diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 3ec494f5d7ee73c35ccf3cfbb8fd048d4432d8fc..d5246e277f179fd8b309ba515b1d135f1006411d 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -771,10 +771,6 @@ iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 		 * Otherwise there's a nasty deadlock on copying from the
 		 * same page as we're writing to, without it being marked
 		 * up-to-date.
-		 *
-		 * Not only is this an optimisation, but it is also required
-		 * to check that the address is actually valid, when atomic
-		 * usercopies are used, below.
 		 */
 		if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
 			status = -EFAULT;
@@ -791,25 +787,24 @@ iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 
 		copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
 
-		copied = iomap_write_end(inode, pos, bytes, copied, page, iomap,
+		status = iomap_write_end(inode, pos, bytes, copied, page, iomap,
 				srcmap);
 
 		cond_resched();
 
-		iov_iter_advance(i, copied);
-		if (unlikely(copied == 0)) {
+		if (unlikely(status == 0)) {
 			/*
-			 * If we were unable to copy any data at all, we must
-			 * fall back to a single segment length write.
-			 *
-			 * If we didn't fallback here, we could livelock
-			 * because not all segments in the iov can be copied at
-			 * once without a pagefault.
+			 * A short copy made iomap_write_end() reject the
+			 * thing entirely.  Might be memory poisoning
+			 * halfway through, might be a race with munmap,
+			 * might be severe memory pressure.
 			 */
-			bytes = min_t(unsigned long, PAGE_SIZE - offset,
-						iov_iter_single_seg_count(i));
+			if (copied)
+				bytes = copied;
 			goto again;
 		}
+		copied = status;
+		iov_iter_advance(i, copied);
 		pos += copied;
 		written += copied;
 		length -= copied;
diff --git a/mm/filemap.c b/mm/filemap.c
index edb94663c5df0da41492f6a0f7061d3b8bdd4bfa..a00fc493f5cf1fc1c52126325bb708658494db83 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3518,10 +3518,6 @@ ssize_t generic_perform_write(struct file *file,
 		 * Otherwise there's a nasty deadlock on copying from the
 		 * same page as we're writing to, without it being marked
 		 * up-to-date.
-		 *
-		 * Not only is this an optimisation, but it is also required
-		 * to check that the address is actually valid, when atomic
-		 * usercopies are used, below.
 		 */
 		if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
 			status = -EFAULT;
@@ -3548,24 +3544,22 @@ ssize_t generic_perform_write(struct file *file,
 						page, fsdata);
 		if (unlikely(status < 0))
 			break;
-		copied = status;
 
 		cond_resched();
 
-		iov_iter_advance(i, copied);
-		if (unlikely(copied == 0)) {
+		if (unlikely(status == 0)) {
 			/*
-			 * If we were unable to copy any data at all, we must
-			 * fall back to a single segment length write.
-			 *
-			 * If we didn't fallback here, we could livelock
-			 * because not all segments in the iov can be copied at
-			 * once without a pagefault.
+			 * A short copy made ->write_end() reject the
+			 * thing entirely.  Might be memory poisoning
+			 * halfway through, might be a race with munmap,
+			 * might be severe memory pressure.
 			 */
-			bytes = min_t(unsigned long, PAGE_SIZE - offset,
-						iov_iter_single_seg_count(i));
+			if (copied)
+				bytes = copied;
 			goto again;
 		}
+		copied = status;
+		iov_iter_advance(i, copied);
 		pos += copied;
 		written += copied;