[CRIU] [PATCH 1/2] rst-malloc: return aligned pointers to sizeof(void *) (v3)

[Pavel Emelyanov]

On 02/04/2016 07:25 PM, Andrew Vagin wrote:
> On Wed, Feb 03, 2016 at 02:07:30PM +0300, Pavel Emelyanov wrote:
>> On 01/27/2016 08:29 PM, Andrew Vagin wrote:
>>> On Wed, Jan 27, 2016 at 04:29:43PM +0300, Pavel Emelyanov wrote:
>>>> On 01/26/2016 10:58 PM, Andrey Vagin wrote:
>>>>> From: Andrew Vagin <avagin at virtuozzo.com>
>>>>>
>>>>> Stas found that if we don't align a pointer,
>>>>> futex and atomic operations can fail.
>>>>>
>>>>> v2: don't hard-code the size of void *
>>>>> v3: add a function to allocate memory without gaps with
>>>>>     a privious slice. It's used to allocate arrays.
>>>>>
>>>>> Cc: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
>>>>> Signed-off-by: Andrew Vagin <avagin at virtuozzo.com>
>>>>> ---
>>>>>  include/rst-malloc.h |  1 +
>>>>>  rst-malloc.c         | 23 ++++++++++++++++++++++-
>>>>>  2 files changed, 23 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/include/rst-malloc.h b/include/rst-malloc.h
>>>>> index 8c48f27..f205622 100644
>>>>> --- a/include/rst-malloc.h
>>>>> +++ b/include/rst-malloc.h
>>>>> @@ -58,6 +58,7 @@ extern void *rst_mem_remap_ptr(unsigned long pos, int type);
>>>>>   * last object can be freed (pop-ed from buffer).
>>>>>   */
>>>>>  extern void *rst_mem_alloc(unsigned long size, int type);
>>>>> +extern void *rst_mem_alloc_cont(unsigned long size, int type);
>>>>>  extern void rst_mem_free_last(int type);
>>>>>  /*
>>>>>   * Routines to remap SHREMAP and PRIVATE into restorer address space
>>>>> diff --git a/rst-malloc.c b/rst-malloc.c
>>>>> index 14e0b41..7685430 100644
>>>>> --- a/rst-malloc.c
>>>>> +++ b/rst-malloc.c
>>>>> @@ -128,6 +128,9 @@ unsigned long rst_mem_cpos(int type)
>>>>>  {
>>>>>  	struct rst_mem_type_s *t = &rst_mems[type];
>>>>>  	BUG_ON(!t->remapable || !t->enabled);
>>>>> +
>>>>> +	t->free_mem = (void *) round_up((unsigned long)t->free_mem, sizeof(void *));
>>>>
>>>> Should this hunk be here? Why?
>>>
>>> Yes, it should. We want to aligne a start address of arrays. It's about
>>> a case when rst_mem_alloc_cont is used.
>>
>> It's wrong place for such a thing. The rst_mem_cpos() should be "pure function",
>> i.e. do not change anything inside.
> 
> Where is the right place?

How about introducing a call rst_mem_align() that would make sure the
current posision is aligned, so that any subsequent _cpos() or _alloc()
call would return the aligned pointer?

-- Pavel