Re: [PATCH 1/1] sched/numa: Fix memory leak due to the overwritten vma->numab_state

[Raghavendra K T <raghavendra.kt@amd.com>]

On 11/11/2024 3:38 PM, Adrian Huang wrote:
> <snip>
>> However since there are 800 threads, I see there might be an opportunity
>> for another thread to enter in the next 'numa_scan_period' while
>> we have not gotten till numab_state allocation.
>>
>> There should be simpler ways to overcome like Vlastimil already pointed
>> in the other thread, and having lock is an overkill.
>>
>> for e.g.,
>> numab_state = kzalloc(..)
>>
>> if we see that some other thread able to successfully assign
>> vma->numab_state with their allocation (with cmpxchg), simply
>> free your allocation.
>>
>> Can you please check if my understanding is correct?
> 
> Thanks for Vlastimil's and Raghu's reviews and comments.
> 
> Yes, your understanding is correct. Before submitting this patch,
> I had two internal proposals: lock and cmpxchg. Here is the my cmpxchg
> version (Test passed). If you're ok with this cmpxchg version, may I have
> your reviewed-by? I'll send a v2 then.
> 
> ---
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 3356315d7e64..7f99df294583 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3399,10 +3399,16 @@ static void task_numa_work(struct callback_head *work)
>   
>   		/* Initialise new per-VMA NUMAB state. */
>   		if (!vma->numab_state) {
> -			vma->numab_state = kzalloc(sizeof(struct vma_numab_state),
> -				GFP_KERNEL);
> -			if (!vma->numab_state)
> +			struct vma_numab_state *ptr;
> +
> +			ptr = kzalloc(sizeof(*ptr), GFP_KERNEL);
> +			if (!ptr)
> +				continue;
> +
> +			if (cmpxchg(&vma->numab_state, NULL, ptr)) {
> +				kfree(ptr);
>   				continue;
> +			}
>   
>   			vma->numab_state->start_scan_seq = mm->numa_scan_seq;
> 

LGTM. Sure feel free to add

Reviewed-by: Raghavendra K T <raghavendra.kt@amd.com>

Since allocation for numab_state happen only once.. I hope there is not
much impact on the performance also.

Thanks and Regards
- Raghu