Implemented bdi_inc_writeback() to increase the writeback context
count and called this function at XFS mount time to set the desired
count.

Signed-off-by: Kundan Kumar <kundan.kumar@samsung.com>
Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
---
 fs/xfs/xfs_super.c          |  2 ++
 include/linux/backing-dev.h |  1 +
 mm/backing-dev.c            | 58 +++++++++++++++++++++++++++++++++++++
 3 files changed, 61 insertions(+)

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index b3ec9141d902..aa97b59f53c6 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1783,6 +1783,8 @@ xfs_fs_fill_super(
 	if (error)
 		goto out_free_sb;
 
+	bdi_inc_writeback(sb->s_bdi, mp->m_sb.sb_agcount);
+
 	/*
 	 * V4 support is undergoing deprecation.
 	 *
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 14f53183b8d1..89a465e1964f 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -40,6 +40,7 @@ void wb_start_background_writeback(struct bdi_writeback *wb);
 void wb_workfn(struct work_struct *work);
 
 void wb_wait_for_completion(struct wb_completion *done);
+int bdi_inc_writeback(struct backing_dev_info *bdi, int nwriteback);
 
 extern spinlock_t bdi_lock;
 extern struct list_head bdi_list;
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 5bfb9bf3ce52..e450b3a9b952 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -1219,6 +1219,64 @@ struct backing_dev_info *bdi_alloc(int node_id)
 }
 EXPORT_SYMBOL(bdi_alloc);
 
+int bdi_inc_writeback(struct backing_dev_info *bdi, int nwritebacks)
+{
+	struct bdi_writeback_ctx **wb_ctx;
+	int ret = 0;
+
+	if (nwritebacks <= bdi->nr_wb_ctx)
+		return ret;
+
+	wb_ctx = kcalloc(nwritebacks, sizeof(struct bdi_writeback_ctx *),
+			 GFP_KERNEL);
+	if (!wb_ctx)
+		return -ENOMEM;
+
+	for (int i = 0; i < bdi->nr_wb_ctx; i++)
+		wb_ctx[i] = bdi->wb_ctx[i];
+
+	for (int i = bdi->nr_wb_ctx; i < nwritebacks; i++) {
+		wb_ctx[i] = (struct bdi_writeback_ctx *)
+			kzalloc(sizeof(struct bdi_writeback_ctx), GFP_KERNEL);
+		if (!wb_ctx[i]) {
+			pr_err("Failed to allocate %d", i);
+			while (--i >= bdi->nr_wb_ctx)
+				kfree(wb_ctx[i]);
+			kfree(wb_ctx);
+			return -ENOMEM;
+		}
+		INIT_LIST_HEAD(&wb_ctx[i]->wb_list);
+		init_waitqueue_head(&wb_ctx[i]->wb_waitq);
+
+#ifdef CONFIG_CGROUP_WRITEBACK
+		INIT_RADIX_TREE(&wb_ctx[i]->cgwb_tree, GFP_ATOMIC);
+		init_rwsem(&wb_ctx[i]->wb_switch_rwsem);
+#endif
+		ret = wb_init(&wb_ctx[i]->wb, wb_ctx[i], bdi, GFP_KERNEL);
+		if (!ret) {
+#ifdef CONFIG_CGROUP_WRITEBACK
+			wb_ctx[i]->wb.memcg_css = &root_mem_cgroup->css;
+			wb_ctx[i]->wb.blkcg_css = blkcg_root_css;
+#endif
+		} else {
+			while (--i >= bdi->nr_wb_ctx)
+				kfree(wb_ctx[i]);
+			kfree(wb_ctx);
+			return ret;
+		}
+		cgwb_bdi_register(bdi, wb_ctx[i]);
+		set_bit(WB_registered, &wb_ctx[i]->wb.state);
+	}
+
+	spin_lock_bh(&bdi_lock);
+	kfree(bdi->wb_ctx);
+	bdi->wb_ctx = wb_ctx;
+	bdi->nr_wb_ctx = nwritebacks;
+	spin_unlock_bh(&bdi_lock);
+	return 0;
+}
+EXPORT_SYMBOL(bdi_inc_writeback);
+
 static struct rb_node **bdi_lookup_rb_node(u64 id, struct rb_node **parentp)
 {
 	struct rb_node **p = &bdi_tree.rb_node;
-- 
2.25.1