[CRIU] [PATCH v2] user_ns: Block SIGCHLD during namespaces generation

[Kirill Tkhai]

On 04.04.2017 02:57, Andrei Vagin wrote:
> On Sat, Apr 01, 2017 at 04:05:40PM +0300, Kirill Tkhai wrote:
>> We don't want asynchronous signal handler does wait()
>> as we do that synchronous. So block the signal.
>>
>> v2: Set initial ret = 0
>>
>> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
>> ---
>>  criu/namespaces.c |   21 ++++++++++++++++++++-
>>  1 file changed, 20 insertions(+), 1 deletion(-)
>>
>> diff --git a/criu/namespaces.c b/criu/namespaces.c
>> index 6637abcb..5e71a3a9 100644
>> --- a/criu/namespaces.c
>> +++ b/criu/namespaces.c
>> @@ -2257,7 +2257,26 @@ static int create_user_ns_hierarhy_fn(void *in_arg)
>>  static int create_user_ns_hierarhy(void)
>>  {
>>  	struct ns_arg arg = { .me = root_user_ns };
>> -	return create_user_ns_hierarhy_fn(&arg);
>> +	sigset_t blockmask, oldmask;
>> +	int ret = 0;
>> +
>> +	sigemptyset(&blockmask);
>> +	sigaddset(&blockmask, SIGCHLD);
>> +
>> +	if (sigprocmask(SIG_BLOCK, &blockmask, &oldmask) == -1) {
>> +		pr_perror("Can not set mask of blocked signals");
>> +		return -1;
>> +	}
> 
> Looks like we have to block sigchld in restore_task_with_children() to
> cover all other cases. What do you think about this?

If we did that, we wouldn't have emergency abort in case of a child exits.
Though, generation of ns tree is a special case. We don't want make it be
handled via sigchld_handler(), do we? We may introduce one more temporary
handler or even overload cr_restore.c::sigchld_handler(), but I'm not sure
it's the best solution. What do you think?
 
>> +
>> +	if (create_user_ns_hierarhy_fn(&arg))
>> +		ret = -1;
>> +
>> +	if (sigprocmask(SIG_SETMASK, &oldmask, NULL) == -1) {
>> +		pr_perror("Can not unset mask of blocked signals");
>> +		ret = -1;
>> +	}
>> +
>> +	return ret;
>>  }
>>  
>>  int prepare_namespace(struct pstree_item *item, unsigned long clone_flags)
>>