linux-kernel - Re: [PATCH] mm/vmalloc: Add check for KMEM

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Date:   Thu, 24 Nov 2022 04:25:25 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Jiasheng Jiang <jiasheng@...as.ac.cn>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/vmalloc: Add check for KMEM_CACHE

On Thu, Nov 24, 2022 at 12:02:26PM +0800, Jiasheng Jiang wrote:
> As KMEM_CACHE may return NULL pointer, it should
> be better to check the return value in order to
> avoid NULL pointer dereference in kmem_cache_zalloc.

You've made the code more complex.  And for what?  If that
call fails, the system will not boot under any circumstances.

NAK this patch, and any more like it.

> Fixes: 68ad4a330433 ("mm/vmalloc.c: keep track of free blocks for vmap allocation")
> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
> ---
>  mm/vmalloc.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index ccaa461998f3..df3e59f614cc 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2426,15 +2426,17 @@ void __init vmalloc_init(void)
>  	}
>  
>  	/* Import existing vmlist entries. */
> -	for (tmp = vmlist; tmp; tmp = tmp->next) {
> -		va = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
> -		if (WARN_ON_ONCE(!va))
> -			continue;
> +	if (!WARN_ON_ONCE(!vmap_area_cachep)) {
> +		for (tmp = vmlist; tmp; tmp = tmp->next) {
> +			va = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
> +			if (WARN_ON_ONCE(!va))
> +				continue;
>  
> -		va->va_start = (unsigned long)tmp->addr;
> -		va->va_end = va->va_start + tmp->size;
> -		va->vm = tmp;
> -		insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
> +			va->va_start = (unsigned long)tmp->addr;
> +			va->va_end = va->va_start + tmp->size;
> +			va->vm = tmp;
> +			insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
> +		}
>  	}
>  
>  	/*
> -- 
> 2.25.1
> 
>