[RFC PATCH 1/2] ext4: warn on delalloc md block allocation without reservation

[RFC PATCH 1/2] ext4: warn on delalloc md block allocation without reservation

[Brian Foster]

From: Brian Foster <bfoster@redhat.com>

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.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/ext4/inode.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c77b0bd..b58845c 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -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

Re: [RFC PATCH 1/2] ext4: warn on delalloc md block allocation without reservation

[Theodore Ts'o]

On Mon, Apr 02, 2012 at 11:14:13AM -0400, Brian Foster wrote:
> From: Brian Foster <bfoster@redhat.com>
> 
> 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.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>

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 <bfoster@redhat.com>
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.
    
    Signed-off-by: Brian Foster <bfoster@redhat.com>
    Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
    Cc: stable@vger.kernel.org