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

[Kirill Tkhai]

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?

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;
 }