Commit 8346c416 authored Oct 01, 2015 by Ross Zwisler Committed by Linus Torvalds Oct 01, 2015

dax: fix NULL pointer in __dax_pmd_fault()



Commit 46c043ed ("mm: take i_mmap_lock in unmap_mapping_range() for
DAX") moved some code in __dax_pmd_fault() that was responsible for
zeroing newly allocated PMD pages.  The new location didn't properly set
up 'kaddr', so when run this code resulted in a NULL pointer BUG.

Fix this by getting the correct 'kaddr' via bdev_direct_access().

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reported-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Matthew Wilcox <willy@linux.intel.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 2f84a899

fs/dax.c

+12 −1

Original line number	Diff line number	Diff line
		@@ -569,8 +569,20 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
		if (!buffer_size_valid(&bh) \|\| bh.b_size < PMD_SIZE)
		goto fallback;

		sector = bh.b_blocknr << (blkbits - 9);

		if (buffer_unwritten(&bh) \|\| buffer_new(&bh)) {
		int i;

		length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn,
		bh.b_size);
		if (length < 0) {
		result = VM_FAULT_SIGBUS;
		goto out;
		}
		if ((length < PMD_SIZE) \|\| (pfn & PG_PMD_COLOUR))
		goto fallback;

		for (i = 0; i < PTRS_PER_PMD; i++)
		clear_pmem(kaddr + i * PAGE_SIZE, PAGE_SIZE);
		wmb_pmem();
		@@ -623,7 +635,6 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
		result = VM_FAULT_NOPAGE;
		spin_unlock(ptl);
		} else {
		sector = bh.b_blocknr << (blkbits - 9);
		length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn,
		bh.b_size);
		if (length < 0) {

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