[PATCH 1/3] Revert "dax: fix NULL pointer in __dax_pmd_fault()"

[Ross Zwisler <ross.zwisler@linux.intel.com>]

This reverts commit 8346c416d17bf5b4ea1508662959bb62e73fd6a5.

This commit did fix the issue it intended to fix, but it turns out that
the locking changes introduced by these two commits:

commit 843172978bb9 ("dax: fix race between simultaneous faults")
commit 46c043ede471 ("mm: take i_mmap_lock in unmap_mapping_range() for DAX")

had other issues as well, so they need to just be reverted.

The list of issues in DAX after these commits (some newly introduced by
the commits, some preexisting) can be found here:

https://lkml.org/lkml/2015/9/25/602

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/dax.c | 13 +------------
 1 file changed, 1 insertion(+), 12 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index bcfb14b..7ae6df7 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -569,20 +569,8 @@ 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();
@@ -635,6 +623,7 @@ 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) {
-- 
2.1.0