> On 14 Mar 2019, at 17.04, Igor Konopko <igor.j.konopko@intel.com> wrote:
> 
> When we are trying to switch to the new line, we need to ensure that
> emeta for n-2 line is already written. In other case we can end with
> deadlock scenario, when the writer has no more requests to write and
> thus there is no way to trigger emeta writes from writer thread. This
> is a corner case scenario which occurs in a case of multiple writes
> error and thus kind of early line close due to lack of line space.
> 
> Signed-off-by: Igor Konopko <igor.j.konopko@intel.com>
> ---
> drivers/lightnvm/pblk-core.c  |  2 ++
> drivers/lightnvm/pblk-write.c | 24 ++++++++++++++++++++++++
> drivers/lightnvm/pblk.h       |  1 +
> 3 files changed, 27 insertions(+)
> 
> diff --git a/drivers/lightnvm/pblk-core.c b/drivers/lightnvm/pblk-core.c
> index 38e26fe..a683d1f 100644
> --- a/drivers/lightnvm/pblk-core.c
> +++ b/drivers/lightnvm/pblk-core.c
> @@ -1001,6 +1001,7 @@ static void pblk_line_setup_metadata(struct pblk_line *line,
> 				     struct pblk_line_mgmt *l_mg,
> 				     struct pblk_line_meta *lm)
> {
> +	struct pblk *pblk = container_of(l_mg, struct pblk, l_mg);
> 	int meta_line;
> 
> 	lockdep_assert_held(&l_mg->free_lock);
> @@ -1009,6 +1010,7 @@ static void pblk_line_setup_metadata(struct pblk_line *line,
> 	meta_line = find_first_zero_bit(&l_mg->meta_bitmap, PBLK_DATA_LINES);
> 	if (meta_line == PBLK_DATA_LINES) {
> 		spin_unlock(&l_mg->free_lock);
> +		pblk_write_emeta_force(pblk);
> 		io_schedule();
> 		spin_lock(&l_mg->free_lock);
> 		goto retry_meta;
> diff --git a/drivers/lightnvm/pblk-write.c b/drivers/lightnvm/pblk-write.c
> index 4e63f9b..4fbb9b2 100644
> --- a/drivers/lightnvm/pblk-write.c
> +++ b/drivers/lightnvm/pblk-write.c
> @@ -505,6 +505,30 @@ static struct pblk_line *pblk_should_submit_meta_io(struct pblk *pblk,
> 	return meta_line;
> }
> 
> +void pblk_write_emeta_force(struct pblk *pblk)
> +{
> +	struct pblk_line_meta *lm = &pblk->lm;
> +	struct pblk_line_mgmt *l_mg = &pblk->l_mg;
> +	struct pblk_line *meta_line;
> +
> +	while (true) {
> +		spin_lock(&l_mg->close_lock);
> +		if (list_empty(&l_mg->emeta_list)) {
> +			spin_unlock(&l_mg->close_lock);
> +			break;
> +		}
> +		meta_line = list_first_entry(&l_mg->emeta_list,
> +						struct pblk_line, list);
> +		if (meta_line->emeta->mem >= lm->emeta_len[0]) {
> +			spin_unlock(&l_mg->close_lock);
> +			io_schedule();
> +			continue;
> +		}
> +		spin_unlock(&l_mg->close_lock);
> +		pblk_submit_meta_io(pblk, meta_line);
> +	}
> +}
> +
> static int pblk_submit_io_set(struct pblk *pblk, struct nvm_rq *rqd)
> {
> 	struct ppa_addr erase_ppa;
> diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h
> index 0a85990..a42bbfb 100644
> --- a/drivers/lightnvm/pblk.h
> +++ b/drivers/lightnvm/pblk.h
> @@ -877,6 +877,7 @@ int pblk_write_ts(void *data);
> void pblk_write_timer_fn(struct timer_list *t);
> void pblk_write_should_kick(struct pblk *pblk);
> void pblk_write_kick(struct pblk *pblk);
> +void pblk_write_emeta_force(struct pblk *pblk);
> 
> /*
>  * pblk read path
> --
> 2.9.5

This should not be possible. In pblk_map_page_data() we wait to close
emeta for the previous line before starting to write to the new line
(look at pblk_line_close_meta(). Note that we schedule emeta writes for
the previous line as we write the current line, so this function is only
called in extreme cases. Otherwise, this would show jittering.

Do you have a different case in mind?