Re: [PATCH 10/18] lightnvm: pblk: ensure that emeta is written

["Matias Bjørling" <mb@lightnvm.io>]

On 3/14/19 9:04 AM, Igor Konopko 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
> 

Hi Igor,

Is this an error that qemu can force pblk to expose? Can you provide a 
specific example on what is needed to force the error?