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Date:   Sat, 17 Oct 2020 20:06:51 +0900
From:   "Dae R. Jeong" <dae.r.jeong@kaist.ac.kr>
To:     song@kernel.org
Cc:     yjkwon@kaist.ac.kr, linux-raid@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: WARNING in md_ioctl
Message-ID: <20201017110651.GA1602260@dragonet>
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Hi,

I looked into the warning "WARNING in md_ioctl" found by Syzkaller.
(https://syzkaller.appspot.com/bug?id=fbf9eaea2e65bfcabb4e2750c3ab0892867edea1)
I suspect that it is caused by a race between two concurrenct ioctl()s as belows.

CPU1 (md_ioctl())                          CPU2 (md_ioctl())
------                                     ------
set_bit(MD_CLOSING, &mddev->flags);
did_set_md_closing = true;
                                           WARN_ON_ONCE(test_bit(MD_CLOSING, &mddev->flags));

if(did_set_md_closing)
    clear_bit(MD_CLOSING, &mddev->flags);

If the above is correct, this warning is introduced
in the commit 065e519e("md: MD_CLOSING needs to be cleared after called md_set_readonly or do_md_stop").
Could you please take a look into this?

Best regards,
Dae R. Jeong