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

[Ruslan Kuprieiev]

On 12/02/2014 03:20 PM, Pavel Emelyanov wrote:
> 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).
>

Ah, i see.
Thanks.

>>   		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 {
>>
>