[PATCH] fs: btrfs: block-group.c: Fix suspicious RCU usage warning

[madhuparnabhowmik10]

From: Madhuparna Bhowmik <madhuparnabhowmik10@xxxxxxxxx>

The space_info list is rcu protected.
Hence, it should be traversed with rcu_read_lock held.

Warning:
[   29.104591] =============================
[   29.104756] WARNING: suspicious RCU usage
[   29.105046] 5.6.0-rc4-next-20200305 #1 Not tainted
[   29.105231] -----------------------------
[   29.105401] fs/btrfs/block-group.c:2011 RCU-list traversed in non-reader section!!

Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@xxxxxxxxx>
---
 fs/btrfs/block-group.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 404e050ce8ee..9cabeef66f5b 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1987,6 +1987,7 @@ int btrfs_read_block_groups(struct btrfs_fs_info *info)
 		btrfs_release_path(path);
 	}
 
+	rcu_read_lock();
 	list_for_each_entry_rcu(space_info, &info->space_info, list) {
 		if (!(btrfs_get_alloc_profile(info, space_info->flags) &
 		      (BTRFS_BLOCK_GROUP_RAID10 |
@@ -2007,7 +2008,8 @@ int btrfs_read_block_groups(struct btrfs_fs_info *info)
 				list)
 			inc_block_group_ro(cache, 1);
 	}
-
+	rcu_read_unlock();
+		
 	btrfs_init_global_block_rsv(info);
 	ret = check_chunk_block_group_mappings(info);
 error:
-- 
2.17.1