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Re: [PATCH] drm/gma500: fix double freeing

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  Re: [PATCH] drm/gma500: fix double freeing Sudip Mukherjee <sudipm.mukherjee@gmail.com> - 2015-09-24 18:00 +0200
    Re: [PATCH] drm/gma500: fix double freeing Patrik Jakobsson <patrik.r.jakobsson@gmail.com> - 2015-09-29 15:30 +0200
      Re: [PATCH] drm/gma500: fix double freeing Sudip Mukherjee <sudipm.mukherjee@gmail.com> - 2015-09-30 08:20 +0200
        Re: [PATCH] drm/gma500: fix double freeing Patrik Jakobsson <patrik.r.jakobsson@gmail.com> - 2015-10-01 19:10 +0200
          Re: [PATCH] drm/gma500: fix double freeing Sudip Mukherjee <sudipm.mukherjee@gmail.com> - 2015-10-02 18:00 +0200

#1232218 — Re: [PATCH] drm/gma500: fix double freeing

On Wed, Sep 09, 2015 at 06:20:40PM +0530, Sudip Mukherjee wrote:
> If backing->stolen is true then we were freeing backing by calling
> psb_gtt_free_range() but we called it again after unlocking the mutex.
> Lets make it NULL after freeing in psb_gtt_free_range() and check for
> NULL before calling the function for the second time.
> 
> Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
> ---
Hi Patrik,
A gentle ping.

regards
sudip
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#1235052

On Thu, Sep 24, 2015 at 5:57 PM, Sudip Mukherjee
<sudipm.mukherjee@gmail.com> wrote:
> On Wed, Sep 09, 2015 at 06:20:40PM +0530, Sudip Mukherjee wrote:
>> If backing->stolen is true then we were freeing backing by calling
>> psb_gtt_free_range() but we called it again after unlocking the mutex.
>> Lets make it NULL after freeing in psb_gtt_free_range() and check for
>> NULL before calling the function for the second time.
>>
>> Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
>> ---
> Hi Patrik,
> A gentle ping.
>
> regards
> sudip

Hi, sorry for the late reply.

Why are we freeing the range twice in the first case?

-Patrik
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#1235792

On Tue, Sep 29, 2015 at 03:20:35PM +0200, Patrik Jakobsson wrote:
> On Thu, Sep 24, 2015 at 5:57 PM, Sudip Mukherjee
> <sudipm.mukherjee@gmail.com> wrote:
> > On Wed, Sep 09, 2015 at 06:20:40PM +0530, Sudip Mukherjee wrote:
> >> If backing->stolen is true then we were freeing backing by calling
> >> psb_gtt_free_range() but we called it again after unlocking the mutex.
> >> Lets make it NULL after freeing in psb_gtt_free_range() and check for
> >> NULL before calling the function for the second time.
> >>
> >> Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
> >> ---
> > Hi Patrik,
> > A gentle ping.
> >
> > regards
> > sudip
> 
> Hi, sorry for the late reply.
> 
> Why are we freeing the range twice in the first case?
I think,
if backing->stolen is true then backing is released using
psb_gtt_free_range() but if backing->stolen is false then the gem object
is freed but the backing is not yet freed. To free that backing
psb_gtt_free_range() has been called second time. My patch tried to fix
the possibility of backing->stolen being true and backing being freed 2
times.

regards
sudip

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#1237574

On Wed, Sep 30, 2015 at 8:12 AM, Sudip Mukherjee
<sudipm.mukherjee@gmail.com> wrote:
> On Tue, Sep 29, 2015 at 03:20:35PM +0200, Patrik Jakobsson wrote:
>> On Thu, Sep 24, 2015 at 5:57 PM, Sudip Mukherjee
>> <sudipm.mukherjee@gmail.com> wrote:
>> > On Wed, Sep 09, 2015 at 06:20:40PM +0530, Sudip Mukherjee wrote:
>> >> If backing->stolen is true then we were freeing backing by calling
>> >> psb_gtt_free_range() but we called it again after unlocking the mutex.
>> >> Lets make it NULL after freeing in psb_gtt_free_range() and check for
>> >> NULL before calling the function for the second time.
>> >>
>> >> Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
>> >> ---
>> > Hi Patrik,
>> > A gentle ping.
>> >
>> > regards
>> > sudip
>>
>> Hi, sorry for the late reply.
>>
>> Why are we freeing the range twice in the first case?
> I think,
> if backing->stolen is true then backing is released using
> psb_gtt_free_range() but if backing->stolen is false then the gem object
> is freed but the backing is not yet freed. To free that backing
> psb_gtt_free_range() has been called second time. My patch tried to fix
> the possibility of backing->stolen being true and backing being freed 2
> times.
>
> regards
> sudip

There are some special handling of the stolen framebuffer that I don't
remember entirely but the basic concept is that we free the backing
when we drop the last reference on a gem object. That will trigger a
psb_gtt_free_range(). So in this case it looks to me that the extra
free is not needed at all. That's my quick reasoning, feel free to
prove me wrong :)

Thanks
Patrik
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#1238378

On Thu, Oct 01, 2015 at 07:07:33PM +0200, Patrik Jakobsson wrote:
> On Wed, Sep 30, 2015 at 8:12 AM, Sudip Mukherjee
> <sudipm.mukherjee@gmail.com> wrote:
> > On Tue, Sep 29, 2015 at 03:20:35PM +0200, Patrik Jakobsson wrote:
> >> On Thu, Sep 24, 2015 at 5:57 PM, Sudip Mukherjee
> >> <sudipm.mukherjee@gmail.com> wrote:
> >> > On Wed, Sep 09, 2015 at 06:20:40PM +0530, Sudip Mukherjee wrote:
> >> >> If backing->stolen is true then we were freeing backing by calling
> >> >> psb_gtt_free_range() but we called it again after unlocking the mutex.
> >> >> Lets make it NULL after freeing in psb_gtt_free_range() and check for
> >> >> NULL before calling the function for the second time.
> >> >>
> >> >> Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
> >> >> ---
> >> > Hi Patrik,
> >> > A gentle ping.
> >> >
> >> > regards
> >> > sudip
> >>
> >> Hi, sorry for the late reply.
> >>
> >> Why are we freeing the range twice in the first case?
> > I think,
> > if backing->stolen is true then backing is released using
> > psb_gtt_free_range() but if backing->stolen is false then the gem object
> > is freed but the backing is not yet freed. To free that backing
> > psb_gtt_free_range() has been called second time. My patch tried to fix
> > the possibility of backing->stolen being true and backing being freed 2
> > times.
> >
> > regards
> > sudip
> 
> There are some special handling of the stolen framebuffer that I don't
> remember entirely but the basic concept is that we free the backing
> when we drop the last reference on a gem object. That will trigger a
> psb_gtt_free_range(). So in this case it looks to me that the extra
> free is not needed at all. That's my quick reasoning, feel free to
> prove me wrong :)

In this case we are allocating backing using psbfb_alloc() and so
backing->stolen is always true. So we can remove the backing->stolen
condition. And if drm_fb_helper_alloc_fbi() fails then we
are jumping to out_err1. So the fitst free will not be needed.

diff --git a/drivers/gpu/drm/gma500/framebuffer.c b/drivers/gpu/drm/gma500/framebuffer.c
index 2eaf1b3..932f07b 100644
--- a/drivers/gpu/drm/gma500/framebuffer.c
+++ b/drivers/gpu/drm/gma500/framebuffer.c
@@ -466,11 +466,6 @@ static int psbfb_create(struct psb_fbdev *fbdev,
 	mutex_unlock(&dev->struct_mutex);
 	return 0;
 out_unref:
-	if (backing->stolen)
-		psb_gtt_free_range(dev, backing);
-	else
-		drm_gem_object_unreference(&backing->gem);
-
 	drm_fb_helper_release_fbi(&fbdev->psb_fb_helper);
 out_err1:
 	mutex_unlock(&dev->struct_mutex);


If it is ok, I can submit the v2.

regards
sudip
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