Re: [patch 9/9] btrfs: Push up non-looped btrfs_start_transaction failures

[Jeff Mahoney <jeffm@suse.com>]

On 08/10/2011 09:27 PM, Tsutomu Itoh wrote:
> Hi, Jeff,
> 
> (2011/08/11 8:20), Jeff Mahoney wrote:
>>   This patch handles btrfs_start_transaction failures that don't occur
>>   in a loop and are obvious to simply push up. In all cases except the
>>   mark_garbage_root case, the error is already handled by BUG_ON in the
>>   caller.
>>
>> Signed-off-by: Jeff Mahoney<jeffm@suse.com>
>> ---
>>   fs/btrfs/extent-tree.c |    6 +++++-
>>   fs/btrfs/relocation.c  |    6 ++++--
>>   fs/btrfs/tree-log.c    |    5 ++++-
>>   fs/btrfs/volumes.c     |    3 ++-
>>   4 files changed, 15 insertions(+), 5 deletions(-)
>>
>> --- a/fs/btrfs/extent-tree.c
>> +++ b/fs/btrfs/extent-tree.c
>> @@ -6319,7 +6319,11 @@ int btrfs_drop_snapshot(struct btrfs_roo
>>   	}
>>
>>   	trans = btrfs_start_transaction(tree_root, 0);
>> -	BUG_ON(IS_ERR(trans));
>> +	if (IS_ERR(trans)) {
>> +		kfree(wc);
>> +		btrfs_free_path(path);
>> +		return PTR_ERR(trans);
>> +	}
> 
> The caller of btrfs_drop_snapshot() ignore the error. So, I don't think
> that it is significant even if the error is returned to the caller.

 I'd actually consider that a separate issue since btrfs_drop_snapshot
also returns -ENOMEM. The errors should be properly caught or BUG_ON'd
in the caller. My patchset usually catches cases like this but since
btrfs_drop_snapshot already returned an error, I mistakenly assumed it
was handled by the caller.

> I think that it should make the filesystem readonly when becoming an error
> in btrfs_start_transaction().

For -ENOMEM, I don't think that's the way to handle it. Some transaction
start failures can be caught and handled (e.g. just creating a file)
easily by returning errors to the user. Other cases, deep in the code,
may be too complex to unwind and recover from and then a ROFS is the
next-best answer. The callers should be responsible for determining the
correct course of action.

-Jeff

> Thanks,
> Tsutomu
> 
>>
>>   	if (block_rsv)
>>   		trans->block_rsv = block_rsv;
>> --- a/fs/btrfs/relocation.c
>> +++ b/fs/btrfs/relocation.c
>> @@ -4096,7 +4096,8 @@ static noinline_for_stack int mark_garba
>>   	int ret;
>>
>>   	trans = btrfs_start_transaction(root->fs_info->tree_root, 0);
>> -	BUG_ON(IS_ERR(trans));
>> +	if (IS_ERR(trans))
>> +		return PTR_ERR(trans);
>>
>>   	memset(&root->root_item.drop_progress, 0,
>>   		sizeof(root->root_item.drop_progress));
>> @@ -4176,7 +4177,8 @@ int btrfs_recover_relocation(struct btrf
>>   					err = ret;
>>   					goto out;
>>   				}
>> -				mark_garbage_root(reloc_root);
>> +				ret = mark_garbage_root(reloc_root);
>> +				BUG_ON(ret);
>>   			}
>>   		}
>>
>> --- a/fs/btrfs/tree-log.c
>> +++ b/fs/btrfs/tree-log.c
>> @@ -3151,7 +3151,10 @@ int btrfs_recover_log_trees(struct btrfs
>>   	fs_info->log_root_recovering = 1;
>>
>>   	trans = btrfs_start_transaction(fs_info->tree_root, 0);
>> -	BUG_ON(IS_ERR(trans));
>> +	if (IS_ERR(trans)) {
>> +		btrfs_free_path(path);
>> +		return PTR_ERR(trans);
>> +	}
>>
>>   	wc.trans = trans;
>>   	wc.pin = 1;
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -1876,7 +1876,8 @@ static int btrfs_relocate_chunk(struct b
>>   		return ret;
>>
>>   	trans = btrfs_start_transaction(root, 0);
>> -	BUG_ON(IS_ERR(trans));
>> +	if (IS_ERR(trans))
>> +		return PTR_ERR(trans);
>>
>>   	lock_chunks(root);
>>
> 


-- 
Jeff Mahoney
SuSE Labs