[PATCH 4.2 051/258] dax: fix O_DIRECT I/O to the last block of a blockdev

[Greg Kroah-Hartman]

4.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jeff Moyer <jmoyer@xxxxxxxxxx>

commit e94f5a2285fc94202a9efb2c687481f29b64132c upstream.

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.

Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
Tested-by:  Linda Knippers <linda.knippers@xxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/dax.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/dax.c
+++ b/fs/dax.c
@@ -116,7 +116,8 @@ static ssize_t dax_io(struct inode *inod
 		unsigned 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;
 


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