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Date:   Mon, 19 Oct 2020 16:03:19 +0900
From:   "Dae R. Jeong" <dae.r.jeong@kaist.ac.kr>
To:     Song Liu <song@kernel.org>
Cc:     yjkwon@kaist.ac.kr, linux-raid <linux-raid@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: WARNING in md_ioctl
Message-ID: <20201019070319.GA1811280@dragonet>
References: <20201017110651.GA1602260@dragonet>
 <CAPhsuW583=org7AOR-W2vcQV3pTBxin2LG1tb3On=x6VtjXvxQ@mail.gmail.com>
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> 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.

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 98bac4f304ae..643f7f5be49b 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -7590,8 +7590,11 @@ 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)) {
+			mutex_unlock(&mddev->open_mutex);
+			err = -EBUSY;
+			goto out;
+		}
 		did_set_md_closing = true;
 		mutex_unlock(&mddev->open_mutex);
 		sync_blockdev(bdev);

The warning no longer recurs (of course, we removed
WARN_ON_ONCE()). As I am not familiar with this code, I do not see any
other problem.

Best regards,
Dae R. Jeong