Re: [PATCH 4/5] btrfs: dont clear qgroup rsv bit in release_folio

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2023/12/2 07:30, Boris Burkov wrote:
> The EXTENT_QGROUP_RESERVED bit is used to "lock" regions of the file for
> duplicate reservations. That is two writes to that range in one
> transaction shouldn't create two reservations, as the reservation will
> only be freed once when the write finally goes down. Therefore, it is
> never OK to clear that bit without freeing the associated qgroup rsv. At
> this point, we don't want to be freeing the rsv, so mask off the bit.

Did you have any dmesg output for this case? I believe this would lead
to a underflow.
>
> Signed-off-by: Boris Burkov <boris@bur.io>

Reviewed-by: Qu Wenruo <wqu@suse.com>

Thanks,
Qu
> ---
>   fs/btrfs/extent_io.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index 0143bf63044c..87283087c669 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -2310,7 +2310,8 @@ static int try_release_extent_state(struct extent_io_tree *tree,
>   		ret = 0;
>   	} else {
>   		u32 clear_bits = ~(EXTENT_LOCKED | EXTENT_NODATASUM |
> -				   EXTENT_DELALLOC_NEW | EXTENT_CTLBITS);
> +				   EXTENT_DELALLOC_NEW | EXTENT_CTLBITS
> +				   | EXTENT_QGROUP_RESERVED);
>
>   		/*
>   		 * At this point we can safely clear everything except the