From ae4477f937569d097ca5dbce92a89ba384b49bc6 Mon Sep 17 00:00:00 2001 From: Mark Harmstone Date: Thu, 29 May 2025 10:37:44 +0100 Subject: [PATCH] btrfs: update superblock's device bytes_used when dropping chunk Each superblock contains a copy of the device item for that device. In a transaction which drops a chunk but doesn't create any new ones, we were correctly updating the device item in the chunk tree but not copying over the new bytes_used value to the superblock. This can be seen by doing the following: # dd if=/dev/zero of=test bs=4096 count=2621440 # mkfs.btrfs test # mount test /root/temp # cd /root/temp # for i in {00..10}; do dd if=/dev/zero of=$i bs=4096 count=32768; done # sync # rm * # sync # btrfs balance start -dusage=0 . # sync # cd # umount /root/temp # btrfs check test For btrfs-check to detect this, you will also need my patch at https://github.com/kdave/btrfs-progs/pull/991. Change btrfs_remove_dev_extents() so that it adds the devices to the fs_info->post_commit_list if they're not there already. This causes btrfs_commit_device_sizes() to be called, which updates the bytes_used value in the superblock. Fixes: bbbf7243d62d ("btrfs: combine device update operations during transaction commit") CC: stable@vger.kernel.org # 5.10+ Reviewed-by: Qu Wenruo Signed-off-by: Mark Harmstone Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/volumes.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 89835071cfea..f475b4b7c457 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -3282,6 +3282,12 @@ int btrfs_remove_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset) device->bytes_used - dev_extent_len); atomic64_add(dev_extent_len, &fs_info->free_chunk_space); btrfs_clear_space_info_full(fs_info); + + if (list_empty(&device->post_commit_list)) { + list_add_tail(&device->post_commit_list, + &trans->transaction->dev_update_list); + } + mutex_unlock(&fs_info->chunk_mutex); } } -- 2.50.1