Re: [PATCH 01/13] lightnvm: pblk: Line reference fix in GC

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On Wed, Feb 27, 2019 at 6:17 PM Igor Konopko <igor.j.konopko@xxxxxxxxx> wrote:
>
> This patch fixes the error case in GC when
> we both moves line back to closed state and
> release additional reference, what cause illegal
> transition from closed to free on pblk_line_put
> when only gc to free line state transition is
> allowed using that path.
>
> Signed-off-by: Igor Konopko <igor.j.konopko@xxxxxxxxx>
> ---
>  drivers/lightnvm/pblk-gc.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/lightnvm/pblk-gc.c b/drivers/lightnvm/pblk-gc.c
> index 2fa118c8eb71..3feadfd9418d 100644
> --- a/drivers/lightnvm/pblk-gc.c
> +++ b/drivers/lightnvm/pblk-gc.c
> @@ -290,8 +290,11 @@ static void pblk_gc_line_prepare_ws(struct work_struct *work)
>  fail_free_ws:
>         kfree(line_ws);
>
> +       /* Line goes back to closed state, so we cannot release additional
> +        * reference for line, since we do that only when we want to do
> +        * gc to free line state transition.
> +        */

Good comment.
It would be nice to document how the line recounting works in general,
as it is, non-trivial to deduce from the code.
I dug into this when supporting Heiner in his latest bugfix, and it's
on my laundry list .. but if someone else feels inclined.. :)

>         pblk_put_line_back(pblk, line);
> -       kref_put(&line->ref, pblk_line_put);
>         atomic_dec(&gc->read_inflight_gc);
>
>         pblk_err(pblk, "failed to GC line %d\n", line->id);
> --
> 2.17.1
>

Great catch!
Reviewed-by: Hans Holmberg <hans.holmberg@xxxxxxxxxxxx>



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