linux-kernel - Re: [PATCH] mm: convert three more cases to kvmalloc

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Date:   Thu, 29 Jun 2017 09:10:46 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andreas Dilger <adilger@...ger.ca>,
        John Hubbard <jhubbard@...dia.com>,
        David Miller <davem@...emloft.net>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: convert three more cases to kvmalloc

On Wed 28-06-17 23:24:10, Mikulas Patocka wrote:
[...]
> From: Mikulas Patocka <mpatocka@...hat.com>
> 
> The patch a7c3e901 ("mm: introduce kv[mz]alloc helpers") converted a lot 
> of kernel code to kvmalloc. This patch converts three more forgotten 
> cases.

Thanks! I have two remarks below but other than that feel free to add

> Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>

Acked-by: Michal Hocko <mhocko@...e.com>
[...]
> Index: linux-2.6/kernel/bpf/syscall.c
> ===================================================================
> --- linux-2.6.orig/kernel/bpf/syscall.c
> +++ linux-2.6/kernel/bpf/syscall.c
> @@ -58,16 +58,7 @@ void *bpf_map_area_alloc(size_t size)
>  	 * trigger under memory pressure as we really just want to
>  	 * fail instead.
>  	 */
> -	const gfp_t flags = __GFP_NOWARN | __GFP_NORETRY | __GFP_ZERO;
> -	void *area;
> -
> -	if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
> -		area = kmalloc(size, GFP_USER | flags);
> -		if (area != NULL)
> -			return area;
> -	}
> -
> -	return __vmalloc(size, GFP_KERNEL | flags, PAGE_KERNEL);
> +	return kvmalloc(size, GFP_USER | __GFP_NOWARN | __GFP_NORETRY | __GFP_ZERO);

kvzalloc without additional flags would be more appropriate.
__GFP_NORETRY is explicitly documented as non-supported and NOWARN
wouldn't be applied everywhere in the vmalloc path.

>  }
>  
>  void bpf_map_area_free(void *area)
> Index: linux-2.6/kernel/cgroup/cgroup-v1.c
> ===================================================================
> --- linux-2.6.orig/kernel/cgroup/cgroup-v1.c
> +++ linux-2.6/kernel/cgroup/cgroup-v1.c
> @@ -184,15 +184,10 @@ struct cgroup_pidlist {
>  /*
>   * The following two functions "fix" the issue where there are more pids
>   * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
> - * TODO: replace with a kernel-wide solution to this problem
>   */
> -#define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
>  static void *pidlist_allocate(int count)
>  {
> -	if (PIDLIST_TOO_LARGE(count))
> -		return vmalloc(count * sizeof(pid_t));
> -	else
> -		return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
> +	return kvmalloc(count * sizeof(pid_t), GFP_KERNEL);
>  }

I would rather use kvmalloc_array to have an overflow protection as
well.

>  
>  static void pidlist_free(void *p)

-- 
Michal Hocko
SUSE Labs