md: set mddev readonly flag on blkdev BLKROSET ioctl

When the user sets the block device to readwrite then the mddev should
follow suit.  Otherwise, the BUG_ON in md_write_start() will be set to
trigger.

The reverse direction, setting mddev->ro to match a set readonly
request, can be ignored because the blkdev level readonly flag precludes
the need to have mddev->ro set correctly.  Nevermind the fact that
setting mddev->ro to 1 may fail if the array is in use.

Cc: <stable@kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 29 insertions, 0 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index a20a71e5efd3..08f665178c3b 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5489,6 +5489,7 @@ static int md_ioctl(struct block_device *bdev, fmode_t mode,
         int err = 0;
         void __user *argp = (void __user *)arg;
         mddev_t *mddev = NULL;
+        int ro;
 
         if (!capable(CAP_SYS_ADMIN))
                 return -EACCES;
@@ -5624,6 +5625,34 @@ static int md_ioctl(struct block_device *bdev, fmode_t mode,
                         err = do_md_stop(mddev, 1, 1);
                         goto done_unlock;
 
+                case BLKROSET:
+                        if (get_user(ro, (int __user *)(arg))) {
+                                err = -EFAULT;
+                                goto done_unlock;
+                        }
+                        err = -EINVAL;
+
+                        /* if the bdev is going readonly the value of mddev->ro
+                         * does not matter, no writes are coming
+                         */
+                        if (ro)
+                                goto done_unlock;
+
+                        /* are we are already prepared for writes? */
+                        if (mddev->ro != 1)
+                                goto done_unlock;
+
+                        /* transitioning to readauto need only happen for
+                         * arrays that call md_write_start
+                         */
+                        if (mddev->pers) {
+                                err = restart_array(mddev);
+                                if (err == 0) {
+                                        mddev->ro = 2;
+                                        set_disk_ro(mddev->gendisk, 0);
+                                }
+                        }
+                        goto done_unlock;
         }
 
         /*