linux-kernel - Re: [PATCH 6/7] mm: kill vma flag VM

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Date:	Mon, 2 Apr 2012 22:05:51 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Eric Paris <eparis@...hat.com>
Subject: Re: [PATCH 6/7] mm: kill vma flag VM_EXECUTABLE

On Mon, Apr 02, 2012 at 09:14:44PM +0400, Konstantin Khlebnikov wrote:
...
> >
> >Ah, it's about locking. I misundertand it at first.
> >Oleg, forget about my email then.
> 
> Yes, it's about locking. Please review patch for your code from attachment.

Thanks a lot, Konstantin! This should do the trick.

> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index cff94cd..4a41270 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -437,6 +437,7 @@ extern int get_dumpable(struct mm_struct *mm);
>  					/* leave room for more dump flags */
>  #define MMF_VM_MERGEABLE	16	/* KSM may merge identical pages */
>  #define MMF_VM_HUGEPAGE		17	/* set when VM_HUGEPAGE is set on vma */
> +#define MMF_EXE_FILE_CHANGED	18	/* see prctl(PR_SET_MM_EXE_FILE) */
>  
>  #define MMF_INIT_MASK		(MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)
>  
> diff --git a/kernel/sys.c b/kernel/sys.c
> index da660f3..b217069 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1714,17 +1714,11 @@ static bool vma_flags_mismatch(struct vm_area_struct *vma,
>  
>  static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
>  {
> +	struct vm_area_struct *vma;
>  	struct file *exe_file;
>  	struct dentry *dentry;
>  	int err;
>  
> -	/*
> -	 * Setting new mm::exe_file is only allowed when no VM_EXECUTABLE vma's
> -	 * remain. So perform a quick test first.
> -	 */
> -	if (mm->num_exe_file_vmas)
> -		return -EBUSY;
> -
>  	exe_file = fget(fd);
>  	if (!exe_file)
>  		return -EBADF;
> @@ -1745,17 +1739,28 @@ static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
>  	if (err)
>  		goto exit;
>  
> +	down_write(&mm->mmap_sem);
> +	/*
> +	 * Forbid mm->exe_file change if there are mapped some other files.
> +	 */
> +	err = -EEXIST;
> +	for (vma = mm->mmap; vma; vma = vma->vm_next) {
> +		if (vma->vm_file &&
> +		    !path_equal(&vma->vm_file->f_path, &exe_file->f_path))
> +			goto out_unlock;
> +	}

If I understand right, this snippet is emulating old behaviour (ie as
it was with num_exe_file_vmas), thus -EBUSY might be more appropriate?
But it's really a small nit I think. Thanks again.

	Cyrill
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