The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a60adce85f4bb5c1ef8ffcebadd702cafa2f3696 Mon Sep 17 00:00:00 2001

From: Josef Bacik josef@toxicpanda.com Date: Tue, 24 Sep 2019 16:50:44 -0400 Subject: [PATCH] btrfs: use btrfs_block_group_cache_done in update_block_group

When free'ing extents in a block group we check to see if the block group is not cached, and then cache it if we need to. However we'll just carry on as long as we're loading the cache. This is problematic because we are dirtying the block group here. If we are fast enough we could do a transaction commit and clear the free space cache while we're still loading the space cache in another thread. This truncates the free space inode, which will keep it from loading the space cache.

Fix this by using the btrfs_block_group_cache_done helper so that we try to load the space cache unconditionally here, which will result in the caller waiting for the fast caching to complete and keep us from truncating the free space inode.

CC: stable@vger.kernel.org # 4.4+ Signed-off-by: Josef Bacik josef@toxicpanda.com Reviewed-by: Nikolay Borisov nborisov@suse.com Signed-off-by: David Sterba dsterba@suse.com

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c index 384659dc7818..540a7a63601e 100644 --- a/fs/btrfs/block-group.c +++ b/fs/btrfs/block-group.c @@ -2661,7 +2661,7 @@ int btrfs_update_block_group(struct btrfs_trans_handle *trans, * is because we need the unpinning stage to actually add the * space back to the block group, otherwise we will leak space. */ - if (!alloc && cache->cached == BTRFS_CACHE_NO) + if (!alloc && !btrfs_block_group_cache_done(cache)) btrfs_cache_block_group(cache, 1);

byte_in_group = bytenr - cache->key.objectid;