On Mon, Oct 16, 2017 at 12:22:44PM +0800, Anand Jain wrote:
>
>
> On 10/14/2017 04:51 AM, Liu Bo wrote:
> >On Wed, Oct 11, 2017 at 10:38:50AM +0300, Nikolay Borisov wrote:
> >>
> >>
> >>On 10.10.2017 20:53, Liu Bo wrote:
> >>>We've avoided data losing raid profile when doing balance, but it
> >>>turns out that deleting a device could also result in the same
> >>>problem
> >>>
> >>>This fixes the problem by creating an empty data chunk before
> >>>relocating the data chunk.
> >>
> >>Why is this needed - copy the metadata of the to-be-relocated chunk into
> >>the newly created empty chunk? I don't entirely understand that code but
> >>doesn't this seem a bit like a hack in order to stash some information?
> >>Perhaps you could elaborate the logic a bit more in the changelog?
> >>
> >>>
> >>>Metadata/System chunk are supposed to have non-zero bytes all the time
> >>>so their raid profile is persistent.
> >>
> >>I think this changelog is a bit scarce on detail as to the culprit of
> >>the problem. Could you perhaps put a sentence or two what the underlying
> >>logic which deletes the raid profile if a chunk is empty ?
> >>
> >
> >Fair enough.
> >
> >The problem is as same as what commit 2c9fe8355258 ("btrfs: Fix
> >lost-data-profile caused by balance bg") had fixed.
> >
> >Similar to doing balance, deleting a device can also move all chunks
> >on this disk to other available disks, after 'move' successfully,
> >it'll remove those chunks.
> >
> >If our last data chunk is empty and part of it happens to be on this
> >disk, then there is no data chunk in this btrfs after deleting the
> >device successfully, any following write will try to create a new data
> >chunk which ends up with a single data chunk because the only
> >available data raid profile is 'single'.
>
> So you are referring to a raid1 group profile which contains 3 or more
> devices otherwise single group file is what it will fit ? Is there
> reproducer ?
[PATCH] Fstest: btrfs/151: test if device delete ends up with losing raid
profile
Thanks,
-liubo
>
> Thanks, Anand
>
>
> >thanks,
> >-liubo
> >
> >>>
> >>>Reported-by: James Alandt <james.ala...@wdc.com>
> >>>Signed-off-by: Liu Bo <bo.li....@oracle.com>
> >>>---
> >>>
> >>>v2: - return the correct error.
> >>> - move helper ahead of __btrfs_balance().
> >>>
> >>> fs/btrfs/volumes.c | 84
> >>> ++++++++++++++++++++++++++++++++++++++++++------------
> >>> 1 file changed, 65 insertions(+), 19 deletions(-)
> >>>
> >>>diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> >>>index 4a72c45..a74396d 100644
> >>>--- a/fs/btrfs/volumes.c
> >>>+++ b/fs/btrfs/volumes.c
> >>>@@ -3018,6 +3018,48 @@ static int btrfs_relocate_sys_chunks(struct
> >>>btrfs_fs_info *fs_info)
> >>> return ret;
> >>> }
> >>>+/*
> >>>+ * return 1 : allocate a data chunk successfully,
> >>>+ * return <0: errors during allocating a data chunk,
> >>>+ * return 0 : no need to allocate a data chunk.
> >>>+ */
> >>>+static int btrfs_may_alloc_data_chunk(struct btrfs_fs_info *fs_info,
> >>>+ u64 chunk_offset)
> >>>+{
> >>>+ struct btrfs_block_group_cache *cache;
> >>>+ u64 bytes_used;
> >>>+ u64 chunk_type;
> >>>+
> >>>+ cache = btrfs_lookup_block_group(fs_info, chunk_offset);
> >>>+ ASSERT(cache);
> >>>+ chunk_type = cache->flags;
> >>>+ btrfs_put_block_group(cache);
> >>>+
> >>>+ if (chunk_type & BTRFS_BLOCK_GROUP_DATA) {
> >>>+ spin_lock(&fs_info->data_sinfo->lock);
> >>>+ bytes_used = fs_info->data_sinfo->bytes_used;
> >>>+ spin_unlock(&fs_info->data_sinfo->lock);
> >>>+
> >>>+ if (!bytes_used) {
> >>>+ struct btrfs_trans_handle *trans;
> >>>+ int ret;
> >>>+
> >>>+ trans = btrfs_join_transaction(fs_info->tree_root);
> >>>+ if (IS_ERR(trans))
> >>>+ return PTR_ERR(trans);
> >>>+
> >>>+ ret = btrfs_force_chunk_alloc(trans, fs_info,
> >>>+ BTRFS_BLOCK_GROUP_DATA);
> >>>+ btrfs_end_transaction(trans);
> >>>+ if (ret < 0)
> >>>+ return ret;
> >>>+
> >>>+ return 1;
> >>>+ }
> >>>+ }
> >>>+ return 0;
> >>>+}
> >>>+
> >>> static int insert_balance_item(struct btrfs_fs_info *fs_info,
> >>> struct btrfs_balance_control *bctl)
> >>> {
> >>>@@ -3476,7 +3518,6 @@ static int __btrfs_balance(struct btrfs_fs_info
> >>>*fs_info)
> >>> u32 count_meta = 0;
> >>> u32 count_sys = 0;
> >>> int chunk_reserved = 0;
> >>>- u64 bytes_used = 0;
> >>> /* step one make some room on all the devices */
> >>> devices = &fs_info->fs_devices->devices;
> >>>@@ -3635,28 +3676,21 @@ static int __btrfs_balance(struct btrfs_fs_info
> >>>*fs_info)
> >>> goto loop;
> >>> }
> >>>- ASSERT(fs_info->data_sinfo);
> >>>- spin_lock(&fs_info->data_sinfo->lock);
> >>>- bytes_used = fs_info->data_sinfo->bytes_used;
> >>>- spin_unlock(&fs_info->data_sinfo->lock);
> >>>-
> >>>- if ((chunk_type & BTRFS_BLOCK_GROUP_DATA) &&
> >>>- !chunk_reserved && !bytes_used) {
> >>>- trans = btrfs_start_transaction(chunk_root, 0);
> >>>- if (IS_ERR(trans)) {
> >>>- mutex_unlock(&fs_info->delete_unused_bgs_mutex);
> >>>- ret = PTR_ERR(trans);
> >>>- goto error;
> >>>- }
> >>>-
> >>>- ret = btrfs_force_chunk_alloc(trans, fs_info,
> >>>- BTRFS_BLOCK_GROUP_DATA);
> >>>- btrfs_end_transaction(trans);
> >>>+ if (!chunk_reserved) {
> >>>+ /*
> >>>+ * We may be relocating the only data chunk we have,
> >>>+ * which could potentially end up with losing data's
> >>>+ * raid profile, so lets allocate an empty one in
> >>>+ * advance.
> >>>+ */
> >>>+ ret = btrfs_may_alloc_data_chunk(fs_info,
> >>>+ found_key.offset);
> >>> if (ret < 0) {
> >>> mutex_unlock(&fs_info->delete_unused_bgs_mutex);
> >>> goto error;
> >>>+ } else if (ret == 1) {
> >>>+ chunk_reserved = 1;
> >>> }
> >>>- chunk_reserved = 1;
> >>> }
> >>> ret = btrfs_relocate_chunk(fs_info, found_key.offset);
> >>>@@ -4419,6 +4453,18 @@ int btrfs_shrink_device(struct btrfs_device
> >>>*device, u64 new_size)
> >>> chunk_offset = btrfs_dev_extent_chunk_offset(l, dev_extent);
> >>> btrfs_release_path(path);
> >>>+ /*
> >>>+ * We may be relocating the only data chunk we have,
> >>>+ * which could potentially end up with losing data's
> >>>+ * raid profile, so lets allocate an empty one in
> >>>+ * advance.
> >>>+ */
> >>>+ ret = btrfs_may_alloc_data_chunk(fs_info, chunk_offset);
> >>>+ if (ret < 0) {
> >>>+ mutex_unlock(&fs_info->delete_unused_bgs_mutex);
> >>>+ goto done;
> >>>+ }
> >>>+
> >>> ret = btrfs_relocate_chunk(fs_info, chunk_offset);
> >>> mutex_unlock(&fs_info->delete_unused_bgs_mutex);
> >>> if (ret && ret != -ENOSPC)
> >>>
> >--
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