Commit 29566c9c authored Mar 06, 2020 by Madhuparna Bhowmik Committed by David Sterba Mar 23, 2020

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 <linux@roeck-us.net>
Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent 65cd6d9e

fs/btrfs/block-group.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -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);

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