[CRIU] [PATCH] pstree: Aligned pstree item allocation

[Pavel Emelyanov]

On 02/01/2017 05:15 PM, Kirill Tkhai wrote:
> On 01.02.2017 17:12, Pavel Emelyanov wrote:
>> On 01/28/2017 06:56 PM, Kirill Tkhai wrote:
>>> According to man futex(2):
>>>
>>>     "On all platforms, futexes are four-byte integers
>>>      that must be aligned on a four-byte boundary".
>>>
>>> So, allocate them aligned.
>>>
>>> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
>>> ---
>>>  criu/include/pstree.h |    9 +++++----
>>>  criu/pstree.c         |    1 +
>>>  2 files changed, 6 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/criu/include/pstree.h b/criu/include/pstree.h
>>> index b4dc6b635..ee46a14db 100644
>>> --- a/criu/include/pstree.h
>>> +++ b/criu/include/pstree.h
>>> @@ -12,6 +12,11 @@
>>>   */
>>>  #define INIT_PID	(1)
>>>  struct pstree_item {
>>> +	union {
>>> +		/* Must be 4 bytes aligned */
>>> +		futex_t		task_st;
>>> +		unsigned long	task_st_le_bits;
>>> +	};
>>
>> Ugh... Can't we make this more kernel-style? With the gcc attribute.
> 
> It's a reminder, that the futex must be aligned. The note against
> unaligned *pstree_item* allocation. Maybe, for the time, when someone
> decides to change pstree_item allocation.
> 
> Hm, maybe it'd be better to add something like this instead of the patch?

No, let's pick the __aligned() macro from kernel and mark futex-es with it.

> diff --git a/criu/pstree.c b/criu/pstree.c
> index 6daf4069a..6d980c461 100644
> --- a/criu/pstree.c
> +++ b/criu/pstree.c
> @@ -221,6 +221,7 @@ struct pstree_item *__alloc_pstree_item(bool rst)
>  	item->born_sid = -1;
>  	futex_init(&item->task_st);
>  	item->pid->item = item;
> +	BUG_ON(item & 3); /* Futex should be aligned */
>  
>  	return item;
>  }
> .
>