Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1231515

Re: Multiple potential races on vma->vm_flags

Show all headers | View raw

On 09/23, Oleg Nesterov wrote:
>
> On 09/11, Kirill A. Shutemov wrote:
> >
> > This one is tricky. I *assume* the mm cannot be generally accessible after
> > mm_users drops to zero, but I'm not entirely sure about it.
> > procfs? ptrace?
>
> Well, all I can say is that proc/ptrace look fine afaics...
>
> This is off-topic, but how about the patch below? Different threads can
> expand different vma's at the same time under read_lock(mmap_sem), so
> vma_lock_anon_vma() can't help to serialize "locked_vm += grow".

perhaps vm_stat_account() should be moved too, but total_vm/etc is less
important.

Or I missed something?

Oleg.

> --- x/mm/mmap.c
> +++ x/mm/mmap.c
> @@ -2146,9 +2146,6 @@ static int acct_stack_growth(struct vm_a
>  	if (security_vm_enough_memory_mm(mm, grow))
>  		return -ENOMEM;
>  
> -	/* Ok, everything looks good - let it rip */
> -	if (vma->vm_flags & VM_LOCKED)
> -		mm->locked_vm += grow;
>  	vm_stat_account(mm, vma->vm_flags, vma->vm_file, grow);
>  	return 0;
>  }
> @@ -2210,6 +2207,8 @@ int expand_upwards(struct vm_area_struct
>  				 * against concurrent vma expansions.
>  				 */
>  				spin_lock(&vma->vm_mm->page_table_lock);
> +				if (vma->vm_flags & VM_LOCKED)
> +					mm->locked_vm += grow;
>  				anon_vma_interval_tree_pre_update_vma(vma);
>  				vma->vm_end = address;
>  				anon_vma_interval_tree_post_update_vma(vma);
> @@ -2281,6 +2280,8 @@ int expand_downwards(struct vm_area_stru
>  				 * against concurrent vma expansions.
>  				 */
>  				spin_lock(&vma->vm_mm->page_table_lock);
> +				if (vma->vm_flags & VM_LOCKED)
> +					mm->locked_vm += grow;
>  				anon_vma_interval_tree_pre_update_vma(vma);
>  				vma->vm_start = address;
>  				vma->vm_pgoff -= grow;

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

Re: Multiple potential races on vma->vm_flags Oleg Nesterov <oleg@redhat.com> - 2015-09-23 17:40 +0200
  Re: Multiple potential races on vma->vm_flags Oleg Nesterov <oleg@redhat.com> - 2015-09-23 17:50 +0200

csiph-web