linux-kernel - Re: [Nbd] [RFC PATCH 1/1] nbd: replace kill_bdev() with __invalidate

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Date:   Wed, 22 Mar 2017 13:48:03 -0700
From:   Ming Lin <mlin@...nel.org>
To:     Josef Bacik <jbacik@...com>
Cc:     nbd-general@...ts.sourceforge.net,
        Ratna Manoj Bolla <manoj.br@...il.com>,
        lkml <linux-kernel@...r.kernel.org>, linux-block@...r.kernel.org,
        jianshu.ljs@...baba-inc.com,
        "LIU, Fei" <james.liu@...baba-inc.com>,
        Markus Pargmann <mpa@...gutronix.de>,
        xiongwei.jiang@...baba-inc.com
Subject: Re: [Nbd] [RFC PATCH 1/1] nbd: replace kill_bdev() with __invalidate_device()

On Mon, Mar 20, 2017 at 3:58 PM, Ming Lin <mlin@...nel.org> wrote:
> From: Ratna Manoj Bolla <manoj.br@...il.com>
>
> When a filesystem is mounted on a nbd device and on a disconnect, because
> of kill_bdev(), and resetting bdev size to zero, buffer_head mappings are
> getting destroyed under mounted filesystem.
>
> After a bdev size reset(i.e bdev->bd_inode->i_size = 0) on a disconnect,
> followed by a sys_umount(),
>         generic_shutdown_super()->...
>         ->__sync_blockdev()->...
>         -blkdev_writepages()->...
>         ->do_invalidatepage()->...
>         -discard_buffer()   is discarding superblock buffer_head assumed
> to be in mapped state by ext4_commit_super().
>
> [mlin: ported to 4.11-rc2]
> Signed-off-by: Ratna Manoj Bolla <manoj.br@...il.com
> ---
>  drivers/block/nbd.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index cb4ccfc..a6a3643 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -125,7 +125,8 @@ static const char *nbdcmd_to_ascii(int cmd)
>
>  static int nbd_size_clear(struct nbd_device *nbd, struct block_device *bdev)
>  {
> -       bd_set_size(bdev, 0);
> +       if (bdev->bd_openers <= 1)
> +               bd_set_size(bdev, 0);
>         set_capacity(nbd->disk, 0);
>         kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
>
> @@ -603,6 +604,8 @@ static void nbd_reset(struct nbd_device *nbd)
>
>  static void nbd_bdev_reset(struct block_device *bdev)
>  {
> +       if (bdev->bd_openers > 1)
> +               return;
>         set_device_ro(bdev, false);
>         bdev->bd_inode->i_size = 0;
>         if (max_part > 0) {
> @@ -666,7 +669,8 @@ static int nbd_clear_sock(struct nbd_device *nbd, struct block_device *bdev)
>  {
>         sock_shutdown(nbd);
>         nbd_clear_que(nbd);
> -       kill_bdev(bdev);
> +
> +       __invalidate_device(bdev, true);
>         nbd_bdev_reset(bdev);
>         /*
>          * We want to give the run thread a chance to wait for everybody
> --
> 1.8.3.1

Hi Josef,

Any comments?

Thanks,
Ming