From 29566c9c773456467933ee22bbca1c2b72a3506c Mon Sep 17 00:00:00 2001 From: Madhuparna Bhowmik Date: Fri, 6 Mar 2020 12:22:43 +0530 Subject: [PATCH] btrfs: add RCU locks around block group initialization The space_info list is normally RCU protected and should be traversed with rcu_read_lock held. There's a warning [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!! pointing out that the locking is missing in btrfs_read_block_groups. However this is not necessary as the list traversal happens at mount time when there's no other thread potentially accessing the list. To fix the warning and for consistency let's add the RCU lock/unlock, the code won't be affected much as it's doing some lightweight operations. Reported-by: Guenter Roeck Signed-off-by: Madhuparna Bhowmik Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/block-group.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c index b8f39a679064..786849fcc319 100644 --- a/fs/btrfs/block-group.c +++ b/fs/btrfs/block-group.c @@ -2008,6 +2008,7 @@ 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 | @@ -2028,6 +2029,7 @@ 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);