Re: [PATCH] drm/buddy: Fix alloc_range() error handling code

[Daniel Vetter <daniel@ffwll.ch>]

On Sat, Feb 10, 2024 at 12:06:58AM +0530, Arunpravin Paneer Selvam wrote:
> Hi Daniel,
> 
> On 2/9/2024 11:34 PM, Daniel Vetter wrote:
> > On Fri, Feb 09, 2024 at 08:56:24PM +0530, Arunpravin Paneer Selvam wrote:
> > > Few users have observed display corruption when they boot
> > > the machine to KDE Plasma or playing games. We have root
> > > caused the problem that whenever alloc_range() couldn't
> > > find the required memory blocks the function was returning
> > > SUCCESS in some of the corner cases.
> > > 
> > > The right approach would be if the total allocated size
> > > is less than the required size, the function should
> > > return -ENOSPC.
> > > 
> > > Cc:  <stable@vger.kernel.org> # 6.7+
> > > Fixes: 0a1844bf0b53 ("drm/buddy: Improve contiguous memory allocation")
> > > Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3097
> > > Tested-by: Mario Limonciello <mario.limonciello@amd.com>
> > > Link: https://patchwork.kernel.org/project/dri-devel/patch/20240207174456.341121-1-Arunpravin.PaneerSelvam@amd.com/
> > > Acked-by: Christian König <christian.koenig@amd.com>
> > > Reviewed-by: Matthew Auld <matthew.auld@intel.com>
> > > Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
> > New unit test for this would be most excellent - these kind of missed edge
> > cases is exactly what kunit is for. Can you please follow up with, since
> > we don't want to hold up the bugfix for longer?
> Matthew Auld has added a new unit test for this case. Please let us know if
> this will suffice.
> https://patchwork.freedesktop.org/patch/577497/?series=129671&rev=1

Ah yeah, might be best to submit them both together as one series (you
just need to add your own signed-off-by if you resend other people's
patches). That way bots can pick it up together, since new testcase and
bugfix only make sense together.
-Sima

> 
> Thanks,
> Arun.
> > -Sima
> > 
> > > ---
> > >   drivers/gpu/drm/drm_buddy.c | 6 ++++++
> > >   1 file changed, 6 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
> > > index f57e6d74fb0e..c1a99bf4dffd 100644
> > > --- a/drivers/gpu/drm/drm_buddy.c
> > > +++ b/drivers/gpu/drm/drm_buddy.c
> > > @@ -539,6 +539,12 @@ static int __alloc_range(struct drm_buddy *mm,
> > >   	} while (1);
> > >   	list_splice_tail(&allocated, blocks);
> > > +
> > > +	if (total_allocated < size) {
> > > +		err = -ENOSPC;
> > > +		goto err_free;
> > > +	}
> > > +
> > >   	return 0;
> > >   err_undo:
> > > -- 
> > > 2.25.1
> > > 
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch