[CRIU] [PATCH] flock: blocked processes are not interesting for us

[Pavel Emelyanov]

On 10/31/2014 02:42 PM, Andrey Vagin wrote:
> All out processes are stopped in a moment, when file locks are
> collected, so they can't to wait any locks.
> 
> Here is a proof of this theory:
> [root at avagin-fc19-cr ~]# flock xxx sleep 1000 &
> [1] 23278
> [root at avagin-fc19-cr ~]# flock xxx sleep 1000 &
> [2] 23280
> [root at avagin-fc19-cr ~]# cat /proc/locks
> 1: FLOCK  ADVISORY  WRITE 23278 08:03:280001 0 EOF
> 1: -> FLOCK  ADVISORY  WRITE 23280 08:03:280001 0 EOF
> [root at avagin-fc19-cr ~]# gdb -p 23280
> (gdb) ^Z
> [3]+  Stopped                 gdb -p 23280
> [root at avagin-fc19-cr ~]# cat /proc/locks
> 1: FLOCK  ADVISORY  WRITE 23278 08:03:280001 0 EOF
> 
> Currently criu can dump nothing, if we have one process which is
> waiting a lock. I don't see any reason to do this.
> 
> Cc: Qiang Huang <h.huangqiang at huawei.com>
> Reported-by: Mr Jenkins
> Signed-off-by: Andrey Vagin <avagin at openvz.org>
> ---
>  proc_parse.c | 36 ++++++++++++++++--------------------
>  1 file changed, 16 insertions(+), 20 deletions(-)
> 
> diff --git a/proc_parse.c b/proc_parse.c
> index 389cb72..b1afb61 100644
> --- a/proc_parse.c
> +++ b/proc_parse.c
> @@ -1501,6 +1501,12 @@ int parse_file_locks(void)
>  			goto err;
>  		}
>  
> +		pr_info("lockinfo: %lld:%d %x %d %02x:%02x:%ld %lld %s\n",
> +			fl->fl_id, fl->fl_kind, fl->fl_ltype,
> +			fl->fl_owner, fl->maj, fl->min, fl->i_no,
> +			fl->start, fl->end);
> +
> +
>  		if (fl->fl_kind == FL_UNKNOWN) {
>  			pr_err("Unknown file lock!\n");
>  			ret = -1;
> @@ -1508,6 +1514,16 @@ int parse_file_locks(void)
>  			goto err;
>  		}
>  
> +		if (is_blocked) {
> +			/*
> +			 * All target processes are stopped in this moment and
> +			 * can't wait any locks.
> +			 */
> +			pr_debug("Skip blocked processes\n");
> +			xfree(fl);
> +			goto err;

Why goto err? I thought the intention is to just skip those.

> +		}
> +
>  		if ((fl->fl_kind == FL_POSIX) &&
>  				!pid_in_pstree(fl->fl_owner)) {
>  			/*
> @@ -1519,26 +1535,6 @@ int parse_file_locks(void)
>  			continue;
>  		}
>  
> -		pr_info("lockinfo: %lld:%d %x %d %02x:%02x:%ld %lld %s\n",
> -			fl->fl_id, fl->fl_kind, fl->fl_ltype,
> -			fl->fl_owner, fl->maj, fl->min, fl->i_no,
> -			fl->start, fl->end);
> -
> -		if (is_blocked) {
> -			/*
> -			 * Here the task is in the pstree.
> -			 * If it is blocked on a flock, when we try to
> -			 * ptrace-seize it, the kernel will unblock task
> -			 * from flock and will stop it in another place.
> -			 * So in dumping, a blocked file lock should never
> -			 * be here.
> -			 */
> -			pr_perror("We have a blocked file lock!");
> -			ret = -1;
> -			xfree(fl);
> -			goto err;
> -		}
> -
>  		list_add_tail(&fl->list, &file_lock_list);
>  	}
>  
>