Re: [PATCH 2/2] aio: make aio .mremap handle size changes

[Benjamin LaHaise <bcrl@kvack.org>]

On Tue, Feb 03, 2015 at 11:18:53AM -0800, Shaohua Li wrote:
> mremap aio ring buffer to another smaller vma is legal. For example,
> mremap the ring buffer from the begining, though after the mremap, some
> ring buffer pages can't be accessed in userspace because vma size is
> shrinked. The problem is ctx->mmap_size isn't changed if the new ring
> buffer vma size is changed. Latter io_destroy will zap all vmas within
> mmap_size, which might zap unrelated vmas.

Nak.  Shrinking the aio ring buffer is not a supported operation and will 
cause the application to lose events.  Make the size changing mremap fail, 
as this patch will not make the system do the right thing.

		-ben

> Cc: Benjamin LaHaise <bcrl@kvack.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Shaohua Li <shli@fb.com>
> ---
>  fs/aio.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/aio.c b/fs/aio.c
> index 1b7893e..fa354cf 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -306,6 +306,7 @@ static void aio_ring_remap(struct file *file, struct vm_area_struct *vma)
>  		ctx = table->table[i];
>  		if (ctx && ctx->aio_ring_file == file) {
>  			ctx->user_id = ctx->mmap_base = vma->vm_start;
> +			ctx->mmap_size = vma->vm_end - vma->vm_start;
>  			break;
>  		}
>  	}
> -- 
> 1.8.1

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