[Devel] Re: [RFC PATCH 1/2] mm: move destroy_mm into mmap.c and remove len check

[Oren Laadan]

Both applied, thanks.

Serge E. Hallyn wrote:
> Break do_munmap into two pieces, so we can avoid the check
> for > TASK_SIZE in destroy_mm(), when we trust the vmas are
> proper.
> 
> Really I wonder whether we can pull a lot more out of the
> fn used by destroy_mm: is there really a need to be looking
> whether we need to split vmas?  We always send in one full
> vma at a time, so maybe we should just be calling
> detach_vmas_to_be_unmapped() and unmap_region() by hand?
> 
> this makes 32-bit tasks on x86-64 with COMPAT_VDSO work again.
> It also gets us passed the munmap -EINVAL when restart_64
> restarts a 32-bit image and unloads its own 64-bit vmas.
> 
> (But there is still a 
> 
> 	ckpt[2446] general protection ip:ffffe42f sp:ffc9304c error:0
> 
> with that case)
> 
> Signed-off-by: Serge E. Hallyn <serue at us.ibm.com>
> ---
>  checkpoint/memory.c |   18 ------------------
>  include/linux/mm.h  |    1 +
>  mm/mmap.c           |   38 ++++++++++++++++++++++++++++++++++----
>  3 files changed, 35 insertions(+), 22 deletions(-)
> 
> diff --git a/checkpoint/memory.c b/checkpoint/memory.c
> index f907b88..d51f94b 100644
> --- a/checkpoint/memory.c
> +++ b/checkpoint/memory.c
> @@ -1205,24 +1205,6 @@ static int restore_vma(struct ckpt_ctx *ctx, struct mm_struct *mm)
>  	return ret;
>  }
>  
> -static int destroy_mm(struct mm_struct *mm)
> -{
> -	struct vm_area_struct *vmnext = mm->mmap;
> -	struct vm_area_struct *vma;
> -	int ret;
> -
> -	while (vmnext) {
> -		vma = vmnext;
> -		vmnext = vmnext->vm_next;
> -		ret = do_munmap(mm, vma->vm_start, vma->vm_end-vma->vm_start);
> -		if (ret < 0) {
> -			pr_warning("c/r: failed do_munmap (%d)\n", ret);
> -			return ret;
> -		}
> -	}
> -	return 0;
> -}
> -
>  static struct mm_struct *do_restore_mm(struct ckpt_ctx *ctx)
>  {
>  	struct ckpt_hdr_mm *h;
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index dc34b87..4485296 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1168,6 +1168,7 @@ out:
>  }
>  
>  extern int do_munmap(struct mm_struct *, unsigned long, size_t);
> +extern int destroy_mm(struct mm_struct *);
>  
>  extern unsigned long do_brk(unsigned long, unsigned long);
>  
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 0b2319f..15afae6 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1890,14 +1890,11 @@ int split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
>   * work.  This now handles partial unmappings.
>   * Jeremy Fitzhardinge <jeremy at goop.org>
>   */
> -int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
> +int do_munmap_nocheck(struct mm_struct *mm, unsigned long start, size_t len)
>  {
>  	unsigned long end;
>  	struct vm_area_struct *vma, *prev, *last;
>  
> -	if ((start & ~PAGE_MASK) || start > TASK_SIZE || len > TASK_SIZE-start)
> -		return -EINVAL;
> -
>  	if ((len = PAGE_ALIGN(len)) == 0)
>  		return -EINVAL;
>  
> @@ -1961,8 +1958,41 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
>  	return 0;
>  }
>  
> +int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
> +{
> +	unsigned long end;
> +	struct vm_area_struct *vma, *prev, *last;
> +
> +	if ((start & ~PAGE_MASK) || start > TASK_SIZE || len > TASK_SIZE-start)
> +		return -EINVAL;
> +
> +	return do_munmap_nocheck(mm, start, len);
> +}
> +
>  EXPORT_SYMBOL(do_munmap);
>  
> +/*
> + * called with mm->mmap-sem held
> + * only called from checkpoint/memory.c:restore_mm()
> + */
> +int destroy_mm(struct mm_struct *mm) {
> +	struct vm_area_struct *vmnext = mm->mmap;
> +	struct vm_area_struct *vma;
> +	int ret;
> +
> +	while (vmnext) {
> +		vma = vmnext;
> +		vmnext = vmnext->vm_next;
> +		ret = do_munmap_nocheck(mm, vma->vm_start,
> +					vma->vm_end-vma->vm_start);
> +		if (ret < 0) {
> +			pr_warning("%s: failed munmap (%d)\n", __func__, ret);
> +			return ret;
> +		}
> +	}
> +	return 0;
> +}
> +
>  SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
>  {
>  	int ret;
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