linux-kernel - Re: [PATCH v2 3/3] md: sync blockdev before stopping raid or setting readonly

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Date: Thu, 18 Jan 2024 09:02:05 +0100
From: Mariusz Tkaczyk <mariusz.tkaczyk@...ux.intel.com>
To: linan666@...weicloud.com
Cc: song@...nel.org, shli@...com, neilb@...e.com, zlliu@...e.com,
 linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
 yukuai3@...wei.com, yi.zhang@...wei.com, houtao1@...wei.com,
 yangerkun@...wei.com
Subject: Re: [PATCH v2 3/3] md: sync blockdev before stopping raid or
 setting readonly

On Wed, 17 Jan 2024 17:37:07 +0800
linan666@...weicloud.com wrote:

> From: Li Nan <linan122@...wei.com>
> 
> Commit a05b7ea03d72 ("md: avoid crash when stopping md array races
> with closing other open fds.") added sync_block before stopping raid and
> setting readonly. Later in commit 260fa034ef7a ("md: avoid deadlock when
> dirty buffers during md_stop.") it is moved to ioctl. array_state_store()
> was ignored. Add sync blockdev to array_state_store() now.
> 
> Signed-off-by: Li Nan <linan122@...wei.com>
> ---
>  drivers/md/md.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 2c793992a604..aea39598457c 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -4477,6 +4477,7 @@ array_state_store(struct mddev *mddev, const char *buf,
> size_t len) {
>  	int err = 0;
>  	enum array_state st = match_word(buf, array_states);
> +	bool clear_md_closing = false;
>  
>  	/* No lock dependent actions */
>  	switch (st) {
> @@ -4511,6 +4512,16 @@ array_state_store(struct mddev *mddev, const char
> *buf, size_t len) spin_unlock(&mddev->lock);
>  		return err ?: len;
>  	}
> +
> +	/* we will call set readonly or stop raid, sync blockdev */
> +	if (st == clear || (mddev->pers && (st == readonly ||
> +	    st == inactive || (st == read_auto && md_is_rdwr(mddev))))) {
> +		err = mddev_sync_blockdev(mddev);
> +		if (err)
> +			return err;
> +		clear_md_closing = true;
> +	}
> +

Please reorganize it a little for readability:
I think if no mddev->pers we don't need to consider sync_blockdev at all. If
personality is there we can probably check for read-write. If it is not
read-write then nothing to sync. What about that:

if (mddev->pers && md_is_rdwr(mddev) &&
    (st == clear || st == readonly || st == inactive || st == read_auto)) 

Please note that I didn't test it so please let me know if you see issue in
proposed logic.
I think that we may be able to include it in "/* No lock dependent actions */"
switch. Please consider it too:

case clear:
case readonly:
case inactive:
case read_auto:
    if(!mddev->pers || !md_is_rdwr(mddev))
          break;
    err = mddev_sync_blockdev(mddev);
    if (err)
        return err;
    clear_md_closing = true;
    
>  	err = mddev_lock(mddev);
>  	if (err)
>  		return err;
> @@ -4523,6 +4534,8 @@ array_state_store(struct mddev *mddev, const char *buf,
> size_t len) break;
>  	case clear:
>  		err = do_md_stop(mddev, 0, NULL);
> +		if (!err)
> +			clear_md_closing = false;
>  		break;
>  	case readonly:
>  		if (mddev->pers)
> @@ -4585,6 +4598,8 @@ array_state_store(struct mddev *mddev, const char *buf,
> size_t len) sysfs_notify_dirent_safe(mddev->sysfs_state);
>  	}
>  	mddev_unlock(mddev);
> +	if (clear_md_closing)
> +		clear_bit(MD_CLOSING, &mddev->flags);

Please add spaces before and after if.

>  	return err ?: len;
>  }
>  static struct md_sysfs_entry md_array_state =

Thanks,
Mariusz