From: Jeff Moyer <jmoyer@redhat.com>
Date: Wed, 13 Dec 2017 16:33:09 -0500
Subject: [PATCH 3/3] libnvdimm, btt: fix uninitialized err_lock
Patch-mainline: v4.16-rc1
Git-commit: d08cd5e0eb632eef7819ba911c09d89a767f2d0c
References: bsc#1103961

When a sector mode namespace is initially created, the arena's err_lock
is not initialized.  If, on the other hand, the namespace already
exists, the mutex is initialized.  To fix the issue, I moved the mutex
initialization into the arena_alloc, which is called by both
discover_arenas and create_arenas.

This was discovered on an older kernel where mutex_trylock checks the
count to determine whether the lock is held.  Because the data structure
is kzalloc-d, that count was 0 (held), and I/O to the device would hang
forever waiting for the lock to be released (see btt_write_pg, for
example).  Current kernels have a different mutex implementation that
checks for a non-null owner, and so this doesn't show up as a problem.
If that lock were ever contended, it might cause issues, but you'd have
to be really unlucky, I think.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
---
 drivers/nvdimm/btt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c
index 67c6b2dfce18..1a882465fffd 100644
--- a/drivers/nvdimm/btt.c
+++ b/drivers/nvdimm/btt.c
@@ -752,6 +752,7 @@ static struct arena_info *alloc_arena(struct btt *btt, size_t size,
 		return NULL;
 	arena->nd_btt = btt->nd_btt;
 	arena->sector_size = btt->sector_size;
+	mutex_init(&arena->err_lock);
 
 	if (!size)
 		return arena;
@@ -890,7 +891,6 @@ static int discover_arenas(struct btt *btt)
 			goto out;
 		}
 
-		mutex_init(&arena->err_lock);
 		ret = btt_freelist_init(arena);
 		if (ret)
 			goto out;
-- 
2.12.3