lightnvm: pblk: fail gracefully on irrec. error

Due to user writes being decoupled from media writes because of the need
of an intermediate write buffer, irrecoverable media write errors lead
to pblk stalling; user writes fill up the buffer and end up in an
infinite retry loop.

In order to let user writes fail gracefully, it is necessary for pblk to
keep track of its own internal state and prevent further writes from
being placed into the write buffer.

This patch implements a state machine to keep track of internal errors
and, in case of failure, fail further user writes in an standard way.
Depending on the type of error, pblk will do its best to persist
buffered writes (which are already acknowledged) and close down on a
graceful manner. This way, data might be recovered by re-instantiating
pblk. Such state machine paves out the way for a state-based FTL log.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <matias@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 28 insertions, 2 deletions

diff --git a/drivers/lightnvm/pblk-rl.c b/drivers/lightnvm/pblk-rl.c
index 52068a1807a8..2e6a5361baf0 100644
--- a/drivers/lightnvm/pblk-rl.c
+++ b/drivers/lightnvm/pblk-rl.c
@@ -23,11 +23,35 @@ static void pblk_rl_kick_u_timer(struct pblk_rl *rl)
 	mod_timer(&rl->u_timer, jiffies + msecs_to_jiffies(5000));
 }
 
+int pblk_rl_is_limit(struct pblk_rl *rl)
+{
+	int rb_space;
+
+	rb_space = atomic_read(&rl->rb_space);
+
+	return (rb_space == 0);
+}
+
 int pblk_rl_user_may_insert(struct pblk_rl *rl, int nr_entries)
 {
 	int rb_user_cnt = atomic_read(&rl->rb_user_cnt);
+	int rb_space = atomic_read(&rl->rb_space);
+
+	if (unlikely(rb_space >= 0) && (rb_space - nr_entries < 0))
+		return NVM_IO_ERR;
+
+	if (rb_user_cnt >= rl->rb_user_max)
+		return NVM_IO_REQUEUE;
 
-	return (!(rb_user_cnt >= rl->rb_user_max));
+	return NVM_IO_OK;
+}
+
+void pblk_rl_inserted(struct pblk_rl *rl, int nr_entries)
+{
+	int rb_space = atomic_read(&rl->rb_space);
+
+	if (unlikely(rb_space >= 0))
+		atomic_sub(nr_entries, &rl->rb_space);
 }
 
 int pblk_rl_gc_may_insert(struct pblk_rl *rl, int nr_entries)
@@ -190,10 +214,12 @@ void pblk_rl_init(struct pblk_rl *rl, int budget)
 	/* To start with, all buffer is available to user I/O writers */
 	rl->rb_budget = budget;
 	rl->rb_user_max = budget;
-	atomic_set(&rl->rb_user_cnt, 0);
 	rl->rb_gc_max = 0;
 	rl->rb_state = PBLK_RL_HIGH;
+
+	atomic_set(&rl->rb_user_cnt, 0);
 	atomic_set(&rl->rb_gc_cnt, 0);
+	atomic_set(&rl->rb_space, -1);
 
 	setup_timer(&rl->u_timer, pblk_rl_u_timer, (unsigned long)rl);