linux-kernel - Re: [PATCH 4/4] kmemcheck v4

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Date:	Thu, 14 Feb 2008 22:12:20 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Vegard Nossum <vegard.nossum@...il.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Daniel Walker <dwalker@...sta.com>,
	Ingo Molnar <mingo@...e.hu>,
	Richard Knutsson <ricknu-0@...dent.ltu.se>,
	Andi Kleen <andi@...stfloor.org>,
	Christoph Lameter <clameter@....com>
Subject: Re: [PATCH 4/4] kmemcheck v4

Hi,

Vegard Nossum wrote:
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 412672a..7bdb37f 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -1294,7 +1294,11 @@ static inline void __skb_queue_purge(struct 
> sk_buff_head *list)
>  static inline struct sk_buff *__dev_alloc_skb(unsigned int length,
>                            gfp_t gfp_mask)
>  {
> -    struct sk_buff *skb = alloc_skb(length + NET_SKB_PAD, gfp_mask);
> +    struct sk_buff *skb;
> +#ifdef CONFIG_KMEMCHECK
> +    gfp_mask |= __GFP_ZERO;
> +#endif

Use __GFP_NOTRACK here (no need to wrap it in CONFIG_KMEMCHECK either).

> +    skb = alloc_skb(length + NET_SKB_PAD, gfp_mask);
>      if (likely(skb))
>          skb_reserve(skb, NET_SKB_PAD);
>      return skb;

> diff --git a/init/do_mounts.c b/init/do_mounts.c
> index f865731..87b1b0f 100644
> --- a/init/do_mounts.c
> +++ b/init/do_mounts.c
> @@ -201,9 +201,13 @@ static int __init do_mount_root(char *name, char 
> *fs, int flags, void *data)
>      return 0;
>  }
> 
> +#if PAGE_SIZE < PATH_MAX
> +# error increase the fs_names allocation size here
> +#endif
> +
>  void __init mount_block_root(char *name, int flags)
>  {
> -    char *fs_names = __getname();
> +    char *fs_names = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
>      char *p;
>  #ifdef CONFIG_BLOCK
>      char b[BDEVNAME_SIZE];
> @@ -251,7 +255,7 @@ retry:
>  #endif
>      panic("VFS: Unable to mount root fs on %s", b);
>  out:
> -    putname(fs_names);
> +    free_pages((unsigned long)fs_names, 1);

As discussed before, I don't think kmemcheck should be complaining about 
this (even though this is a potential bug). Have you tried with the 
current patches to see if it still triggers? Could have been one of the 
kmemcheck bugs, no?

> @@ -255,6 +258,9 @@ struct sk_buff *__netdev_alloc_skb(struct net_device 
> *dev,
>      int node = dev->dev.parent ? dev_to_node(dev->dev.parent) : -1;
>      struct sk_buff *skb;
> 
> +#ifdef CONFIG_KMEMCHECK
> +    gfp_mask |= __GFP_ZERO;
> +#endif

__GFP_NOTRACK here

			Pekka
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