[CRIU] [PATCH 3/8] cr-restore: set cr_error to EEXIST if such pid already exists, v2

[Pavel Emelyanov]

On 12/02/2014 03:29 PM, Ruslan Kuprieiev wrote:
> This is a very common error when using criu.
> 
> The problem here is that we need to somehow transfer cr_errno
> from one process to another. I suggest using pipe to give
> one end to children and read cr_errno on other after restore
> is finished.
> 
> v2, Pavel suggested putting errno into shared task_entries.
> 
> Signed-off-by: Ruslan Kuprieiev <kupruser at gmail.com>
> ---
>  cr-restore.c       | 7 ++++++-
>  include/cr-errno.h | 1 +
>  include/rst_info.h | 1 +
>  3 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/cr-restore.c b/cr-restore.c
> index 93a6ca6..60641d9 100644
> --- a/cr-restore.c
> +++ b/cr-restore.c
> @@ -85,6 +85,8 @@
>  
>  #include "asm/restore.h"
>  
> +#include "cr-errno.h"
> +
>  static struct pstree_item *current;
>  
>  static int restore_task_with_children(void *);
> @@ -1412,6 +1414,7 @@ static int restore_task_with_children(void *_arg)
>  	pid = getpid();
>  	if (current->pid.virt != pid) {
>  		pr_err("Pid %d do not match expected %d\n", pid, current->pid.virt);
> +		task_entries->cr_err = EEXIST;

This is racy. Presumably we want to get the very first error from
children, thus we need the cmpxchg() here (wrapped in a helper).

>  		goto err;
>  	}
>  
> @@ -1535,8 +1538,10 @@ static int restore_wait_inprogress_tasks()
>  
>  	futex_wait_while_gt(np, 0);
>  	ret = (int)futex_get(np);
> -	if (ret < 0)
> +	if (ret < 0) {
> +		cr_errno = task_entries->cr_err;
>  		return ret;
> +	}
>  
>  	return 0;
>  }
> diff --git a/include/cr-errno.h b/include/cr-errno.h
> index bec72a8..f86bba8 100644
> --- a/include/cr-errno.h
> +++ b/include/cr-errno.h
> @@ -4,6 +4,7 @@ extern int cr_errno;
>  /*
>   * List of symbolic error names:
>   * ESRCH	- no process can be found corresponding to that specified by pid
> + * EEXIST	- process with such pid already exists
>   */
>  
>  #endif /* __CR_ERRNO_H__ */
> diff --git a/include/rst_info.h b/include/rst_info.h
> index 6b00c50..cec0144 100644
> --- a/include/rst_info.h
> +++ b/include/rst_info.h
> @@ -10,6 +10,7 @@ struct task_entries {
>  	futex_t nr_in_progress;
>  	futex_t start;
>  	mutex_t	zombie_lock;
> +	int cr_err;
>  };
>  
>  struct fdt {
>