6.15-stable review patch. If anyone has any objections, please let me know.
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From: Filipe Manana fdmanana@suse.com
[ Upstream commit d3914d6030aa6be2993dfc223d096ff93018c236 ]
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 wqu@suse.com Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 90f5da3c520ac..8a3f44302788c 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -4849,8 +4849,11 @@ int btrfs_truncate_block(struct btrfs_inode *inode, loff_t from, loff_t len, 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;