iomap_dio_actor(): fix iov_iter bugs

1) Ignoring return value from iov_iter_zero() is wrong
for iovec-backed case as well as for pipes - it can fail.

2) Failure to fault destination pages in 25Mb into a 50Mb iovec
should not act as if nothing in the area had been read, nevermind
that the first 25Mb might have *already* been read by that point.

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

1 files changed, 15 insertions, 9 deletions

diff --git a/fs/iomap.c b/fs/iomap.c
index be61cf742b5e..9c41008833ac 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -848,6 +848,7 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
         struct bio *bio;
         bool need_zeroout = false;
         int nr_pages, ret;
+        size_t copied = 0;
 
         if ((pos | length | align) & ((1 << blkbits) - 1))
                 return -EINVAL;
@@ -859,7 +860,7 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
                 /*FALLTHRU*/
         case IOMAP_UNWRITTEN:
                 if (!(dio->flags & IOMAP_DIO_WRITE)) {
-                        iov_iter_zero(length, dio->submit.iter);
+                        length = iov_iter_zero(length, dio->submit.iter);
                         dio->size += length;
                         return length;
                 }
@@ -896,8 +897,11 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
         }
 
         do {
-                if (dio->error)
+                size_t n;
+                if (dio->error) {
+                        iov_iter_revert(dio->submit.iter, copied);
                         return 0;
+                }
 
                 bio = bio_alloc(GFP_KERNEL, nr_pages);
                 bio_set_dev(bio, iomap->bdev);
@@ -910,20 +914,24 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
                 ret = bio_iov_iter_get_pages(bio, &iter);
                 if (unlikely(ret)) {
                         bio_put(bio);
-                        return ret;
+                        return copied ? copied : ret;
                 }
 
+                n = bio->bi_iter.bi_size;
                 if (dio->flags & IOMAP_DIO_WRITE) {
                         bio_set_op_attrs(bio, REQ_OP_WRITE, REQ_SYNC | REQ_IDLE);
-                        task_io_account_write(bio->bi_iter.bi_size);
+                        task_io_account_write(n);
                 } else {
                         bio_set_op_attrs(bio, REQ_OP_READ, 0);
                         if (dio->flags & IOMAP_DIO_DIRTY)
                                 bio_set_pages_dirty(bio);
                 }
 
-                dio->size += bio->bi_iter.bi_size;
-                pos += bio->bi_iter.bi_size;
+                iov_iter_advance(dio->submit.iter, n);
+
+                dio->size += n;
+                pos += n;
+                copied += n;
 
                 nr_pages = iov_iter_npages(&iter, BIO_MAX_PAGES);
 
@@ -939,9 +947,7 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
                 if (pad)
                         iomap_dio_zero(dio, iomap, pos, fs_block_size - pad);
         }
-
-        iov_iter_advance(dio->submit.iter, length);
-        return length;
+        return copied;
 }
 
 ssize_t