pblk: fix max_io calculation

When calculating the maximun I/O size allowed into the buffer, consider
the write size (ws_opt) used by the write thread in order to cover the
case in which, due to flushes, the mem and subm pointers are disaligned
by (ws_opt - 1). This case currently translates into a stall when
an I/O of the largest possible size is submitted.

Fixes: f9f9d1ae2c66 ("lightnvm: pblk: prevent stall due to wb threshold")

Signed-off-by: Javier González <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/lightnvm/pblk-rl.c

···
 	/* To start with, all buffer is available to user I/O writers */
 	rl->rb_budget = budget;
 	rl->rb_user_max = budget;
-	rl->rb_max_io = threshold ? (budget - threshold) : (budget - 1);
 	rl->rb_gc_max = 0;
 	rl->rb_state = PBLK_RL_HIGH;
+
+	/* Maximize I/O size and ansure that back threshold is respected */
+	if (threshold)
+		rl->rb_max_io = budget - pblk->min_write_pgs_data - threshold;
+	else
+		rl->rb_max_io = budget - pblk->min_write_pgs_data - 1;
 
 	atomic_set(&rl->rb_user_cnt, 0);
 	atomic_set(&rl->rb_gc_cnt, 0);