Re: [PATCH 1/2] btrfs-progs: check: run delayed refs after writing out dirty block groups

[Jeff Mahoney <jeffm@suse.com>]

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On 4/2/19 3:19 PM, Filipe Manana wrote:
> On Tue, Apr 2, 2019 at 7:29 PM <jeffm@suse.com> wrote:
>>
>> From: Jeff Mahoney <jeffm@suse.com>
>>
>> When repairing the extent tree, it's possible for delayed extents to
>> be created when running btrfs_write_dirty_block_groups.  We run
>> delayed refs one last time in the kernel but that is missing in
>> the userspace tools.
>>
>> That results in delayed refs getting dropped on the floor, the extent
>> records not getting created, and in the next tranaction, when the
>> extent tree is CoW'd again, we hit the BUG_ON when we can't find
>> the extent record.
>>
>> We can fix this by running the delayed refs after writing out the
>> dirty block groups.
>>
>> Signed-off-by: Jeff Mahoney <jeffm@suse.com>
>> ---
>>  transaction.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/transaction.c b/transaction.c
>> index e756db33..2f19e9c8 100644
>> --- a/transaction.c
>> +++ b/transaction.c
>> @@ -194,6 +194,8 @@ commit_tree:
>>         ret = btrfs_run_delayed_refs(trans, -1);
>>         BUG_ON(ret);
>>         btrfs_write_dirty_block_groups(trans);
>> +       ret = btrfs_run_delayed_refs(trans, -1);
>> +       BUG_ON(ret);
> 
> And running delayed refs can dirty more block groups as well.
> At this point shouldn't we loop running delayed refs until no more
> dirty block groups exist? Just like in the kernel.

Right.  This is another argument for code sharing between the kernel and
userspace.

-Jeff

> thanks
> 
>>         __commit_transaction(trans, root);
>>         if (ret < 0)
>>                 goto out;
>> --
>> 2.16.4
>>
> 
> 


-- 
Jeff Mahoney
SUSE Labs


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