ext4: warn on delalloc md block allocation without reservation

From: Brian Foster <[email protected]>

If we hit a condition where we have allocated metadata blocks that were not appropriately reserved, we risk underflow of ei->i_reserved_meta_blocks. In turn, this can throw sbi->s_dirtyclusters_counter significantly out of whack and undermine the nondelalloc fallback logic in ext4_nonda_switch(). Warn if this occurs and fix up the counter to handle only what we've reserved. This condition is reproduced by xfstests 270 against ext2 with delalloc enabled.

---
 fs/ext4/inode.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

index c77b0bd..b58845c 100644
@@ -279,6 +279,15 @@ void ext4_da_update_reserve_space(struct inode *inode,
 		used = ei->i_reserved_data_blocks;
 	}
 
+	if (unlikely(ei->i_allocated_meta_blocks > ei->i_reserved_meta_blocks)) {
+		ext4_msg(inode->i_sb, KERN_NOTICE, "%s: ino %lu, allocated %d "
+			 "with only %d reserved metadata blocks\n", __func__,
+			 inode->i_ino, ei->i_allocated_meta_blocks,
+			 ei->i_reserved_meta_blocks);
+		WARN_ON(1);
+		ei->i_allocated_meta_blocks = ei->i_reserved_meta_blocks;
+	}
+
 	/* Update per-inode reservations */
 	ei->i_reserved_data_blocks -= used;
 	ei->i_reserved_meta_blocks -= ei->i_allocated_meta_blocks;

1.7.7.6

Hi Brian,

Thanks for looking into this xfstests failure and proposing a bug fix. My apologies for not getting back to you until now.

I modified your commit description a little, but the patch looks good to me.

- Ted

Author: Brian Foster <[email protected]>
Date:   Sun Jul 22 23:59:40 2012 -0400

ext4: don't let i_reserved_meta_blocks go negative

If we hit a condition where we have allocated metadata blocks that were not appropriately reserved, we risk underflow of ei->i_reserved_meta_blocks. In turn, this can throw sbi->s_dirtyclusters_counter significantly out of whack and undermine the nondelalloc fallback logic in ext4_nonda_switch(). Warn if this occurs and set i_allocated_meta_blocks to avoid this problem.

This condition is reproduced by xfstests 270 against ext2 with delalloc enabled:

Mar 28 08:58:02 localhost kernel: [ 171.526344] EXT4-fs (loop1): delayed blo Mar 28 08:58:02 localhost kernel: [ 171.526346] EXT4-fs (loop1): This should

270 ultimately fails with an inconsistent filesystem and requires an fsck to repair. The cause of the error is an underflow in ext4_da_update_reserve_space() due to an unreserved meta block allocation.