linux-kernel - Re: [PATCH AUTOSEL 5.10 13/22] drm/amdgpu: install stub fence into potential unused fence pointers

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Message-ID: <CAPaKu7Q2vq5m6Av6L2LthnFy5w2XtjKUYF8Z2__0hVp0vj2L1A@mail.gmail.com>
Date:   Thu, 31 Aug 2023 11:55:53 -0700
From:   Chia-I Wu <olvaffe@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Christian König <ckoenig.leichtzumerken@...il.com>,
        Sasha Levin <sashal@...nel.org>, airlied@...ux.ie,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        amd-gfx@...ts.freedesktop.org,
        Alex Deucher <alexander.deucher@....com>,
        stable@...r.kernel.org, Lang Yu <Lang.Yu@....com>,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH AUTOSEL 5.10 13/22] drm/amdgpu: install stub fence into
 potential unused fence pointers

On Thu, Aug 31, 2023 at 7:01 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Thu, Aug 31, 2023 at 03:26:28PM +0200, Christian König wrote:
> > Am 31.08.23 um 12:56 schrieb Greg KH:
> > > On Thu, Aug 31, 2023 at 12:27:27PM +0200, Christian König wrote:
> > > > Am 30.08.23 um 20:53 schrieb Chia-I Wu:
> > > > > On Sun, Jul 23, 2023 at 6:24 PM Sasha Levin <sashal@...nel.org> wrote:
> > > > > > From: Lang Yu <Lang.Yu@....com>
> > > > > >
> > > > > > [ Upstream commit 187916e6ed9d0c3b3abc27429f7a5f8c936bd1f0 ]
> > > > > >
> > > > > > When using cpu to update page tables, vm update fences are unused.
> > > > > > Install stub fence into these fence pointers instead of NULL
> > > > > > to avoid NULL dereference when calling dma_fence_wait() on them.
> > > > > >
> > > > > > Suggested-by: Christian König <christian.koenig@....com>
> > > > > > Signed-off-by: Lang Yu <Lang.Yu@....com>
> > > > > > Reviewed-by: Christian König <christian.koenig@....com>
> > > > > > Signed-off-by: Alex Deucher <alexander.deucher@....com>
> > > > > > Signed-off-by: Sasha Levin <sashal@...nel.org>
> > > > > > ---
> > > > > >    drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 6 ++++--
> > > > > >    1 file changed, 4 insertions(+), 2 deletions(-)
> > > > > We start getting this warning spew on chromeos
> > > > Yeah because the older kernels still kept track of the last VM fence in the
> > > > syncobj.
> > > >
> > > > This patch here should probably not have been back ported.
> > > >
> > > > Why was that done anyway? The upstream commit doesn't have a CC stable and
> > > > this is only a bug fix for a new feature not present on older kernels.
> > > It is part of the AUTOSEL process.
> >
> > Could we prevent patches from being backported by adding a Fixes: tag?
>
> Yes, that will show exactly where the patch should be backported to.
This is also AUTOSEL'ed to 5.15.  That might need a revert as well,
depending on when the amdgpu feature landed.


>
> thanks,
>
> greg k-h