On Mon, Jul 14, 2008 at 09:28:17AM -0700, Mingming Cao wrote:
>
> Ext4: Fix delalloc enospace handling counter update race
>
> From: Mingming Cao <cmm@xxxxxxxxxx>
>
> Ext4 delalloc reserve meta blocks ahead of time so later when real block
> allocation fs will not short of free blocks for allocating meta blocks.
> It keeps track of the real number of new allocated meta data blocks, so
> after block allocation it will update how much meta data blocks still
> need to be reserved for that inode.
>
> Both per inode reserved metadata blocks and per-allocation allocated metablocks
> are protected by the per inode delalloc reservation lock. The per-allocation
> allocated metablocks counter should be protected by the i_data_sem as well,
> so that it could avoid race with other block allocation to the same inode
> in parallel. The patch moves the code under the i_data_sem protection.
>
> Also in the case of truncate, we should not clear the per-allocation allocated
> metablocks counter as that may be in-use by parallel allocation. The patch
> only clear the per-allocation allocated metablocks when allocation is successfully returned.
>
>
> Signed-off-by: Mingming Cao <cmm@xxxxxxxxxx>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
>
> ---
> fs/ext4/inode.c | 19 +++++++++++++------
> 1 file changed, 13 insertions(+), 6 deletions(-)
>
> Index: linux-2.6.26-rc9/fs/ext4/inode.c
> ===================================================================
> --- linux-2.6.26-rc9.orig/fs/ext4/inode.c 2008-07-14 08:54:25.000000000 -0700
> +++ linux-2.6.26-rc9/fs/ext4/inode.c 2008-07-14 09:23:29.000000000 -0700
> @@ -1060,8 +1060,18 @@ int ext4_get_blocks_wrap(handle_t *handl
> ~EXT4_EXT_MIGRATE;
> }
> }
> - if (flag)
> +
> + if (flag) {
> EXT4_I(inode)->i_delalloc_reserved_flag = 0;
> + /*
> + * Update reserved blocks/metadata blocks
> + * after successful block allocation
> + * which were deferred till now
> + */
> + if ((retval > 0) && buffer_delay(bh))
> + ext4_da_release_space(inode, retval, 0);
> + }
> +
> up_write((&EXT4_I(inode)->i_data_sem));
> return retval;
> }
> @@ -1519,7 +1529,8 @@ void ext4_da_release_space(struct inode
>
> BUG_ON(mdb > EXT4_I(inode)->i_reserved_meta_blocks);
> EXT4_I(inode)->i_reserved_meta_blocks = mdb;
> - EXT4_I(inode)->i_allocated_meta_blocks = 0;
> + if (used)
> + EXT4_I(inode)->i_allocated_meta_blocks = 0;
> spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
> }
>
> @@ -2005,10 +2016,6 @@ static int ext4_da_get_block_write(struc
> if (ret > 0) {
> bh_result->b_size = (ret << inode->i_blkbits);
>
> - /* release reserved-but-unused meta blocks */
> - if (buffer_delay(bh_result))
> - ext4_da_release_space(inode, ret, 0);
> -
> /*
> * Update on-disk size along with block allocation
> * we don't use 'extend_disksize' as size may change
>
>
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