Re: [PATCH v2 08/12] btrfs: make lock_and_cleanup_extent_if_need nowait compatible

[Filipe Manana <fdmanana@kernel.org>]

On Thu, Sep 8, 2022 at 1:26 AM Stefan Roesch <shr@fb.com> wrote:
>
> This adds the nowait parameter to lock_and_cleanup_extent_if_need(). If
> the nowait parameter is specified we try to lock the extent in nowait
> mode.
>
> Signed-off-by: Stefan Roesch <shr@fb.com>
> ---
>  fs/btrfs/file.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index a154a3cec44b..4e1745e585cb 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1440,7 +1440,7 @@ static noinline int
>  lock_and_cleanup_extent_if_need(struct btrfs_inode *inode, struct page **pages,
>                                 size_t num_pages, loff_t pos,
>                                 size_t write_bytes,
> -                               u64 *lockstart, u64 *lockend,
> +                               u64 *lockstart, u64 *lockend, bool nowait,
>                                 struct extent_state **cached_state)
>  {
>         struct btrfs_fs_info *fs_info = inode->root->fs_info;
> @@ -1455,8 +1455,20 @@ lock_and_cleanup_extent_if_need(struct btrfs_inode *inode, struct page **pages,
>         if (start_pos < inode->vfs_inode.i_size) {
>                 struct btrfs_ordered_extent *ordered;
>
> -               lock_extent_bits(&inode->io_tree, start_pos, last_pos,
> +               if (nowait) {
> +                       if (!try_lock_extent(&inode->io_tree, start_pos, last_pos)) {
> +                               for (i = 0; i < num_pages; i++) {
> +                                       unlock_page(pages[i]);
> +                                       put_page(pages[i]);

Since this is a non-local array, I'd prefer if we also set pages[i] to NULL.
That may help prevent hard to debug bugs in the future.

Thanks.


> +                               }
> +
> +                               return -EAGAIN;
> +                       }
> +               } else {
> +                       lock_extent_bits(&inode->io_tree, start_pos, last_pos,
>                                 cached_state);
> +               }
> +
>                 ordered = btrfs_lookup_ordered_range(inode, start_pos,
>                                                      last_pos - start_pos + 1);
>                 if (ordered &&
> @@ -1755,7 +1767,7 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
>                 extents_locked = lock_and_cleanup_extent_if_need(
>                                 BTRFS_I(inode), pages,
>                                 num_pages, pos, write_bytes, &lockstart,
> -                               &lockend, &cached_state);
> +                               &lockend, false, &cached_state);
>                 if (extents_locked < 0) {
>                         if (extents_locked == -EAGAIN)
>                                 goto again;
> --
> 2.30.2
>