From 1e72a8e809f030bd4e318a49c497ee38e47e82c1 Mon Sep 17 00:00:00 2001
From: Joe Thornber <ejt@redhat.com>
Date: Wed, 8 Nov 2017 05:56:11 -0500
Subject: [PATCH] dm cache policy smq: handle races with queuing
 background_work
Git-commit: 1e72a8e809f030bd4e318a49c497ee38e47e82c1
Patch-mainline: v4.15-rc1
References: bsc#1093023

The background_tracker holds a set of promotions/demotions that the
cache policy wishes the core target to implement.

When adding a new operation to the tracker it's possible that an
operation on the same block is already present (but in practise this
doesn't appear to be happening).  Catch these situations and do the
appropriate cleanup.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Coly Li <colyli@suse.de>

---
 drivers/md/dm-cache-policy-smq.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-cache-policy-smq.c b/drivers/md/dm-cache-policy-smq.c
index e5eb9c9b4bc8..42e5c4b59889 100644
--- a/drivers/md/dm-cache-policy-smq.c
+++ b/drivers/md/dm-cache-policy-smq.c
@@ -1174,12 +1174,16 @@ static void queue_writeback(struct smq_policy *mq)
 		work.cblock = infer_cblock(mq, e);
 
 		r = btracker_queue(mq->bg_work, &work, NULL);
-		WARN_ON_ONCE(r); // FIXME: finish, I think we have to get rid of this race.
+		if (r) {
+			clear_pending(mq, e);
+			q_push_front(&mq->dirty, e);
+		}
 	}
 }
 
 static void queue_demotion(struct smq_policy *mq)
 {
+	int r;
 	struct policy_work work;
 	struct entry *e;
 
@@ -1199,12 +1203,17 @@ static void queue_demotion(struct smq_policy *mq)
 	work.op = POLICY_DEMOTE;
 	work.oblock = e->oblock;
 	work.cblock = infer_cblock(mq, e);
-	btracker_queue(mq->bg_work, &work, NULL);
+	r = btracker_queue(mq->bg_work, &work, NULL);
+	if (r) {
+		clear_pending(mq, e);
+		q_push_front(&mq->clean, e);
+	}
 }
 
 static void queue_promotion(struct smq_policy *mq, dm_oblock_t oblock,
 			    struct policy_work **workp)
 {
+	int r;
 	struct entry *e;
 	struct policy_work work;
 
@@ -1234,7 +1243,9 @@ static void queue_promotion(struct smq_policy *mq, dm_oblock_t oblock,
 	work.op = POLICY_PROMOTE;
 	work.oblock = oblock;
 	work.cblock = infer_cblock(mq, e);
-	btracker_queue(mq->bg_work, &work, workp);
+	r = btracker_queue(mq->bg_work, &work, workp);
+	if (r)
+		free_entry(&mq->cache_alloc, e);
 }
 
 /*----------------------------------------------------------------*/
-- 
2.16.3