btrfs: rename member 'trimming' of block group to a more generic name

Back in 2014, commit 04216820fe83d5 ("Btrfs: fix race between fs trimming
and block group remove/allocation"), I added the 'trimming' member to the
block group structure. Its purpose was to prevent races between trimming
and block group deletion/allocation by pinning the block group in a way
that prevents its logical address and device extents from being reused
while trimming is in progress for a block group, so that if another task
deletes the block group and then another task allocates a new block group
that gets the same logical address and device extents while the trimming
task is still in progress.

After the previous fix for scrub (patch "btrfs: fix a race between scrub
and block group removal/allocation"), scrub now also has the same needs that
trimming has, so the member name 'trimming' no longer makes sense.
Since there is already a 'pinned' member in the block group that refers
to space reservations (pinned bytes), rename the member to 'frozen',
add a comment on top of it to describe its general purpose and rename
the helpers to increment and decrement the counter as well, to match
the new member name.

The next patch in the series will move the helpers into a more suitable
file (from free-space-cache.c to block-group.c).

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/fs/btrfs/block-group.h b/fs/btrfs/block-group.h
index 107bb557ca8d..04967ea7ba2c 100644
--- a/fs/btrfs/block-group.h
+++ b/fs/btrfs/block-group.h
@@ -129,8 +129,17 @@ struct btrfs_block_group {
 	/* For read-only block groups */
 	struct list_head ro_list;
 
+	/*
+	 * When non-zero it means the block group's logical address and its
+	 * device extents can not be reused for future block group allocations
+	 * until the counter goes down to 0. This is to prevent them from being
+	 * reused while some task is still using the block group after it was
+	 * deleted - we want to make sure they can only be reused for new block
+	 * groups after that task is done with the deleted block group.
+	 */
+	atomic_t frozen;
+
 	/* For discard operations */
-	atomic_t trimming;
 	struct list_head discard_list;
 	int discard_index;
 	u64 discard_eligible_time;