gfs2: Get rid of some unnecessary quota locking

With the locking the previous patch has introduced for each struct
gfs2_quota_data object, sd_quota_mutex has become largely irrelevant.
By waiting on the buffer head instead of waiting on the mutex in
get_bh(), it becomes completely irrelevant and can be removed.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/incore.h

@@ -782,7 +782,6 @@ struct gfs2_sbd {
 
 	struct list_head sd_quota_list;
 	atomic_t sd_quota_count;
-	struct mutex sd_quota_mutex;
 	struct mutex sd_quota_sync_mutex;
 	wait_queue_head_t sd_quota_wait;
 

fs/gfs2/ops_fstype.c

@@ -103,7 +103,6 @@ static struct gfs2_sbd *init_sbd(struct super_block *sb)
 	init_completion(&sdp->sd_journal_ready);
 
 	INIT_LIST_HEAD(&sdp->sd_quota_list);
-	mutex_init(&sdp->sd_quota_mutex);
 	mutex_init(&sdp->sd_quota_sync_mutex);
 	init_waitqueue_head(&sdp->sd_quota_wait);
 	spin_lock_init(&sdp->sd_bitmap_lock);

fs/gfs2/quota.c

@@ -397,16 +397,17 @@ static int bh_get(struct gfs2_quota_data *qd)
 	struct inode *inode = sdp->sd_qc_inode;
 	struct gfs2_inode *ip = GFS2_I(inode);
 	unsigned int block, offset;
-	struct buffer_head *bh;
+	struct buffer_head *bh = NULL;
 	struct iomap iomap = { };
 	int error;
 
-	mutex_lock(&sdp->sd_quota_mutex);
-
-	if (qd->qd_bh_count++) {
-		mutex_unlock(&sdp->sd_quota_mutex);
+	spin_lock(&qd->qd_lockref.lock);
+	if (qd->qd_bh_count) {
+		qd->qd_bh_count++;
+		spin_unlock(&qd->qd_lockref.lock);
 		return 0;
 	}
+	spin_unlock(&qd->qd_lockref.lock);
 
 	block = qd->qd_slot / sdp->sd_qc_per_block;
 	offset = qd->qd_slot % sdp->sd_qc_per_block;
@@ -415,48 +416,50 @@ static int bh_get(struct gfs2_quota_data *qd)
 			       (loff_t)block << inode->i_blkbits,
 			       i_blocksize(inode), &iomap);
 	if (error)
-		goto fail;
+		return error;
 	error = -ENOENT;
 	if (iomap.type != IOMAP_MAPPED)
-		goto fail;
+		return error;
 
 	error = gfs2_meta_read(ip->i_gl, iomap.addr >> inode->i_blkbits,
 			       DIO_WAIT, 0, &bh);
 	if (error)
-		goto fail;
+		return error;
 	error = -EIO;
 	if (gfs2_metatype_check(sdp, bh, GFS2_METATYPE_QC))
-		goto fail_brelse;
-
-	qd->qd_bh = bh;
-	qd->qd_bh_qc = (struct gfs2_quota_change *)
-		(bh->b_data + sizeof(struct gfs2_meta_header) +
-		 offset * sizeof(struct gfs2_quota_change));
-
-	mutex_unlock(&sdp->sd_quota_mutex);
+		goto out;
 
-	return 0;
+	spin_lock(&qd->qd_lockref.lock);
+	if (qd->qd_bh == NULL) {
+		qd->qd_bh = bh;
+		qd->qd_bh_qc = (struct gfs2_quota_change *)
+			(bh->b_data + sizeof(struct gfs2_meta_header) +
+			 offset * sizeof(struct gfs2_quota_change));
+		bh = NULL;
+	}
+	qd->qd_bh_count++;
+	spin_unlock(&qd->qd_lockref.lock);
+	error = 0;
 
-fail_brelse:
+out:
 	brelse(bh);
-fail:
-	qd->qd_bh_count--;
-	mutex_unlock(&sdp->sd_quota_mutex);
 	return error;
 }
 
 static void bh_put(struct gfs2_quota_data *qd)
 {
 	struct gfs2_sbd *sdp = qd->qd_sbd;
+	struct buffer_head *bh = NULL;
 
-	mutex_lock(&sdp->sd_quota_mutex);
+	spin_lock(&qd->qd_lockref.lock);
 	gfs2_assert(sdp, qd->qd_bh_count);
 	if (!--qd->qd_bh_count) {
-		brelse(qd->qd_bh);
+		bh = qd->qd_bh;
 		qd->qd_bh = NULL;
 		qd->qd_bh_qc = NULL;
 	}
-	mutex_unlock(&sdp->sd_quota_mutex);
+	spin_unlock(&qd->qd_lockref.lock);
+	brelse(bh);
 }
 
 static bool qd_grab_sync(struct gfs2_sbd *sdp, struct gfs2_quota_data *qd,
@@ -676,7 +679,6 @@ static void do_qc(struct gfs2_quota_data *qd, s64 change)
 	bool needs_put = false;
 	s64 x;
 
-	mutex_lock(&sdp->sd_quota_mutex);
 	gfs2_trans_add_meta(ip->i_gl, qd->qd_bh);
 
 	/*
@@ -720,7 +722,6 @@ static void do_qc(struct gfs2_quota_data *qd, s64 change)
 	}
 	if (change < 0) /* Reset quiet flag if we freed some blocks */
 		clear_bit(QDF_QMSG_QUIET, &qd->qd_flags);
-	mutex_unlock(&sdp->sd_quota_mutex);
 }
 
 static int gfs2_write_buf_to_page(struct gfs2_sbd *sdp, unsigned long index,