Excerpts from liubo's message of 2011-02-24 07:48:22 -0500:
> On 02/24/2011 04:13 PM, Daniel J Blueman wrote:
> > When creating a filesystem (single or redundant) with BTRFS and
> > subsequently executing a balance [1], we see a kernel oops at the next
> > mount [2].
> >
>
> Hi, Daniel,
>
> After digging this, I've come up with a patch on this, would you please test
> it on your box? Hopes that this is helpful, Thanks.
>
> From: Liu Bo <liubo2009@xxxxxxxxxxxxxx>
>
> [PATCH] btrfs: fix OOPS of empty filesystem after balance
>
> btrfs will exclude unused block groups via a thread.
> When a empty filesystem is balanced, the block group with tag "DATA" may be dropped,
> and after umount, this will lead to OOPS when we mount it again.
Thanks for tracking this down! Comment below:
>
> Signed-off-by: Liu Bo <liubo2009@xxxxxxxxxxxxxx>
> ---
> fs/btrfs/extent-tree.c | 16 ++++++++++++++--
> 1 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 100e409..4749ab0 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -3856,10 +3856,14 @@ static void update_global_block_rsv(struct btrfs_fs_info *fs_info)
> spin_unlock(&block_rsv->lock);
> }
>
> -static void init_global_block_rsv(struct btrfs_fs_info *fs_info)
> +static int init_global_block_rsv(struct btrfs_fs_info *fs_info)
> {
> struct btrfs_space_info *space_info;
>
> + space_info = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_DATA);
> + if (!space_info)
> + return -EAGAIN;
> +
> space_info = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_SYSTEM);
> fs_info->chunk_block_rsv.space_info = space_info;
> fs_info->chunk_block_rsv.priority = 10;
> @@ -3884,6 +3888,8 @@ static void init_global_block_rsv(struct btrfs_fs_info *fs_info)
> btrfs_add_durable_block_rsv(fs_info, &fs_info->delalloc_block_rsv);
>
> update_global_block_rsv(fs_info);
> +
> + return 0;
> }
>
> static void release_global_block_rsv(struct btrfs_fs_info *fs_info)
> @@ -8514,7 +8520,13 @@ int btrfs_read_block_groups(struct btrfs_root *root)
> set_block_group_ro(cache);
> }
>
> - init_global_block_rsv(info);
> +again:
> + ret = init_global_block_rsv(info);
> + if (ret == -EAGAIN) {
> + update_space_info(info, BTRFS_BLOCK_GROUP_DATA, 0, 0,
> + &space_info);
> + goto again;
> + }
> ret = 0;
Are we looping here because we expect the init_global_block_rsv to fail
more than once? If so we need a cond_resched or something in there.
But if the EAGAIN is only returned once we should avoid the loop and
open code the call again.
-chris
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