[CRIU] [PATCH v2] pstree: bump kernel pid_max value if needed

[Laurent Dufour]

On 21/07/2016 19:04, Pavel Emelyanov wrote:
> On 07/19/2016 07:45 PM, Laurent Dufour wrote:
>> When restoring on a different node, it may happen that pid_max is
>> below one of the pid we wanted to recreate.
>> This leads to a restore error when cloning the restarted process:
>>
>> (00.011172) Forking task with 44794 pid (flags 0x0)
>> (00.011205) Error (cr-restore.c:1008): 44794: Write 44793 to sys/kernel/ns_last_pid: Invalid argument
>>
>> This patch computes the largest pid value and sets the kernel pid_max if
>> necessary.
>>
>> If the user don't have the permission to do so, the restart is
>> failing mentioning that we can't push the pid_max limit.
>>
>> Signed-off-by: Laurent Dufour <ldufour at linux.vnet.ibm.com>
>> ---
>>
>> v2: don't print the push statement if write() has failed
>>
>>  criu/pstree.c | 44 ++++++++++++++++++++++++++++++++++++++++++--
>>  1 file changed, 42 insertions(+), 2 deletions(-)
>>
>> diff --git a/criu/pstree.c b/criu/pstree.c
>> index c2fa7486683a..dde5d5a1e779 100644
>> --- a/criu/pstree.c
>> +++ b/criu/pstree.c
>> @@ -474,7 +474,7 @@ static int read_pstree_ids(struct pstree_item *pi)
>>  	return 0;
>>  }
>>  
>> -static int read_pstree_image(void)
>> +static int read_pstree_image(pid_t *pid_max)
>>  {
>>  	int ret = 0, i;
>>  	struct cr_img *img;
>> @@ -511,8 +511,14 @@ static int read_pstree_image(void)
>>  			break;
>>  
>>  		pi->pid.virt = e->pid;
>> +		if (e->pid > *pid_max)
>> +			*pid_max = e->pid;
>>  		pi->pgid = e->pgid;
>> +		if (e->pgid > *pid_max)
>> +			*pid_max = e->pgid;
>>  		pi->sid = e->sid;
>> +		if (e->sid > *pid_max)
>> +			*pid_max = e->sid;
>>  		pi->pid.state = TASK_ALIVE;
>>  
>>  		if (e->ppid == 0) {
>> @@ -978,8 +984,42 @@ static int prepare_pstree_for_unshare(void)
>>  int prepare_pstree(void)
>>  {
>>  	int ret;
>> +	pid_t pid_max = 0, kpid_max = 0;
>> +	int fd;
>> +	char buf[20];
>> +
>> +	fd = open("/proc/sys/kernel/pid_max", O_RDONLY);
> 
> Can you tune this (and the similar call below) to use the open_proc()
> helpers like it's done for LAST_PID_PATH?

Hi Pavel,

I missed that open_proc can be used to open not self or pid relative
files, I'll send a new version asap.

Thanks,
Laurent.