Btrfs: fix btrfs_ordered_update_i_size to update disk_i_size properly

btrfs_ordered_update_i_size can be called by truncate and endio, but
only endio takes ordered_extent which contains the completed IO.

while truncating down a file, if there are some in-flight IOs,
btrfs_ordered_update_i_size in endio will set disk_i_size to
@orig_offset that is zero.  If truncating-down fails somehow, we try to
recover in memory isize with this zero'd disk_i_size.

Fix it by only updating disk_i_size with @orig_offset when
btrfs_ordered_update_i_size is not called from endio while truncating
down and waiting for in-flight IOs completing their work before recover
in-memory size.

Besides fixing the above issue, add an assertion for last_size to double
check we truncate down to the desired size.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -4695,6 +4695,13 @@ error:
 
 	btrfs_free_path(path);
 
+	if (err == 0) {
+		/* only inline file may have last_size != new_size */
+		if (new_size >= fs_info->sectorsize ||
+		    new_size > fs_info->max_inline)
+			ASSERT(last_size == new_size);
+	}
+
 	if (be_nice && bytes_deleted > SZ_32M) {
 		unsigned long updates = trans->delayed_ref_updates;
 		if (updates) {
@@ -5080,6 +5087,13 @@ static int btrfs_setsize(struct inode *inode, struct iattr *attr)
 		if (ret && inode->i_nlink) {
 			int err;
 
+			/* To get a stable disk_i_size */
+			err = btrfs_wait_ordered_range(inode, 0, (u64)-1);
+			if (err) {
+				btrfs_orphan_del(NULL, inode);
+				return err;
+			}
+
 			/*
 			 * failed to truncate, disk_i_size is only adjusted down
 			 * as we remove extents, so it should represent the true

fs/btrfs/ordered-data.c

@@ -984,8 +984,18 @@ int btrfs_ordered_update_i_size(struct inode *inode, u64 offset,
 	}
 	disk_i_size = BTRFS_I(inode)->disk_i_size;
 
-	/* truncate file */
-	if (disk_i_size > i_size) {
+	/*
+	 * truncate file.
+	 * If ordered is not NULL, then this is called from endio and
+	 * disk_i_size will be updated by either truncate itself or any
+	 * in-flight IOs which are inside the disk_i_size.
+	 *
+	 * Because btrfs_setsize() may set i_size with disk_i_size if truncate
+	 * fails somehow, we need to make sure we have a precise disk_i_size by
+	 * updating it as usual.
+	 *
+	 */
+	if (!ordered && disk_i_size > i_size) {
 		BTRFS_I(inode)->disk_i_size = orig_offset;
 		ret = 0;
 		goto out;