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Date: Fri, 25 Feb 2011 11:49:21 -0300
From: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
To: Anca Emanuel <anca.emanuel@gmail.com>
Cc: Dave Airlie <airlied@redhat.com>,
        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>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andy Whitcroft <apw@canonical.com>
Subject: Re: Linux 2.6.38-rc6
Message-ID: <20110225144920.GA2337@herton-IdeaPad-Y430>
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On Fri, Feb 25, 2011 at 03:56:20AM +0200, Anca Emanuel wrote:
> On Fri, Feb 25, 2011 at 3:47 AM, Anca Emanuel <anca.emanuel@gmail.com> wrote:
> > 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>
> >
> 
> link to patch: http://is.gd/otIfGc

Adding Andy on CC (btw he is away for today, may get some time to answer).

Andy, can you repost the patch?

--
[]'s
Herton
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