dax: fix conversion of holes to PMDs

When we get a DAX PMD fault for a write it is possible that there could
be some number of 4k zero pages already present for the same range that
were inserted to service reads from a hole.  These 4k zero pages need to
be unmapped from the VMAs and removed from the struct address_space
radix tree before the real DAX PMD entry can be inserted.

For PTE faults this same use case also exists and is handled by a
combination of unmap_mapping_range() to unmap the VMAs and
delete_from_page_cache() to remove the page from the address_space radix
tree.

For PMD faults we do have a call to unmap_mapping_range() (protected by
a buffer_new() check), but nothing clears out the radix tree entry.  The
buffer_new() check is also incorrect as the current ext4 and XFS
filesystem code will never return a buffer_head with BH_New set, even
when allocating new blocks over a hole.  Instead the filesystem will
zero the blocks manually and return a buffer_head with only BH_Mapped
set.

Fix this situation by removing the buffer_new() check and adding a call
to truncate_inode_pages_range() to clear out the radix tree entries
before we insert the DAX PMD.

Signed-off-by: Ross Zwisler <[email protected]>
Reported-by: Dan Williams <[email protected]>
Tested-by: Dan Williams <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: "J. Bruce Fields" <[email protected]>
Cc: "Theodore Ts'o" <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Andreas Dilger <[email protected]>
Cc: Dave Chinner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jeff Layton <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Dave Hansen <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 10 insertions, 10 deletions

diff --git a/fs/dax.c b/fs/dax.c
index 513bba5f1e02..5b84a46201c2 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -589,6 +589,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 	bool write = flags & FAULT_FLAG_WRITE;
 	struct block_device *bdev;
 	pgoff_t size, pgoff;
+	loff_t lstart, lend;
 	sector_t block;
 	int result = 0;
 
@@ -643,15 +644,13 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 		goto fallback;
 	}
 
-	/*
-	 * If we allocated new storage, make sure no process has any
-	 * zero pages covering this hole
-	 */
-	if (buffer_new(&bh)) {
-		i_mmap_unlock_read(mapping);
-		unmap_mapping_range(mapping, pgoff << PAGE_SHIFT, PMD_SIZE, 0);
-		i_mmap_lock_read(mapping);
-	}
+	/* make sure no process has any zero pages covering this hole */
+	lstart = pgoff << PAGE_SHIFT;
+	lend = lstart + PMD_SIZE - 1; /* inclusive */
+	i_mmap_unlock_read(mapping);
+	unmap_mapping_range(mapping, lstart, PMD_SIZE, 0);
+	truncate_inode_pages_range(mapping, lstart, lend);
+	i_mmap_lock_read(mapping);
 
 	/*
 	 * If a truncate happened while we were allocating blocks, we may
@@ -665,7 +664,8 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 		goto out;
 	}
 	if ((pgoff | PG_PMD_COLOUR) >= size) {
-		dax_pmd_dbg(&bh, address, "pgoff unaligned");
+		dax_pmd_dbg(&bh, address,
+				"offset + huge page size > file size");
 		goto fallback;
 	}