Comment 8 for bug 1217158

Same code in 5.6, so I assume it's potentially also affected:

...
    677 # ifndef UNIV_HOTBACKUP
    678 ut_a(block->page.buf_fix_count > 0);
    679 # endif /* !UNIV_HOTBACKUP */
    680 /* fall through */
    681 case BUF_BLOCK_READY_FOR_USE:
    682 case BUF_BLOCK_MEMORY:
    683 case BUF_BLOCK_REMOVE_HASH:
    684 goto ok;
    685 }
    686 ut_error;
    687 ok:
    688 return((buf_frame_t*) block->frame);
    689 }
"Percona-Server-5.6.12-rc60.4/storage/innobase/include/buf0buf.ic" line 689 of 1
424 --48%-- col 1