Re: [PATCH 03/13] lightnvm: pblk: Fix put line back behaviour

["Javier González" <javier@javigon.com>]

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> On 27 Feb 2019, at 18.14, Igor Konopko <igor.j.konopko@intel.com> wrote:
> 
> In current implementation of pblk_put_line_back behaviour
> there are two cases which are not handled.
> 
> First one is the race condition with __pblk_map_invalidate in
> which function we check for line state, which might be closed,
> but still not added to any list and thus explode in list_move_tail.
> This is due to lack of locking both gc_lock and line lock
> in pblk_put_line_back current implementation.
> 
> The second issue is that when we are in that function, line
> is not on any list and pblk_line_gc_list might hit the same
> gc group and thus not return any move_list. Then our line
> will stuck forever unassigned to any list. Simply resetting
> gc_list to none will fix that.
> 
> Signed-off-by: Igor Konopko <igor.j.konopko@intel.com>
> ---
> drivers/lightnvm/pblk-gc.c | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/lightnvm/pblk-gc.c b/drivers/lightnvm/pblk-gc.c
> index 31fc1339faa8..511ed0d5333c 100644
> --- a/drivers/lightnvm/pblk-gc.c
> +++ b/drivers/lightnvm/pblk-gc.c
> @@ -64,19 +64,23 @@ static void pblk_put_line_back(struct pblk *pblk, struct pblk_line *line)
> 	struct pblk_line_mgmt *l_mg = &pblk->l_mg;
> 	struct list_head *move_list;
> 
> +	spin_lock(&l_mg->gc_lock);
> 	spin_lock(&line->lock);
> 	WARN_ON(line->state != PBLK_LINESTATE_GC);
> 	line->state = PBLK_LINESTATE_CLOSED;
> 	trace_pblk_line_state(pblk_disk_name(pblk), line->id,
> 					line->state);
> +
> +	/* We need to reset gc_group in order to ensure that
> +	 * pblk_line_gc_list will return proper move_list
> +	 * since right now current line is not on any of the
> +	 * gc lists.
> +	 */
> +	line->gc_group = PBLK_LINEGC_NONE;
> 	move_list = pblk_line_gc_list(pblk, line);
> 	spin_unlock(&line->lock);
> -
> -	if (move_list) {
> -		spin_lock(&l_mg->gc_lock);
> -		list_add_tail(&line->list, move_list);
> -		spin_unlock(&l_mg->gc_lock);
> -	}
> +	list_add_tail(&line->list, move_list);
> +	spin_unlock(&l_mg->gc_lock);
> }
> 
> static void pblk_gc_line_ws(struct work_struct *work)
> --
> 2.17.1

This comes back from the time where GC was single threaded - I left out
this when reimplementing the locking. Good catch.

Please, add a fixes tag for this to be back ported.

Reviewed-by: Javier González <javier@javigon.com>


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