linux-kernel - Re: [PATCH] md: fix a warning caused by a race between concurrent md

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Date:   Thu, 5 Nov 2020 19:13:59 -0800
From:   Song Liu <song@...nel.org>
To:     "Dae R. Jeong" <dae.r.jeong@...st.ac.kr>
Cc:     linux-raid <linux-raid@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>, yjkwon@...st.ac.kr
Subject: Re: [PATCH] md: fix a warning caused by a race between concurrent md_ioctl()s

On Wed, Oct 21, 2020 at 6:21 PM Dae R. Jeong <dae.r.jeong@...st.ac.kr> wrote:
>
> Syzkaller reports a warning as belows.
> WARNING: CPU: 0 PID: 9647 at drivers/md/md.c:7169
> ...
> Call Trace:
> ...
> RIP: 0010:md_ioctl+0x4017/0x5980 drivers/md/md.c:7169
> RSP: 0018:ffff888096027950 EFLAGS: 00010293
> RAX: ffff88809322c380 RBX: 0000000000000932 RCX: ffffffff84e266f2
> RDX: 0000000000000000 RSI: ffffffff84e299f7 RDI: 0000000000000007
> RBP: ffff888096027bc0 R08: ffff88809322c380 R09: ffffed101341a482
> R10: ffff888096027940 R11: ffff88809a0d240f R12: 0000000000000932
> R13: ffff8880a2c14100 R14: ffff88809a0d2268 R15: ffff88809a0d2408
>  __blkdev_driver_ioctl block/ioctl.c:304 [inline]
>  blkdev_ioctl+0xece/0x1c10 block/ioctl.c:606
>  block_ioctl+0xee/0x130 fs/block_dev.c:1930
>  vfs_ioctl fs/ioctl.c:46 [inline]
>  file_ioctl fs/ioctl.c:509 [inline]
>  do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:696
>  ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
>  __do_sys_ioctl fs/ioctl.c:720 [inline]
>  __se_sys_ioctl fs/ioctl.c:718 [inline]
>  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
>  do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> This is caused by a race between two concurrenct md_ioctl()s closing
> the array.
> 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);
>
> Fix the warning by returning immediately if the MD_CLOSING bit is set
> in &mddev->flags which indicates that the array is being closed.
>
> Fixes: 065e519e71b2 ("md: MD_CLOSING needs to be cleared after called md_set_readonly or do_md_stop")
> Reported-by: syzbot+1e46a0864c1a6e9bd3d8@...kaller.appspotmail.com
> Signed-off-by: Dae R. Jeong <dae.r.jeong@...st.ac.kr>

Applied to md-next. Thanks!


> ---
>  drivers/md/md.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> 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);
> --
> 2.25.1
>
>
>