Re: [PATCH v2 1/2] btrfs: Fix lost-data-profile caused by auto removing bg

[Jeff Mahoney <jeffm@suse.com>]

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On 9/30/15 7:11 AM, Zhao Lei 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.

I still think this is kind of a hacky solution, but it's the best one
that doesn't involve a disk format change.

> 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@gmail.com>
> 
> Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com> --- 
> 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) {

		if (list_is_singular(&block_group->list)) {

> +			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;
> 

- -Jeff

- -- 
Jeff Mahoney
SUSE Labs
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