From: Heinz Mauelshagen <heinzm@redhat.com>
Subject: dm cache policy era: fix spinlock based era_counter increment

FIXME: what exactly was broken?
FIXME: fold into previous era patch

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
---
 drivers/md/dm-cache-policy-era.c |   15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

Index: linux/drivers/md/dm-cache-policy-era.c
===================================================================
--- linux.orig/drivers/md/dm-cache-policy-era.c
+++ linux/drivers/md/dm-cache-policy-era.c
@@ -43,7 +43,6 @@ struct era_policy {
 
 	era_t *cb_to_era;
 
-	spinlock_t era_counter_lock;
 	era_t era_counter;
 };
 
@@ -57,7 +56,6 @@ static struct era_policy *to_era_policy(
 static int incr_era_counter(struct era_policy *era, const char *curr_era_str)
 {
 	era_t curr_era_counter;
-	unsigned long flags;
 	int r;
 
 	/*
@@ -74,19 +72,17 @@ static int incr_era_counter(struct era_p
 	if (kstrtou32(curr_era_str, 10, &curr_era_counter))
 		return -EINVAL;
 
-	spin_lock_irqsave(&era->era_counter_lock, flags);
-
+	smp_rmb();
 	if (era->era_counter != curr_era_counter)
 		r = -ECANCELED;
 	else if (era->era_counter >= ERA_MAX_ERA)
 		r = -EOVERFLOW;
 	else {
 		era->era_counter++;
+		smp_wmb();
 		r = 0;
 	}
 
-	spin_unlock_irqrestore(&era->era_counter_lock, flags);
-
 	return r;
 }
 
@@ -231,6 +227,7 @@ static int era_map(struct dm_cache_polic
 	if (!r && (bio_data_dir(bio) == WRITE) && (result->op == POLICY_HIT)) {
 		cb_idx = from_cblock(result->cblock);
 		BUG_ON(cb_idx >= from_cblock(era->cache_size));
+		smp_rmb();
 #if DEBUG_ERA
 		DMDEBUG("assigning era %u to cblock %u, oblock %llu due to write hit.",
 			era->era_counter, result->cblock, oblock);
@@ -272,10 +269,12 @@ static int era_load_mapping(struct dm_ca
 		 * Make sure the era counter starts higher than the highest
 		 * persisted era.
 		 */
+		smp_rmb();
 		if (recovered_era >= era->era_counter) {
 			era->era_counter = recovered_era;
 			if (era->era_counter < ERA_MAX_ERA)
 				era->era_counter++;
+			smp_wmb();
 #if DEBUG_ERA
 			DMDEBUG("set era_counter to %u.", era->era_counter);
 #endif
@@ -300,6 +299,7 @@ static void era_force_mapping(struct dm_
 	mutex_lock(&era->lock);
 
 	if (!policy_lookup(p->child, old_oblock, &cblock)) {
+		smp_rmb();
 #if DEBUG_ERA
 		DMDEBUG("assigning era %u to cblock %u, oblock %llu "
 			"(old_oblock %llu) due to force_mapping.",
@@ -340,6 +340,8 @@ static int era_emit_config_values(struct
 {
 	struct era_policy *era = to_era_policy(p);
 	ssize_t sz = 0;
+
+	smp_rmb();
 	DMEMIT("era_counter %u ", era->era_counter);
 	return policy_emit_config_values(p->child, result + sz, maxlen - sz);
 }
@@ -369,7 +371,6 @@ static struct dm_cache_policy *era_creat
 	init_policy_functions(era);
 	era->cache_size = cache_size;
 	mutex_init(&era->lock);
-	spin_lock_init(&era->era_counter_lock);
 
 	era->cb_to_era = kzalloc(from_cblock(era->cache_size) *
 				 sizeof(*(era->cb_to_era)), GFP_KERNEL);