Commit 152d7bd8 authored Nov 12, 2015 by Dan Williams

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>

parent 8de5dff8

fs/dax.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -627,6 +627,13 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
		if ((length < PMD_SIZE) \|\| (pfn & PG_PMD_COLOUR))
		goto fallback;

		/*
		* TODO: teach vmf_insert_pfn_pmd() to support
		* 'pte_special' for pmds
		*/
		if (pfn_valid(pfn))
		goto fallback;

		if (buffer_unwritten(&bh) \|\| buffer_new(&bh)) {
		int i;
		for (i = 0; i < PTRS_PER_PMD; i++)

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