On Tue, Oct 02, 2012 at 12:53:47AM +0200, Willy Tarreau wrote:
> 2.6.32-longterm review patch. If anyone has any objections, please let me
> know.
>
> ------------------
>
> From: Brian Foster <bfos...@redhat.com>
>
> commit 97795d2a5b8d3c8dc4365d4bd3404191840453ba upstream.
>
> 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
> block allocation failed for inode 14 at logical offset 64486 with max blocks
> 64 with error -28
> Mar 28 08:58:02 localhost kernel: [ 171.526346] EXT4-fs (loop1): This should
> not happen!! Data will be lost
>
> 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.
[...]
> + 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;
> + }
[...]
This seems to be working around a bug elsewhere. Has the underlying
bug been fixed in mainline yet?
Ben.
--
Ben Hutchings
We get into the habit of living before acquiring the habit of thinking.
- Albert Camus
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