From d3914d6030aa6be2993dfc223d096ff93018c236 Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Fri, 9 May 2025 17:08:50 +0100 Subject: [PATCH] btrfs: fix invalid data space release when truncating block in NOCOW mode If when truncating a block we fail to reserve data space and then we proceed anyway because we can do a NOCOW write, if we later get an error when trying to get the folio from the inode's mapping, we end up releasing data space that we haven't reserved, screwing up the bytes_may_use counter from the data space_info, eventually resulting in an underflow when all other reservations done by other tasks are released, if any, or right away if there are no other reservations at the moment. This is because when we get an error when trying to grab the block's folio we call btrfs_delalloc_release_space(), which releases metadata (which we have reserved) and data (which we haven't reserved). Fix this by calling btrfs_delalloc_release_space() only if we did reserve data space, that is, if we aren't falling back to NOCOW, meaning the local variable @only_release_metadata has a false value, otherwise release only metadata by calling btrfs_delalloc_release_metadata(). Fixes: 6d4572a9d71d ("btrfs: allow btrfs_truncate_block() to fallback to nocow for data space reservation") Reviewed-by: Qu Wenruo Signed-off-by: Filipe Manana Signed-off-by: David Sterba --- fs/btrfs/inode.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 964088d3f3f7..b189371c142f 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -4931,8 +4931,11 @@ again: folio = __filemap_get_folio(mapping, index, FGP_LOCK | FGP_ACCESSED | FGP_CREAT, mask); if (IS_ERR(folio)) { - btrfs_delalloc_release_space(inode, data_reserved, block_start, - blocksize, true); + if (only_release_metadata) + btrfs_delalloc_release_metadata(inode, blocksize, true); + else + btrfs_delalloc_release_space(inode, data_reserved, + block_start, blocksize, true); btrfs_delalloc_release_extents(inode, blocksize); ret = -ENOMEM; goto out; -- 2.25.1