On Mon, Oct 19, 2020 at 12:03 AM Dae R. Jeong [off-list ref] wrote:

quoted

diff --git i/drivers/md/md.c w/drivers/md/md.c
index 6072782070230..49442a3f4605b 100644
--- i/drivers/md/md.c
+++ w/drivers/md/md.c

@@ -7591,8 +7591,10 @@ static int md_ioctl(struct block_device *bdev,

fmode_t mode,
                        err = -EBUSY;
                        goto out;
                }
-               WARN_ON_ONCE(test_bit(MD_CLOSING, &mddev->flags));
-               set_bit(MD_CLOSING, &mddev->flags);
+               if (test_and_set_bit(MD_CLOSING, &mddev->flags)) {
+                       err = -EBUSY;
+                       goto out;
+               }
                did_set_md_closing = true;
                mutex_unlock(&mddev->open_mutex);
                sync_blockdev(bdev);

Could you please test whether this fixes the issue?

Since &mddev->open_mutex is held when testing a bit of mddev->flags, I
modified the code just a little bit by putting mutex_unlock() as
belows.

Good catch! The fix looks good. Would you like to submit a patch for it?

Thanks,
Song