linux-kernel - Re: [RFC/PATCH] mm/futex: Fix futex writes on archs with SW tracking of dirty & young

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Date:	Wed, 27 Jul 2011 20:20:43 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	David Howells <dhowells@...hat.com>,
	Mike Frysinger <vapier.adi@...il.com>,
	Shan Hai <haishan.bai@...il.com>, paulus@...ba.org,
	tglx@...utronix.de, walken@...gle.com, cmetcalf@...era.com,
	tony.luck@...el.com, akpm@...ux-foundation.org,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	uclinux-dist-devel@...ckfin.uclinux.org
Subject: Re: [RFC/PATCH] mm/futex: Fix futex writes on archs with SW
 tracking of dirty & young

On Wed, 2011-07-27 at 12:17 +0200, Peter Zijlstra wrote:
> On Wed, 2011-07-27 at 11:09 +0100, David Howells wrote:
> > Can you inline this for the NOMMU case please?
> 
> ---
> Subject: mm: Fix fixup_user_fault() for MMU=n 
> 
> In commit 2efaca927 ("mm/futex: fix futex writes on archs with SW
> tracking of dirty & young") we forgot about MMU=n. This patch fixes
> that.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

Hoping the BUG() isn't trippable by userspace but then it's no mmu, it's
not like we care what userspace can do right :-)

Acked-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>

Thanks !

Cheers,
Ben.

> ---
> Index: linux-2.6/include/linux/mm.h
> ===================================================================
> --- linux-2.6.orig/include/linux/mm.h
> +++ linux-2.6/include/linux/mm.h
> @@ -962,6 +962,8 @@ int invalidate_inode_page(struct page *p
>  #ifdef CONFIG_MMU
>  extern int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>  			unsigned long address, unsigned int flags);
> +extern int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
> +			    unsigned long address, unsigned int fault_flags);
>  #else
>  static inline int handle_mm_fault(struct mm_struct *mm,
>  			struct vm_area_struct *vma, unsigned long address,
> @@ -971,6 +973,14 @@ static inline int handle_mm_fault(struct
>  	BUG();
>  	return VM_FAULT_SIGBUS;
>  }
> +static inline int fixup_user_fault(struct task_struct *tsk, 
> +		struct mm_struct *mm, unsigned long address,
> +		unsigned int fault_flags)
> +{
> +	/* should never happen if there's no MMU */
> +	BUG();
> +	return -EFAULT;
> +}
>  #endif
>  
>  extern int make_pages_present(unsigned long addr, unsigned long end);
> @@ -988,8 +998,6 @@ int get_user_pages(struct task_struct *t
>  int get_user_pages_fast(unsigned long start, int nr_pages, int write,
>  			struct page **pages);
>  struct page *get_dump_page(unsigned long addr);
> -extern int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
> -			    unsigned long address, unsigned int fault_flags);
>  
>  extern int try_to_release_page(struct page * page, gfp_t gfp_mask);
>  extern void do_invalidatepage(struct page *page, unsigned long offset);
> 
> --
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