[CRIU] [PATCH 07/11] restore: add a function to wait when other tasks finish a stage

[Pavel Emelyanov]

On 02/09/2017 04:03 AM, Andrei Vagin wrote:
> On Wed, Feb 08, 2017 at 12:51:05PM +0300, Pavel Emelyanov wrote:
>> On 02/02/2017 03:04 AM, Andrei Vagin wrote:
>>> From: Andrei Vagin <avagin at virtuozzo.com>
>>>
>>> It is used now to close descriptors of mount namespaces
>>> and will be used for network namespaces too.
>>>
>>> Signed-off-by: Andrei Vagin <avagin at virtuozzo.com>
>>> ---
>>>  criu/cr-restore.c | 28 +++++++++++++++++++++++++++-
>>>  1 file changed, 27 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/criu/cr-restore.c b/criu/cr-restore.c
>>> index ba8ee57..681655d 100644
>>> --- a/criu/cr-restore.c
>>> +++ b/criu/cr-restore.c
>>> @@ -119,6 +119,7 @@ static int prepare_rlimits(int pid, struct task_restore_args *, CoreEntry *core)
>>>  static int prepare_posix_timers(int pid, struct task_restore_args *ta, CoreEntry *core);
>>>  static int prepare_signals(int pid, struct task_restore_args *, CoreEntry *core);
>>>  
>>> +static void restore_wait_other_tasks();
>>>  
>>>  static int crtools_prepare_shared(void)
>>>  {
>>> @@ -1474,7 +1475,7 @@ static int restore_task_with_children(void *_arg)
>>>  		 * Wait when all tasks passed the CR_STATE_FORKING stage.
>>>  		 * It means that all tasks entered into their namespaces.
>>>  		 */
>>> -		futex_wait_while_gt(&task_entries->nr_in_progress, 1);
>>> +		restore_wait_other_tasks();
>>>  
>>>  		fini_restore_mntns();
>>>  	}
>>> @@ -1518,6 +1519,19 @@ static inline int stage_participants(int next_stage)
>>>  	return -1;
>>>  }
>>>  
>>> +static inline int stage_current_participants(int next_stage)
>>> +{
>>> +	switch (next_stage) {
>>> +	case CR_STATE_FORKING:
>>> +		return 1;
>>
>> Waiting for nr_in_progress to become 1 (or less) makes sense, but ...
>>
>>> +	case CR_STATE_RESTORE:
>>> +		return current->nr_threads;
>>
>> Why this???
> 
> Wait all tasks except the current one. Threads are created on this stage
> and each thread has to report at the end of this stage.

I don't get this explanation :( nr_threads account for threads across all
tasks, not only the current one.

>>
>>> +	}
>>> +
>>> +	BUG();
>>> +	return -1;
>>> +}
>>> +
>>>  static int restore_wait_inprogress_tasks()
>>>  {
>>>  	int ret;
>>> @@ -1546,6 +1560,18 @@ static int restore_switch_stage(int next_stage)
>>>  	return restore_wait_inprogress_tasks();
>>>  }
>>>  
>>> +/* Wait all tasks except the current one */
>>> +static void restore_wait_other_tasks()
>>> +{
>>> +	int participants, stage;
>>> +
>>> +	stage = futex_get(&task_entries->start);
>>> +	participants = stage_current_participants(stage);
>>> +
>>> +	futex_wait_while_gt(&task_entries->nr_in_progress,
>>> +				participants);
>>> +}
>>> +
>>>  static int attach_to_tasks(bool root_seized)
>>>  {
>>>  	struct pstree_item *item;
>>>
>>
> .
>