Hi Liu,
I was studying on how block reservation works, and making some
modifications in reserve_metadata_bytes to understand better what it
does. Then suddenly I saw this problem. I guess it depends on which
value of "flush" parameter is passed to reserve_metadata_bytes.
Alex.
On Thu, Dec 3, 2015 at 8:14 PM, Liu Bo <bo.li....@oracle.com> wrote:
> On Thu, Dec 03, 2015 at 06:51:03PM +0200, Alex Lyakas wrote:
>> do_chunk_alloc returns 1 when it succeeds to allocate a new chunk.
>> But flush_space will not convert this to 0, and will also return 1.
>> As a result, reserve_metadata_bytes will think that flush_space failed,
>> and may potentially return this value "1" to the caller (depends how
>> reserve_metadata_bytes was called). The caller will also treat this as an
>> error.
>> For example, btrfs_block_rsv_refill does:
>>
>> int ret = -ENOSPC;
>> ...
>> ret = reserve_metadata_bytes(root, block_rsv, num_bytes, flush);
>> if (!ret) {
>> block_rsv_add_bytes(block_rsv, num_bytes, 0);
>> return 0;
>> }
>>
>> return ret;
>>
>> So it will return -ENOSPC.
>
> It will return 1 instead of -ENOSPC.
>
> The patch looks good, I noticed this before, but I didn't manage to trigger a
> error for this, did you catch a error like that?
>
> Thanks,
>
> -liubo
>
>>
>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>> index 4b89680..1ba3f0d 100644
>> --- a/fs/btrfs/extent-tree.c
>> +++ b/fs/btrfs/extent-tree.c
>> @@ -4727,7 +4727,7 @@ static int flush_space(struct btrfs_root *root,
>> btrfs_get_alloc_profile(root, 0),
>> CHUNK_ALLOC_NO_FORCE);
>> btrfs_end_transaction(trans, root);
>> - if (ret == -ENOSPC)
>> + if (ret > 0 || ret == -ENOSPC)
>> ret = 0;
>> break;
>> case COMMIT_TRANS:
>> --
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