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Date: Fri, 25 Feb 2011 03:47:58 +0200
Message-ID: <AANLkTikQOBGfe8dGv05M8YD=CK+ToUQ4J8s_n9FncfPA@mail.gmail.com>
Subject: Re: Linux 2.6.38-rc6
From: Anca Emanuel <anca.emanuel@gmail.com>
To: Dave Airlie <airlied@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        linux-fbdev@vger.kernel.org, Ben Skeggs <bskeggs@redhat.com>,
        dri-devel@lists.freedesktop.org, Borislav Petkov <bp@amd64.org>,
        Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Fri, Feb 25, 2011 at 3:14 AM, Dave Airlie <airlied@redhat.com> wrote:
> On Thu, 2011-02-24 at 16:54 -0800, Linus Torvalds wrote:
>> 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?
>
> I think Andy's patch worked, not sure why it fell between the cracks,
> either didn't appear on lkml or in my inbox at all.
>
> if we can get Herton to repost it properly + a tested by I'm happy for
> it to go in.
>
> Dave.
>
>

Tested Andy's patch and it works !
http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-natty.git;a=commit;h=c5a742b5f78e161d6a13853a7e3e6e1dfa429e69

Tested-by: Anca Emanuel <anca.emanuel@gmail.com>
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