Re: [PATCH 3/8] btrfs: explicitly protect ->last_byte_to_unpin in unpin_extent_range

[Filipe Manana <fdmanana@gmail.com>]

On Fri, Oct 23, 2020 at 5:12 PM Josef Bacik <josef@toxicpanda.com> wrote:
>
> Currently unpin_extent_range happens in the transaction commit context,
> so we are protected from ->last_byte_to_unpin changing while we're
> unpinning, because any new transactions would have to wait for us to
> complete before modifying ->last_byte_to_unpin.
>
> However in the future we may want to change how this works, for instance
> with async unpinning or other such TODO items.  To prepare for that
> future explicitly protect ->last_byte_to_unpin with the commit_root_sem
> so we are sure it won't change while we're doing our work.
>
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

Reviewed-by: Filipe Manana <fdmanana@suse.com>

Ok, looks good, thanks.

> ---
>  fs/btrfs/extent-tree.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index ee7bceace8b3..5d3564b077bf 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -2791,11 +2791,13 @@ static int unpin_extent_range(struct btrfs_fs_info *fs_info,
>                 len = cache->start + cache->length - start;
>                 len = min(len, end + 1 - start);
>
> +               down_read(&fs_info->commit_root_sem);
>                 if (start < cache->last_byte_to_unpin && return_free_space) {
>                         u64 add_len = min(len,
>                                           cache->last_byte_to_unpin - start);
>                         btrfs_add_free_space(cache, start, add_len);
>                 }
> +               up_read(&fs_info->commit_root_sem);
>
>                 start += len;
>                 total_unpinned += len;
> --
> 2.26.2
>


-- 
Filipe David Manana,

“Whether you think you can, or you think you can't — you're right.”