ext4: fix error handling in ext4_ext_truncate()

Previously ext4_ext_truncate() was ignoring potential error returns
from ext4_es_remove_extent() and ext4_ext_remove_space().  This can
lead to the on-diks extent tree and the extent status tree cache
getting out of sync, which is particuarlly bad, and can lead to file
system corruption and potential data loss.
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org

fs/ext4/extents.c

@@ -4405,9 +4405,20 @@ void ext4_ext_truncate(handle_t *handle, struct inode *inode)
 
 	last_block = (inode->i_size + sb->s_blocksize - 1)
 			>> EXT4_BLOCK_SIZE_BITS(sb);
+retry:
 	err = ext4_es_remove_extent(inode, last_block,
 				    EXT_MAX_BLOCKS - last_block);
+	if (err == ENOMEM) {
+		cond_resched();
+		congestion_wait(BLK_RW_ASYNC, HZ/50);
+		goto retry;
+	}
+	if (err) {
+		ext4_std_error(inode->i_sb, err);
+		return;
+	}
 	err = ext4_ext_remove_space(inode, last_block, EXT_MAX_BLOCKS - 1);
+	ext4_std_error(inode->i_sb, err);
 }
 
 static void ext4_falloc_update_inode(struct inode *inode,