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

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Message-ID: <82e15a21-c5ee-45a4-add6-fcb94c6fcc71@suse.cz>
Date: Wed, 13 Nov 2024 19:41:08 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Adrian Huang <adrianhuang0701@...il.com>, raghavendra.kt@....com
Cc: ahuang12@...ovo.com, akpm@...ux-foundation.org, bsegall@...gle.com,
 dietmar.eggemann@....com, juri.lelli@...hat.com,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, mgorman@...e.de,
 mingo@...hat.com, peterz@...radead.org, rostedt@...dmis.org,
 sunjw10@...ovo.com, vincent.guittot@...aro.org, vschneid@...hat.com
Subject: Re: [PATCH 1/1] sched/numa: Fix memory leak due to the overwritten
 vma->numab_state

On 11/11/24 11:08, 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.

Yeah much better, thanks!

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

> ---
> 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;
> 
>