mm: improve dump_page() for compound pages

There was no protection against a corrupted struct page having an
implausible compound_head().  Sanity check that a compound page has a head
within reach of the maximum allocatable page (this will need to be
adjusted if one of the plans to allocate 1GB pages comes to fruition).  In
addition,

 - Print the mapping pointer using %p insted of %px.  The actual value of
   the pointer can be read out of the raw page dump and using %p gives a
   chance to correlate it with an earlier printk of the mapping pointer
 - Print the mapping pointer from the head page, not the tail page
   (the tail ->mapping pointer may be in use for other purposes, eg part
   of a list_head)
 - Print the order of the page for compound pages
 - Dump the raw head page as well as the raw page
 - Print the refcount from the head page, not the tail page

Suggested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Co-developed-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Link: http://lkml.kernel.org/r/20200211001536.1027652-12-jhubbard@nvidia.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>