md: raid10: remove VLAIS

The raid10 driver can't be built with clang since it uses a variable
length array in a structure (VLAIS):

drivers/md/raid10.c:4583:17: error: fields must have a constant size:
  'variable length array in structure' extension will never be supported

Allocate the r10bio struct with kmalloc instead of using the VLAIS
construct.

Shaohua: set the MD_RECOVERY_INTR bit
Neil Brown: use GFP_NOIO
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/raid10.c

@@ -4578,15 +4578,18 @@ static int handle_reshape_read_error(struct mddev *mddev,
 	/* Use sync reads to get the blocks from somewhere else */
 	int sectors = r10_bio->sectors;
 	struct r10conf *conf = mddev->private;
-	struct {
-		struct r10bio r10_bio;
-		struct r10dev devs[conf->copies];
-	} on_stack;
-	struct r10bio *r10b = &on_stack.r10_bio;
+	struct r10bio *r10b;
 	int slot = 0;
 	int idx = 0;
 	struct page **pages;
 
+	r10b = kmalloc(sizeof(*r10b) +
+	       sizeof(struct r10dev) * conf->copies, GFP_NOIO);
+	if (!r10b) {
+		set_bit(MD_RECOVERY_INTR, &mddev->recovery);
+		return -ENOMEM;
+	}
+
 	/* reshape IOs share pages from .devs[0].bio */
 	pages = get_resync_pages(r10_bio->devs[0].bio)->pages;
 
@@ -4635,11 +4638,13 @@ static int handle_reshape_read_error(struct mddev *mddev,
 			/* couldn't read this block, must give up */
 			set_bit(MD_RECOVERY_INTR,
 				&mddev->recovery);
+			kfree(r10b);
 			return -EIO;
 		}
 		sectors -= s;
 		idx++;
 	}
+	kfree(r10b);
 	return 0;
 }