Re: [PATCH 1/3] btrfs-progs: check/lowmem: Check and repair root generation

[Nikolay Borisov <nborisov@suse.com>]

On 10.08.19 г. 3:30 ч., Qu Wenruo wrote:
> 
> 
> On 2019/8/10 上午12:10, Nikolay Borisov wrote:
>>
>>
>> On 9.08.19 г. 9:53 ч., Qu Wenruo wrote:
>>> Since kernel is going to reject any root item which is newer than super
>>> block generation, we need to provide a way to fix such problem in
>>> btrfs-check.
>>>
>>> This patch addes the ability to report and repair root generation in
>>> lowmem mode.
>>>
>>> This is done by cowing the root node, so we will update the root
>>> generation along with the root node generation at commit transaction
>>> time.
>>>
>>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>>> ---
>>>  check/mode-common.c | 29 +++++++++++++++++++++++++++++
>>>  check/mode-common.h |  1 +
>>>  check/mode-lowmem.c | 16 ++++++++++++++++
>>>  check/mode-lowmem.h |  1 +
>>>  4 files changed, 47 insertions(+)
>>>
>>> diff --git a/check/mode-common.c b/check/mode-common.c
>>> index d5f6c8ef97b1..a5b86a0ac32a 100644
>>> --- a/check/mode-common.c
>>> +++ b/check/mode-common.c
>>> @@ -924,3 +924,32 @@ int check_repair_free_space_inode(struct btrfs_fs_info *fs_info,
>>>  	}
>>>  	return ret;
>>>  }
>>> +
>>> +int repair_root_generation(struct btrfs_root *root)
>>> +{
>>> +	struct btrfs_trans_handle *trans;
>>> +	struct btrfs_path path;
>>> +	struct btrfs_key key;
>>> +	int ret;
>>> +
>>> +	trans = btrfs_start_transaction(root, 1);
>>> +	if (IS_ERR(trans))
>>> +		return PTR_ERR(trans);
>>> +
>>> +	key.objectid = 0;
>>> +	key.type = 0;
>>> +	key.offset = 0;
>>> +	btrfs_init_path(&path);
>>> +
>>> +	/* Here we only CoW the tree root to update the geneartion */
>>> +	path.lowest_level = btrfs_header_level(root->node);
>>> +	root->node->flags |= EXTENT_BAD_TRANSID;
>>
>> Why do you set EXTENT_BAD_TRANSID? This flag is currently used only in
>> read_tree_block to link blocks which have failed ordinary validation to
>> the recow_ebs list, and this only happens in case we have a single copy
>> for this eb. This list is then processed in the main check logic.
> 
> Because we have extra transid check in
> btrfs_search_slot()/btrfs_cow_block().
> 
> EXTENT_BAD_TRANSID is to suppress such warning.

nod

> 
>>
>> So repair_root_generation could possibly be as simple as just linking
>> root->node to the fs_info->recow_ebs and leave the rest to the existing
>> logic?
> 
> It doesn't change the root generation.

recow_extent_buffer seems to be doing exactly the same thing
repair_root_generation does - findw the root item and commits the
transaction. What am I missing?

> 
>>
>>> +
>>> +	ret = btrfs_search_slot(trans, root, &key, &path, 0, 1);
>>> +	if (ret < 0)
>>> +		return ret;
>>> +
>>> +	btrfs_release_path(&path);
>>> +	ret = btrfs_commit_transaction(trans, root);
>>> +	return ret;
>>> +}
>>> diff --git a/check/mode-common.h b/check/mode-common.h
>>> index 4c169c6e3b29..4a3abeb02c81 100644
>>> --- a/check/mode-common.h
>>> +++ b/check/mode-common.h
>>> @@ -155,4 +155,5 @@ static inline bool is_valid_imode(u32 imode)
>>>  	return true;
>>>  }
>>>
>>> +int repair_root_generation(struct btrfs_root *root);
>>>  #endif
>>> diff --git a/check/mode-lowmem.c b/check/mode-lowmem.c
>>> index a2be0e6d7034..bf3b57f5ad2d 100644
>>> --- a/check/mode-lowmem.c
>>> +++ b/check/mode-lowmem.c
>>> @@ -4957,6 +4957,7 @@ static int check_btrfs_root(struct btrfs_root *root, int check_all)
>>>  	struct btrfs_path path;
>>>  	struct node_refs nrefs;
>>>  	struct btrfs_root_item *root_item = &root->root_item;
>>> +	u64 super_generation = btrfs_super_generation(root->fs_info->super_copy);
>>>  	int ret;
>>>  	int level;
>>>  	int err = 0;
>>> @@ -4978,6 +4979,21 @@ static int check_btrfs_root(struct btrfs_root *root, int check_all)
>>>  	level = btrfs_header_level(root->node);
>>>  	btrfs_init_path(&path);
>>>
>>> +	if (btrfs_root_generation(root_item) > super_generation + 1) {
>>> +		error(
>>> +	"invalid root generation for root %llu, have %llu expect (0, %llu)",
>>> +		      root->root_key.objectid, btrfs_root_generation(root_item),
>>> +		      super_generation + 1);
>>> +		err |= INVALID_GENERATION;
>>> +		if (repair) {
>>> +			ret = repair_root_generation(root);
>>> +			if (!ret) {
>>> +				err &= ~INVALID_GENERATION;
>>> +				printf("Reset generation for root %llu\n",
>>> +					root->root_key.objectid);
>>> +			}
>>> +		}
>>> +	}
>>>  	if (btrfs_root_refs(root_item) > 0 ||
>>>  	    btrfs_disk_key_objectid(&root_item->drop_progress) == 0) {
>>>  		path.nodes[level] = root->node;
>>> diff --git a/check/mode-lowmem.h b/check/mode-lowmem.h
>>> index d2983fd12eb4..0361fb3382b1 100644
>>> --- a/check/mode-lowmem.h
>>> +++ b/check/mode-lowmem.h
>>> @@ -47,6 +47,7 @@
>>>  #define INODE_FLAGS_ERROR	(1<<23) /* Invalid inode flags */
>>>  #define DIR_ITEM_HASH_MISMATCH	(1<<24) /* Dir item hash mismatch */
>>>  #define INODE_MODE_ERROR	(1<<25) /* Bad inode mode */
>>> +#define INVALID_GENERATION	(1<<26)	/* Generation is too new */
>>>
>>>  /*
>>>   * Error bit for low memory mode check.
>>>
>