btrfs: warn when extent buffer leak test fails

Although we have btrfs_extent_buffer_leak_debug_check() (enabled by
CONFIG_BTRFS_DEBUG option) to detect and warn QA testers that we have
some extent buffer leakage, it's just pr_err(), not noisy enough for
fstests to cache.

So here we trigger a WARN_ON() if the allocated_ebs list is not empty.
Reviewed-by: NFilipe Manana <fdmanana@suse.com>
Signed-off-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -75,6 +75,7 @@ void btrfs_extent_buffer_leak_debug_check(struct btrfs_fs_info *fs_info)
 	if (!fs_info->allocated_ebs.next)
 		return;
 
+	WARN_ON(!list_empty(&fs_info->allocated_ebs));
 	spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
 	while (!list_empty(&fs_info->allocated_ebs)) {
 		eb = list_first_entry(&fs_info->allocated_ebs,