btrfs: prevent __btrfs_dump_space_info() to underflow its free space

It's not uncommon where __btrfs_dump_space_info() gets called
under over-commit situations.

In that case free space would underflow as total allocated space is not
enough to handle all the over-committed space.

Such underflow values can sometimes cause confusion for users enabled
enospc_debug mount option, and takes some seconds for developers to
convert the underflow value to signed result.

Just output the free space as s64 to avoid such problem.

Reported-by: Eli V <eliventer@gmail.com>
Link: https://lore.kernel.org/linux-btrfs/CAJtFHUSy4zgyhf-4d9T+KdJp9w=UgzC2A0V=VtmaeEpcGgm1-Q@mail.gmail.com/
CC: stable@vger.kernel.org # 5.4+
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index 5ada02e0e629fe8b43437b6296b27a8ffa167b7f..aa5be0b24987ad4366854d6d4ad59c2d096321a0 100644 (file)
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -414,9 +414,10 @@ static void __btrfs_dump_space_info(struct btrfs_fs_info *fs_info,
 {
        lockdep_assert_held(&info->lock);
 
-       btrfs_info(fs_info, "space_info %llu has %llu free, is %sfull",
+       /* The free space could be negative in case of overcommit */
+       btrfs_info(fs_info, "space_info %llu has %lld free, is %sfull",
                   info->flags,
-                  info->total_bytes - btrfs_space_info_used(info, true),
+                  (s64)(info->total_bytes - btrfs_space_info_used(info, true)),
                   info->full ? "" : "not ");
        btrfs_info(fs_info,
                "space_info total=%llu, used=%llu, pinned=%llu, reserved=%llu, may_use=%llu, readonly=%llu zone_unusable=%llu",