dax: fix O_DIRECT I/O to the last block of a blockdev

commit bbab37ddc20b (block: Add support for DAX reads/writes to
block devices) caused a regression in mkfs.xfs.  That utility
sets the block size of the device to the logical block size
using the BLKBSZSET ioctl, and then issues a single sector read
from the last sector of the device.  This results in the dax_io
code trying to do a page-sized read from 512 bytes from the end
of the device.  The result is -ERANGE being returned to userspace.

The fix is to align the block to the page size before calling
get_block.

Thanks to willy for simplifying my original patch.

Cc: <stable@vger.kernel.org>
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Tested-by:  Linda Knippers <linda.knippers@hp.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/fs/dax.c b/fs/dax.c
index 93bf2f990ace462b31dba2ee239084e112b1dfd0..7ae6df7ea1d2d04962ef4554a6a2fa1efb977006 100644 (file)
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -119,7 +119,8 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
                size_t len;
                if (pos == max) {
                        unsigned blkbits = inode->i_blkbits;
-                       sector_t block = pos >> blkbits;
+                       long page = pos >> PAGE_SHIFT;
+                       sector_t block = page << (PAGE_SHIFT - blkbits);
                        unsigned first = pos - (block << blkbits);
                        long size;