From: Hans Holmberg <hans.holmberg@cnexlabs.com>
Date: Fri, 30 Mar 2018 00:04:58 +0200
Subject: [PATCH] lightnvm: pblk: prevent race in pblk_rb_flush_point_set
Git-commit: 3c05ef115c696392d9703be3fe014100ec77864d
Patch-mainline: v4.17-rc1
References: bsc#1104967,FATE#325924
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Make sure that we are not advancing the sync pointer while
we're adding bios to the write buffer entry completion list.

This race condition results in bios not completing and was identified
by a hang when running xfstest generic/113.

Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Reviewed-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 drivers/lightnvm/pblk-rb.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/lightnvm/pblk-rb.c b/drivers/lightnvm/pblk-rb.c
index 8b1434060fb3..52fdd85dbc97 100644
--- a/drivers/lightnvm/pblk-rb.c
+++ b/drivers/lightnvm/pblk-rb.c
@@ -355,10 +355,13 @@ static int pblk_rb_flush_point_set(struct pblk_rb *rb, struct bio *bio,
 	struct pblk_rb_entry *entry;
 	unsigned int sync, flush_point;
 
+	pblk_rb_sync_init(rb, NULL);
 	sync = READ_ONCE(rb->sync);
 
-	if (pos == sync)
+	if (pos == sync) {
+		pblk_rb_sync_end(rb, NULL);
 		return 0;
+	}
 
 #ifdef CONFIG_NVM_DEBUG
 	atomic_inc(&rb->inflight_flush_point);
@@ -367,8 +370,6 @@ static int pblk_rb_flush_point_set(struct pblk_rb *rb, struct bio *bio,
 	flush_point = (pos == 0) ? (rb->nr_entries - 1) : (pos - 1);
 	entry = &rb->entries[flush_point];
 
-	pblk_rb_sync_init(rb, NULL);
-
 	/* Protect flush points */
 	smp_store_release(&rb->flush_point, flush_point);
 
-- 
2.12.3