dax: fix __dax_pmd_fault crash
authorDan Williams <dan.j.williams@intel.com>
Fri, 13 Nov 2015 02:33:54 +0000 (18:33 -0800)
committerDan Williams <dan.j.williams@intel.com>
Fri, 13 Nov 2015 02:33:54 +0000 (18:33 -0800)
commit152d7bd80dca5ce77ec2d7313149a2ab990e808e
tree0278dcde82a608216233147c2adf58fa0911b7b0
parent8de5dff8bae634497f4413bc3067389f2ed267da
dax: fix __dax_pmd_fault crash

Since 4.3 introduced devm_memremap_pages() the pfns handled by DAX may
optionally have a struct page backing.  When a mapped pfn reaches
vmf_insert_pfn_pmd() it fails with a crash signature like the following:

 kernel BUG at mm/huge_memory.c:905!
 [..]
 Call Trace:
  [<ffffffff812a73ba>] __dax_pmd_fault+0x2ea/0x5b0
  [<ffffffffa01a4182>] xfs_filemap_pmd_fault+0x92/0x150 [xfs]
  [<ffffffff811fbe02>] handle_mm_fault+0x312/0x1b50

Fix this by falling back to 4K mappings in the pfn_valid() case.  Longer
term, vmf_insert_pfn_pmd() needs to grow support for architectures that
can provide a 'pmd_special' capability.

Cc: <stable@vger.kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
fs/dax.c