[PATCH] mm/vmalloc: Add check for KMEM_CACHE

[PATCH] mm/vmalloc: Add check for KMEM_CACHE

[Jiasheng Jiang]

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.

Fixes: 68ad4a330433 ("mm/vmalloc.c: keep track of free blocks for vmap allocation")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.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

Re: [PATCH] mm/vmalloc: Add check for KMEM_CACHE

[Matthew Wilcox]

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@iscas.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
> 
> 

Re: [PATCH] mm/vmalloc: Add check for KMEM_CACHE

[Andrew Morton]

On Thu, 24 Nov 2022 12:02:26 +0800 Jiasheng Jiang <jiasheng@iscas.ac.cn> 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.
> 
> ...
>
> @@ -2426,15 +2426,17 @@ void __init vmalloc_init(void)

Linux assumes that allocation attempts from __init code will succeed.

Because if they fail so early in the boot process, the system is so
utterly messed up that we may as well just go oops.