Re: [PATCH] md: adding a new flag MD_DELETING

[Zhong Lidong <lidong.zhong@suse.com>]

Hi Song,

Could you share your opinion about this patch please?

Thanks,
Lidong

On 4/28/21 4:29 PM, Lidong Zhong wrote:
> The mddev data structure is freed in mddev_delayed_delete(), which is
> schedualed after the array is deconfigured completely when stopping. So
> there is a race window between md_open() and do_md_stop(), which leads
> to /dev/mdX can still be opened by userspace even it's not accessible
> any more. As a result, a DeviceDisappeared event will not be able to be
> monitored by mdadm in monitor mode. This patch tries to fix it by adding
> this new flag MD_DELETING.
> 
> Signed-off-by: Lidong Zhong <lidong.zhong@suse.com>
> ---
>  drivers/md/md.c | 4 +++-
>  drivers/md/md.h | 2 ++
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 21da0c48f6c2..566df2491318 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -6439,6 +6439,7 @@ static int do_md_stop(struct mddev *mddev, int mode,
>  		md_clean(mddev);
>  		if (mddev->hold_active == UNTIL_STOP)
>  			mddev->hold_active = 0;
> +		set_bit(MD_DELETING, &mddev->flags);
>  	}
>  	md_new_event(mddev);
>  	sysfs_notify_dirent_safe(mddev->sysfs_state);
> @@ -7829,7 +7830,8 @@ static int md_open(struct block_device *bdev, fmode_t mode)
>  	if ((err = mutex_lock_interruptible(&mddev->open_mutex)))
>  		goto out;
>  
> -	if (test_bit(MD_CLOSING, &mddev->flags)) {
> +	if (test_bit(MD_CLOSING, &mddev->flags) ||
> +            (test_bit(MD_DELETING, &mddev->flags) && mddev->pers == NULL)) {
>  		mutex_unlock(&mddev->open_mutex);
>  		err = -ENODEV;
>  		goto out;
> diff --git a/drivers/md/md.h b/drivers/md/md.h
> index bcbba1b5ec4a..83c7aa61699f 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -262,6 +262,8 @@ enum mddev_flags {
>  	MD_BROKEN,              /* This is used in RAID-0/LINEAR only, to stop
>  				 * I/O in case an array member is gone/failed.
>  				 */
> +	MD_DELETING,		/* If set, we are deleting the array, do not open
> +				 * it then */
>  };
>  
>  enum mddev_sb_flags {
>