Re: Linux 2.6.38-rc6

[Linus Torvalds <torvalds@linux-foundation.org>]

On Thu, Feb 24, 2011 at 4:48 PM, Anca Emanuel <anca.emanuel@gmail.com> wrote:
>
> diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
> index e2bf953..e8f8925 100644
> --- a/drivers/video/fbmem.c
> +++ b/drivers/video/fbmem.c
> @@ -1511,6 +1511,7 @@ void remove_conflicting_framebuffers(struct
> apertures_struct *a,
>                               "%s vs %s - removing generic driver\n",
>                               name, registered_fb[i]->fix.id);
>                        unregister_framebuffer(registered_fb[i]);
> +                       registered_fb[i] = NULL;
>
> Tested the patch, and now I get this:
> dmesg: http://pastebin.com/ieMNrA7C
>
> [   12.252328] BUG: unable to handle kernel NULL pointer dereference
> at 00000000000003b8
> [   12.252342] IP: [<ffffffff81311178>] fb_mmap+0x58/0x1d0

Ok, goodie.

Or not so goodie, but it does make it clear that yeah, the fb code
seems to be using stale pointers from that registered_fb[] array, and
the whole unregistration process is just racing with people using it.

Herton had that much bigger patch, can you test it?

                         Linus