock);
 			continue;
 		}
+		spin_unlock(&qd->qd_lockref.lock);
 
 		list_del(&qd->qd_list);
 		/* Also remove if this qd exists in the reclaim list */
@@ -1322,7 +1336,7 @@ void gfs2_quota_cleanup(struct gfs2_sbd *sdp)
 		atomic_dec(&sdp->sd_quota_count);
 		spin_unlock(&qd_lru_lock);
 
-		if (!atomic_read(&qd->qd_count)) {
+		if (!qd->qd_lockref.count) {
 			gfs2_assert_warn(sdp, !qd->qd_change);
 			gfs2_assert_warn(sdp, !qd->qd_slot_count);
 		} else