linux-kernel - Re: [PATCH] mm/vmalloc: move 'area->pages' after if statement

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Date:   Fri, 30 Aug 2019 13:50:07 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Austin Kim <austindh.kim@...il.com>
Cc:     urezki@...il.com, guro@...com, rpenyaev@...e.de, mhocko@...e.com,
        rick.p.edgecombe@...el.com, rppt@...ux.ibm.com,
        aryabinin@...tuozzo.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/vmalloc: move 'area->pages' after if statement

On Fri, 30 Aug 2019 12:57:16 +0900 Austin Kim <austindh.kim@...il.com> wrote:

> If !area->pages statement is true where memory allocation fails, 
> area is freed.
> 
> In this case 'area->pages = pages' should not executed.
> So move 'area->pages = pages' after if statement.
> 
> ...
>
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2416,13 +2416,15 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
>  	} else {
>  		pages = kmalloc_node(array_size, nested_gfp, node);
>  	}
> -	area->pages = pages;
> -	if (!area->pages) {
> +
> +	if (!pages) {
>  		remove_vm_area(area->addr);
>  		kfree(area);
>  		return NULL;
>  	}
>  
> +	area->pages = pages;
> +
>  	for (i = 0; i < area->nr_pages; i++) {
>  		struct page *page;
>  

Fair enough.  But we can/should also do this?

--- a/mm/vmalloc.c~mm-vmalloc-move-area-pages-after-if-statement-fix
+++ a/mm/vmalloc.c
@@ -2409,7 +2409,6 @@ static void *__vmalloc_area_node(struct
 	nr_pages = get_vm_area_size(area) >> PAGE_SHIFT;
 	array_size = (nr_pages * sizeof(struct page *));
 
-	area->nr_pages = nr_pages;
 	/* Please note that the recursion is strictly bounded. */
 	if (array_size > PAGE_SIZE) {
 		pages = __vmalloc_node(array_size, 1, nested_gfp|highmem_mask,
@@ -2425,6 +2424,7 @@ static void *__vmalloc_area_node(struct
 	}
 
 	area->pages = pages;
+	area->nr_pages = nr_pages;
 
 	for (i = 0; i < area->nr_pages; i++) {
 		struct page *page;
_