Btrfs: Add more synchronization before creating a snapshot

File data checksums are only done during writepage, so we have to make sure
all pages are written when the snapshot is taken.  This also adds some
locking so that new writes don't race in and add new dirty pages.

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

1 files changed, 9 insertions, 1 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 6b3e4404dc6a..1ace6d11e097 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -686,6 +686,7 @@ static int btrfs_truncate_page(struct address_space *mapping, loff_t from)
         if ((offset & (blocksize - 1)) == 0)
                 goto out;
 
+        down_read(&BTRFS_I(inode)->root->snap_sem);
         ret = -ENOMEM;
         page = grab_cache_page(mapping, index);
         if (!page)
@@ -704,6 +705,7 @@ static int btrfs_truncate_page(struct address_space *mapping, loff_t from)
 
         unlock_page(page);
         page_cache_release(page);
+        up_read(&BTRFS_I(inode)->root->snap_sem);
 out:
         return ret;
 }
@@ -1668,6 +1670,7 @@ int btrfs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
         int ret = -EINVAL;
         u64 page_start;
 
+        down_read(&BTRFS_I(inode)->root->snap_sem);
         lock_page(page);
         wait_on_page_writeback(page);
         size = i_size_read(inode);
@@ -1688,6 +1691,7 @@ int btrfs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
         ret = btrfs_cow_one_page(inode, page, end);
 
 out_unlock:
+        up_read(&BTRFS_I(inode)->root->snap_sem);
         unlock_page(page);
         return ret;
 }
@@ -1851,6 +1855,10 @@ static int create_snapshot(struct btrfs_root *root, char *name, int namelen)
         if (!root->ref_cows)
                 return -EINVAL;
 
+        down_write(&root->snap_sem);
+        freeze_bdev(root->fs_info->sb->s_bdev);
+        thaw_bdev(root->fs_info->sb->s_bdev, root->fs_info->sb);
+
         mutex_lock(&root->fs_info->fs_mutex);
         trans = btrfs_start_transaction(root, 1);
         BUG_ON(!trans);
@@ -1894,12 +1902,12 @@ static int create_snapshot(struct btrfs_root *root, char *name, int namelen)
         ret = btrfs_inc_root_ref(trans, root);
         if (ret)
                 goto fail;
-
 fail:
         err = btrfs_commit_transaction(trans, root);
         if (err && !ret)
                 ret = err;
         mutex_unlock(&root->fs_info->fs_mutex);
+        up_write(&root->snap_sem);
         btrfs_btree_balance_dirty(root);
         return ret;
 }