ext3: Avoid filesystem corruption after a crash under heavy delete load

It can happen that ext3_free_branches calls ext3_forget() for an indirect block
in an earlier transaction than a transaction in which we clear pointer to this
indirect block. Thus if we crash before a transaction clearing the block
pointer is committed, we will see indirect block pointing to already freed
blocks and complain during orphan list cleanup.

The fix is simple: Make sure ext3_forget() is called in the transaction
doing block pointer clearing.

This is a backport of an ext4 fix by Amir G. <amir73il@users.sourceforge.net>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/ext3/inode.c

@@ -2269,27 +2269,6 @@ static void ext3_free_branches(handle_t *handle, struct inode *inode,
 					   (__le32*)bh->b_data + addr_per_block,
 					   depth);
 
-			/*
-			 * We've probably journalled the indirect block several
-			 * times during the truncate.  But it's no longer
-			 * needed and we now drop it from the transaction via
-			 * journal_revoke().
-			 *
-			 * That's easy if it's exclusively part of this
-			 * transaction.  But if it's part of the committing
-			 * transaction then journal_forget() will simply
-			 * brelse() it.  That means that if the underlying
-			 * block is reallocated in ext3_get_block(),
-			 * unmap_underlying_metadata() will find this block
-			 * and will try to get rid of it.  damn, damn.
-			 *
-			 * If this block has already been committed to the
-			 * journal, a revoke record will be written.  And
-			 * revoke records must be emitted *before* clearing
-			 * this block's bit in the bitmaps.
-			 */
-			ext3_forget(handle, 1, inode, bh, bh->b_blocknr);
-
 			/*
 			 * Everything below this this pointer has been
 			 * released.  Now let this top-of-subtree go.
@@ -2313,6 +2292,31 @@ static void ext3_free_branches(handle_t *handle, struct inode *inode,
 				truncate_restart_transaction(handle, inode);
 			}
 
+			/*
+			 * We've probably journalled the indirect block several
+			 * times during the truncate.  But it's no longer
+			 * needed and we now drop it from the transaction via
+			 * journal_revoke().
+			 *
+			 * That's easy if it's exclusively part of this
+			 * transaction.  But if it's part of the committing
+			 * transaction then journal_forget() will simply
+			 * brelse() it.  That means that if the underlying
+			 * block is reallocated in ext3_get_block(),
+			 * unmap_underlying_metadata() will find this block
+			 * and will try to get rid of it.  damn, damn. Thus
+			 * we don't allow a block to be reallocated until
+			 * a transaction freeing it has fully committed.
+			 *
+			 * We also have to make sure journal replay after a
+			 * crash does not overwrite non-journaled data blocks
+			 * with old metadata when the block got reallocated for
+			 * data.  Thus we have to store a revoke record for a
+			 * block in the same transaction in which we free the
+			 * block.
+			 */
+			ext3_forget(handle, 1, inode, bh, bh->b_blocknr);
+
 			ext3_free_blocks(handle, inode, nr, 1);
 
 			if (parent_bh) {