This has gotten Reviewed-by tags from Christoph and Ming Lei.
Al, are you the right person to merge this? Or is the correct person Jens,
whom I accidentally didn't include when I sent this out?
Just wanted to make sure this got merged, and to see whether it was targeting
v4.16 or v4.17.
On Mon, Feb 12, 2018 at 04:05:58PM -0700, Ross Zwisler wrote:
The following commit:
commit aa4d86163e4e ("block: loop: switch to VFS ITER_BVEC")
replaced __do_lo_send_write(), which used ITER_KVEC iterators, with
lo_write_bvec() which uses ITER_BVEC iterators. In this change, though,
the WRITE flag was lost:
- iov_iter_kvec(&from, ITER_KVEC | WRITE, &kvec, 1, len);
+ iov_iter_bvec(&i, ITER_BVEC, bvec, 1, bvec->bv_len);
This flag is necessary for the DAX case because we make decisions based on
whether or not the iterator is a READ or a WRITE in dax_iomap_actor() and
We end up going through this path in configurations where we combine a PMEM
device with 4k sectors, a loopback device and DAX. The consequence of this
missed flag is that what we intend as a write actually turns into a read in
the DAX code, so no data is ever written.
The very simplest test case is to create a loopback device and try and
write a small string to it, then hexdump a few bytes of the device to see
if the write took. Without this patch you read back all zeros, with this
you read back the string you wrote.
For XFS this causes us to fail or panic during the following xfstests:
xfs/074 xfs/078 xfs/216 xfs/217 xfs/250
For ext4 we have a similar issue where writes never happen, but we don't
currently have any xfstests that use loopback and show this issue.
Fix this by restoring the WRITE flag argument to iov_iter_bvec(). This
causes the xfstests to all pass.
Signed-off-by: Ross Zwisler <ross.zwisler(a)linux.intel.com>
Fixes: commit aa4d86163e4e ("block: loop: switch to VFS ITER_BVEC")
Cc: Christoph Hellwig <hch(a)lst.de>
Cc: Al Viro <viro(a)zeniv.linux.org.uk>
drivers/block/loop.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index d5fe720cf149..89d2ee00cced 100644
@@ -266,7 +266,7 @@ static int lo_write_bvec(struct file *file, struct bio_vec *bvec,
struct iov_iter i;
- iov_iter_bvec(&i, ITER_BVEC, bvec, 1, bvec->bv_len);
+ iov_iter_bvec(&i, ITER_BVEC | WRITE, bvec, 1, bvec->bv_len);
bw = vfs_iter_write(file, &i, ppos, 0);