On Wed, Sep 30, 2015 at 12:11 PM, Zhao Lei <zhaolei@xxxxxxxxxxxxxx> wrote:
> Reproduce:
> (In integration-4.3 branch)
>
> TEST_DEV=(/dev/vdg /dev/vdh)
> TEST_DIR=/mnt/tmp
>
> umount "$TEST_DEV" >/dev/null
> mkfs.btrfs -f -d raid1 "${TEST_DEV[@]}"
>
> mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
> umount "$TEST_DEV"
>
> mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
> btrfs filesystem usage $TEST_DIR
>
> We can see the data chunk changed from raid1 to single:
> # btrfs filesystem usage $TEST_DIR
> Data,single: Size:8.00MiB, Used:0.00B
> /dev/vdg 8.00MiB
> #
>
> Reason:
> When a empty filesystem mount with -o nospace_cache, the last
> data blockgroup will be auto-removed in umount.
>
> Then if we mount it again, there is no data chunk in the
> filesystem, so the only available data profile is 0x0, result
> is all new chunks are created as single type.
>
> Fix:
> Don't auto-delete last blockgroup for a raid type.
>
> Test:
> Test by above script, and confirmed the logic by debug output.
>
> Changelog v1->v2:
> 1: Put code of checking block_group->list into
> semaphore of space_info->groups_sem.
> Noticed-by: Filipe Manana <fdmanana@xxxxxxxxx>
>
> Signed-off-by: Zhao Lei <zhaolei@xxxxxxxxxxxxxx>
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
I would have made the check in the "if" statement below that is
already done while holding a write lock on the semaphore (smaller code
diff), but this is equally correct.
thanks
> ---
> fs/btrfs/extent-tree.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 79a5bd9..ed9426c 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -10010,8 +10010,18 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
> block_group = list_first_entry(&fs_info->unused_bgs,
> struct btrfs_block_group_cache,
> bg_list);
> - space_info = block_group->space_info;
> list_del_init(&block_group->bg_list);
> +
> + space_info = block_group->space_info;
> +
> + down_read(&space_info->groups_sem);
> + if (block_group->list.next == block_group->list.prev) {
> + up_read(&space_info->groups_sem);
> + btrfs_put_block_group(block_group);
> + continue;
> + }
> + up_read(&space_info->groups_sem);
> +
> if (ret || btrfs_mixed_space_info(space_info)) {
> btrfs_put_block_group(block_group);
> continue;
> --
> 1.8.5.1
>
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--
Filipe David Manana,
"Reasonable men adapt themselves to the world.
Unreasonable men adapt the world to themselves.
That's why all progress depends on unreasonable men."
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