linux-kernel - Re: [PATCH] kmemleak: Only use GFP_KERNEL|GFP

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Message-ID: <84144f020906170601l254d3b29udc688d02426ea247@mail.gmail.com>
Date:	Wed, 17 Jun 2009 16:01:22 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Mel Gorman <mel@....ul.ie>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	torvalds@...ux-foundation.org, fengguang.wu@...el.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kmemleak: Only use GFP_KERNEL|GFP_ATOMIC for the internal 
	allocations

Hi Catalin,

On Wed, Jun 17, 2009 at 3:52 PM, Catalin Marinas<catalin.marinas@....com> wrote:
> Kmemleak allocates memory for pointer tracking and it tries to avoid
> using GFP_ATOMIC if the caller doesn't require it. However other gfp
> flags may be passed by the caller which aren't required by kmemleak.
> This patch filters the gfp flags so that only GFP_KERNEL | GFP_ATOMIC
> are used.
>
> Signed-off-by: Catalin Marinas <catalin.marinas@....com>

Is this really safe? What if we're in a middle of a filesystem
operation that uses GFP_NOFAIL and all of a sudden kmemleak allocation
fails and causes a panic?

                                     Pekka

> ---
>  mm/kmemleak.c |    7 +++++--
>  1 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index 58ec86c..25e2034 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -109,6 +109,9 @@
>
>  #define BYTES_PER_POINTER      sizeof(void *)
>
> +/* GFP bitmask for kmemleak internal allocations */
> +#define GFP_KMEMLEAK_MASK      (GFP_KERNEL | GFP_ATOMIC)
> +
>  /* scanning area inside a memory block */
>  struct kmemleak_scan_area {
>        struct hlist_node node;
> @@ -462,7 +465,7 @@ static void create_object(unsigned long ptr, size_t size, int min_count,
>        struct prio_tree_node *node;
>        struct stack_trace trace;
>
> -       object = kmem_cache_alloc(object_cache, gfp & ~GFP_SLAB_BUG_MASK);
> +       object = kmem_cache_alloc(object_cache, gfp & GFP_KMEMLEAK_MASK);
>        if (!object) {
>                kmemleak_panic("kmemleak: Cannot allocate a kmemleak_object "
>                               "structure\n");
> @@ -636,7 +639,7 @@ static void add_scan_area(unsigned long ptr, unsigned long offset,
>                return;
>        }
>
> -       area = kmem_cache_alloc(scan_area_cache, gfp & ~GFP_SLAB_BUG_MASK);
> +       area = kmem_cache_alloc(scan_area_cache, gfp & GFP_KMEMLEAK_MASK);
>        if (!area) {
>                kmemleak_warn("kmemleak: Cannot allocate a scan area\n");
>                goto out;
>
>
> --
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