On Thu, Apr 5, 2018 at 9:48 AM, David Sterba <dsterba@xxxxxxx> wrote:
> On Sat, Mar 31, 2018 at 06:11:55AM +0800, Liu Bo wrote:
>> This is running in a typical write path, not inside a critical path
>> where we have to abort the running transaction, so it's OK to return
>> errors to callers and eventually to userspace.
>
> I'm not sure this is entierly correct, several other places do not abort
> after btrfs_drop_extents as there's nothing that would leave the
> structres in some half-state.
>
>> Signed-off-by: Liu Bo <bo.liu@xxxxxxxxxxxxxxxxx>
>> ---
>> fs/btrfs/inode.c | 5 +----
>> 1 file changed, 1 insertion(+), 4 deletions(-)
>>
>> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
>> index c7b75dd..b9310f8 100644
>> --- a/fs/btrfs/inode.c
>> +++ b/fs/btrfs/inode.c
>> @@ -4939,16 +4939,13 @@ static int maybe_insert_hole(struct btrfs_root *root, struct inode *inode,
>>
>> ret = btrfs_drop_extents(trans, root, inode, offset, offset + len, 1);
>> if (ret) {
>> - btrfs_abort_transaction(trans, ret);
>> btrfs_end_transaction(trans);
>> return ret;
>> }
>>
>> ret = btrfs_insert_file_extent(trans, root, btrfs_ino(BTRFS_I(inode)),
>> offset, 0, 0, len, 0, len, 0, 0, 0);
>
> But here the extents have been already dropped and missing to insert the
> items does not seem to lead to a consistent state.
>
> It's possible that I'm missing something. In a call path that can be
> safely rolled back even with a started transaction, we don't need to
> abort in all cases. But if the rollback requires some non-trivial
> modifications, I don't see options how to avoid the abort.
>
> __btrfs_drop_extents does a lot of state changes and can itself fail
> in the middle of dropping the range, aborting looks like the safest
> option.
>
As maybe_insert_hole is only called by btrfs_cont_expand here, which
means it's a really hole, I don't expect drop_extents would drop
anything, we can remove this drop_extents and put an assert after
btrfs_insert_file_extent for checking EEXIST.
It's different from punch hole where we need to explicitly drop an
actual extent and replace it with a hole range.
thanks,
liubo
>> - if (ret)
>> - btrfs_abort_transaction(trans, ret);
>> - else
>> + if (!ret)
>> btrfs_update_inode(trans, root, inode);
>> btrfs_end_transaction(trans);
>> return ret;
> --
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