Re: [PATCH V2 4/5] erofs: remove duplicated unregister_cookie

[JeffleXu]

On 9/2/22 6:53 PM, Jia Zhu wrote:
> In erofs umount scenario, erofs_fscache_unregister_cookie() is called
> twice in kill_sb() and put_super().
> 
> It works for original semantics, cause 'ctx' will be set to NULL in
> put_super() and will not be unregister again in kill_sb().
> However, in shared domain scenario, we use refcount to maintain the
> lifecycle of cookie. Unregister the cookie twice will cause it to be
> released early.
> 
> For the above reasons, this patch removes duplicate unregister_cookie
> and move fscache_unregister_* before shotdown_super() to prevent busy
> inode(ctx->inode) when umount.
> 
> Signed-off-by: Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>
> ---
>  fs/erofs/super.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 69de1731f454..667a78f0ee70 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -919,19 +919,20 @@ static void erofs_kill_sb(struct super_block *sb)
>  		kill_litter_super(sb);
>  		return;
>  	}
> -	if (erofs_is_fscache_mode(sb))
> -		generic_shutdown_super(sb);
> -	else
> -		kill_block_super(sb);
> -
>  	sbi = EROFS_SB(sb);
>  	if (!sbi)
>  		return;
>  
> +	if (erofs_is_fscache_mode(sb)) {
> +		erofs_fscache_unregister_cookie(&sbi->s_fscache);
> +		erofs_fscache_unregister_fs(sb);
> +		generic_shutdown_super(sb);

Generally we can't do clean ups before generic_shutdown_super(), since
generic_shutdown_super() may trigger IO, e.g. in sync_filesystem(),
though it's not the case for erofs (read-only).

How about embedding erofs_fscache_unregister_cookie() into
erofs_fscache_unregister_fs(), and thus we can check domain_id in
erofs_fscache_unregister_fs()?

> +	} else {
> +		kill_block_super(sb);
> +	}
> +
>  	erofs_free_dev_context(sbi->devs);
>  	fs_put_dax(sbi->dax_dev, NULL);
> -	erofs_fscache_unregister_cookie(&sbi->s_fscache);
> -	erofs_fscache_unregister_fs(sb);
>  	kfree(sbi->opt.fsid);
>  	kfree(sbi->opt.domain_id);
>  	kfree(sbi);
> @@ -951,7 +952,6 @@ static void erofs_put_super(struct super_block *sb)
>  	iput(sbi->managed_cache);
>  	sbi->managed_cache = NULL;
>  #endif
> -	erofs_fscache_unregister_cookie(&sbi->s_fscache);
>  }
>  
>  struct file_system_type erofs_fs_type = {

-- 
Thanks,
Jingbo