linux-kernel - Re: [PATCH 2/3] introduce probe_slab

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Date:	Tue, 28 Oct 2014 08:44:51 +0300
From:	Kirill Tkhai <ktkhai@...allels.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	<linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Kirill Tkhai <tkhai@...dex.ru>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 2/3] introduce probe_slab_address()

В Пн, 27/10/2014 в 20:54 +0100, Oleg Nesterov пишет:
> Extract the ifdef(CONFIG_DEBUG_PAGEALLOC) code from get_freepointer_safe()
> into the new generic helper, probe_slab_address(). The next patch will add
> another user.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  include/linux/uaccess.h |   15 +++++++++++++++
>  mm/slub.c               |    6 +-----
>  2 files changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> index effb637..3367396 100644
> --- a/include/linux/uaccess.h
> +++ b/include/linux/uaccess.h
> @@ -71,6 +71,21 @@ static inline unsigned long __copy_from_user_nocache(void *to,
>  	__probe_kernel_read(&(retval), (__force void *)(addr), sizeof(retval))
>  
>  /*
> + * Same as probe_kernel_address(), but @addr must be the valid pointer
> + * to a slab object, potentially freed/reused/unmapped.
> + */
> +#ifdef CONFIG_DEBUG_PAGEALLOC
> +#define probe_slab_address(addr, retval)	\
> +	probe_kernel_address(addr, retval)
> +#else
> +#define probe_slab_address(addr, retval)	\
> +	({							\
> +		(retval) = *(typeof(retval) *)(addr);		\
> +		0;						\
> +	})
> +#endif
> +
> +/*
>   * probe_kernel_read(): safely attempt to read from a location
>   * @dst: pointer to the buffer that shall take the data
>   * @src: address to read from
> diff --git a/mm/slub.c b/mm/slub.c
> index 3e8afcc..0467d22 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -265,11 +265,7 @@ static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)
>  {
>  	void *p;
>  
> -#ifdef CONFIG_DEBUG_PAGEALLOC
> -	probe_kernel_read(&p, (void **)(object + s->offset), sizeof(p));
> -#else
> -	p = get_freepointer(s, object);
> -#endif
> +	probe_slab_address(object + s->offset, p);
>  	return p;
>  }
>  

probe_kernel_read() was arch-dependent on tree platforms:

arch/blackfin/mm/maccess.c
arch/parisc/lib/memcpy.c
arch/um/kernel/maccess.c

But now we skip these arch-dependent implementations. Is there no a problem?

Kirill

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