Deal with page == NULL in the btrfs_unplug_io_fn

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 30 insertions, 2 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 7f5aca35494d..19c258d2c7e2 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -911,12 +911,40 @@ static int btrfs_congested_fn(void *congested_data, int bdi_bits)
         return ret;
 }
 
+/*
+ * this unplugs every device on the box, and it is only used when page
+ * is null
+ */
+static void __unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
+{
+        struct list_head *cur;
+        struct btrfs_device *device;
+        struct btrfs_fs_info *info;
+
+        info = (struct btrfs_fs_info *)bdi->unplug_io_data;
+        list_for_each(cur, &info->fs_devices->devices) {
+                device = list_entry(cur, struct btrfs_device, dev_list);
+                bdi = blk_get_backing_dev_info(device->bdev);
+                if (bdi->unplug_io_fn) {
+                        bdi->unplug_io_fn(bdi, page);
+                }
+        }
+}
+
 void btrfs_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
 {
-        struct inode *inode = page->mapping->host;
+        struct inode *inode;
         struct extent_map_tree *em_tree;
         struct extent_map *em;
-        u64 offset = page_offset(page);
+        u64 offset;
+
+        if (!page) {
+                __unplug_io_fn(bdi, page);
+                return;
+        }
+
+        inode = page->mapping->host;
+        offset = page_offset(page);
 
         em_tree = &BTRFS_I(inode)->extent_tree;
         spin_lock(&em_tree->lock);