From 1cfc4552917a128e0cdf15f57abfe60a30f5eaec Mon Sep 17 00:00:00 2001 From: Joe Thornber Date: Fri, 13 Dec 2013 14:55:55 +0000 Subject: [PATCH] dm array: fix a reference counting bug in shadow_ablock commit ed9571f0cf1fe09d3506302610f3ccdfa1d22c4a upstream. An old array block could have its reference count decremented below zero when it is being replaced in the btree by a new array block. The fix is to increment the old ablock's reference count just before inserting a new ablock into the btree. Signed-off-by: Joe Thornber Signed-off-by: Mike Snitzer Signed-off-by: Greg Kroah-Hartman --- drivers/md/persistent-data/dm-array.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/drivers/md/persistent-data/dm-array.c b/drivers/md/persistent-data/dm-array.c index af96e24..1d75b1d 100644 --- a/drivers/md/persistent-data/dm-array.c +++ b/drivers/md/persistent-data/dm-array.c @@ -317,8 +317,16 @@ static int shadow_ablock(struct dm_array_info *info, dm_block_t *root, * The shadow op will often be a noop. Only insert if it really * copied data. */ - if (dm_block_location(*block) != b) + if (dm_block_location(*block) != b) { + /* + * dm_tm_shadow_block will have already decremented the old + * block, but it is still referenced by the btree. We + * increment to stop the insert decrementing it below zero + * when overwriting the old value. + */ + dm_tm_inc(info->btree_info.tm, b); r = insert_ablock(info, index, *block, root); + } return r; } -- 2.7.4