fix ITER_PIPE interaction with direct_IO

by making sure we call iov_iter_advance() on original
iov_iter even if direct_IO (done on its copy) has returned 0.
It's a no-op for old iov_iter flavours and does the right thing
(== truncation of the stuff we'd allocated, but not filled) in
ITER_PIPE case.  Failures (e.g. -EIO) get caught and dealt with
by cleanup in generic_file_read_iter().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 5 insertions, 11 deletions

diff --git a/fs/splice.c b/fs/splice.c
index aa38901a4f10..153d4f3bd441 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -315,15 +315,9 @@ ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
                 *ppos = kiocb.ki_pos;
                 file_accessed(in);
         } else if (ret < 0) {
-                if (WARN_ON(to.idx != idx || to.iov_offset)) {
-                        /*
-                         * a bogus ->read_iter() has copied something and still
-                         * returned an error instead of a short read.
-                         */
-                        to.idx = idx;
-                        to.iov_offset = 0;
-                        iov_iter_advance(&to, 0); /* to free what was emitted */
-                }
+                to.idx = idx;
+                to.iov_offset = 0;
+                iov_iter_advance(&to, 0); /* to free what was emitted */
                 /*
                  * callers of ->splice_read() expect -EAGAIN on
                  * "can't put anything in there", rather than -EFAULT.
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 92f16cfb81e8..26cf153e3714 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -317,7 +317,7 @@ xfs_file_dio_aio_read(
         data = *to;
         ret = __blockdev_direct_IO(iocb, inode, target->bt_bdev, &data,
                         xfs_get_blocks_direct, NULL, NULL, 0);
-        if (ret > 0) {
+        if (ret >= 0) {
                 iocb->ki_pos += ret;
                 iov_iter_advance(to, ret);
         }
diff --git a/mm/filemap.c b/mm/filemap.c
index 8a287dfc5372..6b965efe215e 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1920,7 +1920,7 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
                         retval = mapping->a_ops->direct_IO(iocb, &data);
                 }
 
-                if (retval > 0) {
+                if (retval >= 0) {
                         iocb->ki_pos += retval;
                         iov_iter_advance(iter, retval);
                 }