Re: [Linux-fbdev-devel] Re: [PATCH?] Crash in 2.4.17/ptrace

[James Simmons]

> Ah, thanks.  Also I missed sbusfb.c (not that it was fatal - the driver
> got it right anyway).

Great.
 
> Here's the current patch.  After some discussion with Ben
> Herrenschmidt, it now sets VM_IO against the vma *before*
> calling the subdriver's mmap method, just in case the
> driver really does want to clear that flag (presumably, a shadow
> buffer in main memory).

I also thought about it as well. Never thought about the issue with shadow
buffers. Is it safe to move it before if (fb->fb_mmap)? 

> --- linux-2.4.18-pre7/drivers/video/fbmem.c	Fri Dec 21 11:19:14 2001
> +++ linux-akpm/drivers/video/fbmem.c	Tue Jan 29 14:57:00 2002
> @@ -541,6 +541,16 @@ fb_mmap(struct file *file, struct vm_are
>  	if (fb->fb_mmap) {
>  		int res;
>  		lock_kernel();
> +		/*
> +		 * This is an IO map - tell maydump to skip this VMA.
> +		 * If, for some reason, the sub-driver wishes to allow the
> +		 * mapping to be dumpable and accessible via ptrace then
> +		 * it may clear VM_IO later.
> +		 * (This only makes sense if the buffer is actually
> +		 * in main memory, and is described by a page struct in
> +		 * mem_map[])
> +		 */
> +		vma->vm_flags |= VM_IO;
>  		res = fb->fb_mmap(info, file, vma);
>  		unlock_kernel();
>  		return res;