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

[Kirill Tkhai]

On 01.02.2017 04:14, Andrei Vagin wrote:
> On Tue, Jan 31, 2017 at 11:58:13AM +0300, Kirill Tkhai wrote:
>> On 30.01.2017 23:45, Andrei Vagin wrote:
>>> On Sat, Jan 28, 2017 at 06:56:21PM +0300, 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.
>>>
>>> Why is it not aligned without this patch?
>>
>> This patch points that in clear way!
> 
> The C Standard guarantees that all fields in structures aligned, doesn't
> it? I don't have objections about this patch, just to know that I don't
> skip something.

You sure, and patch does not change something in this way.
But it may be a reminder for a person, who changes allocator.
I'm not insist on this.
 
>>
>>>>
>>>> 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;
>>>> +	};
>>>>  	struct pstree_item	*parent;
>>>>  	struct list_head	children;	/* list of my children */
>>>>  	struct list_head	sibling;	/* linkage in my parent's children list */
>>>> @@ -25,10 +30,6 @@ struct pstree_item {
>>>>  	struct pid		*threads;	/* array of threads */
>>>>  	CoreEntry		**core;
>>>>  	TaskKobjIdsEntry	*ids;
>>>> -	union {
>>>> -		futex_t		task_st;
>>>> -		unsigned long	task_st_le_bits;
>>>> -	};
>>>>  };
>>>>  
>>>>  enum {
>>>> diff --git a/criu/pstree.c b/criu/pstree.c
>>>> index 8eeea947c..bee9c8917 100644
>>>> --- a/criu/pstree.c
>>>> +++ b/criu/pstree.c
>>>> @@ -203,6 +203,7 @@ struct pstree_item *__alloc_pstree_item(bool rst)
>>>>  			return NULL;
>>>>  	} else {
>>>>  		sz = sizeof(*item) + sizeof(struct rst_info);
>>>> +		/* Guarantees sizeof(void *) alignment */
>>>>  		item = shmalloc(sz);
>>>>  		if (!item)
>>>>  			return NULL;
>>>>
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