Re: [PATCH 2/2] adreno: Detect shutdown during get_param()

[Joel Fernandes]

On Sat, Nov 12, 2022 at 6:35 PM Rob Clark <robdclark@xxxxxxxxx> wrote:
>
> On Fri, Nov 11, 2022 at 1:28 PM Akhil P Oommen <quic_akhilpo@xxxxxxxxxxx> wrote:
> >
> > On 11/12/2022 1:19 AM, Joel Fernandes (Google) wrote:
> > > Even though the GPU is shut down, during kexec reboot we can have userspace
> > > still running. This is especially true if KEXEC_JUMP is not enabled, because we
> > > do not freeze userspace in this case.
> > >
> > > To prevent crashes, track that the GPU is shutdown and prevent get_param() from
> > > accessing GPU resources if we find it shutdown.
> > >
> > > This fixes the following crash during kexec reboot on an ARM64 device with adreno GPU:
> > >
> > > [  292.534314] Kernel panic - not syncing: Asynchronous SError Interrupt
> > > [  292.534323] Hardware name: Google Lazor (rev3 - 8) with LTE (DT)
> > > [  292.534326] Call trace:
> > > [  292.534328]  dump_backtrace+0x0/0x1d4
> > > [  292.534337]  show_stack+0x20/0x2c
> > > [  292.534342]  dump_stack_lvl+0x60/0x78
> > > [  292.534347]  dump_stack+0x18/0x38
> > > [  292.534352]  panic+0x148/0x3b0
> > > [  292.534357]  nmi_panic+0x80/0x94
> > > [  292.534364]  arm64_serror_panic+0x70/0x7c
> > > [  292.534369]  do_serror+0x0/0x7c
> > > [  292.534372]  do_serror+0x54/0x7c
> > > [  292.534377]  el1h_64_error_handler+0x34/0x4c
> > > [  292.534381]  el1h_64_error+0x7c/0x80
> > > [  292.534386]  el1_interrupt+0x20/0x58
> > > [  292.534389]  el1h_64_irq_handler+0x18/0x24
> > > [  292.534395]  el1h_64_irq+0x7c/0x80
> > > [  292.534399]  local_daif_inherit+0x10/0x18
> > > [  292.534405]  el1h_64_sync_handler+0x48/0xb4
> > > [  292.534410]  el1h_64_sync+0x7c/0x80
> > > [  292.534414]  a6xx_gmu_set_oob+0xbc/0x1fc
> > > [  292.534422]  a6xx_get_timestamp+0x40/0xb4
> > > [  292.534426]  adreno_get_param+0x12c/0x1e0
> > > [  292.534433]  msm_ioctl_get_param+0x64/0x70
> > > [  292.534440]  drm_ioctl_kernel+0xe8/0x158
> > > [  292.534448]  drm_ioctl+0x208/0x320
> > > [  292.534453]  __arm64_sys_ioctl+0x98/0xd0
> > > [  292.534461]  invoke_syscall+0x4c/0x118
> > > [  292.534467]  el0_svc_common+0x98/0x104
> > > [  292.534473]  do_el0_svc+0x30/0x80
> > > [  292.534478]  el0_svc+0x20/0x50
> > > [  292.534481]  el0t_64_sync_handler+0x78/0x108
> > > [  292.534485]  el0t_64_sync+0x1a4/0x1a8
> > > [  292.534632] Kernel Offset: 0x1a5f800000 from 0xffffffc008000000
> > > [  292.534635] PHYS_OFFSET: 0x80000000
> > > [  292.534638] CPU features: 0x40018541,a3300e42
> > > [  292.534644] Memory Limit: none
> > >
> > > Cc: Rob Clark <robdclark@xxxxxxxxxxxx>
> > > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > > Cc: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> > > Cc: Ross Zwisler <zwisler@xxxxxxxxxx>
> > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> > > ---
> > >   drivers/gpu/drm/msm/adreno/adreno_device.c | 1 +
> > >   drivers/gpu/drm/msm/adreno/adreno_gpu.c    | 2 +-
> > >   drivers/gpu/drm/msm/msm_gpu.h              | 3 +++
> > >   3 files changed, 5 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/msm/adreno/adreno_device.c b/drivers/gpu/drm/msm/adreno/adreno_device.c
> > > index f0cff62812c3..03d912dc0130 100644
> > > --- a/drivers/gpu/drm/msm/adreno/adreno_device.c
> > > +++ b/drivers/gpu/drm/msm/adreno/adreno_device.c
> > > @@ -612,6 +612,7 @@ static void adreno_shutdown(struct platform_device *pdev)
> > >   {
> > >       struct msm_gpu *gpu = dev_to_gpu(&pdev->dev);
> > >
> > > +     gpu->is_shutdown = true;
> > >       WARN_ON_ONCE(adreno_system_suspend(&pdev->dev));
> > >   }
> > >
> > > diff --git a/drivers/gpu/drm/msm/adreno/adreno_gpu.c b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> > > index 382fb7f9e497..6903c6892469 100644
> > > --- a/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> > > +++ b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> > > @@ -251,7 +251,7 @@ int adreno_get_param(struct msm_gpu *gpu, struct msm_file_private *ctx,
> > >       struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > >
> > >       /* No pointer params yet */
> > > -     if (*len != 0)
> > > +     if (*len != 0 || gpu->is_shutdown)
> > >               return -EINVAL;
> > This will race with shutdown. Probably, propagating back the return
> > value of pm_runtime_get() in every possible ioctl call path is the right
> > thing to do.
> >
> > I have never thought about this scenario. Do you know why userspace is
> > not freezed before kexec?
>
> So userspace not being frozen seems like the root issue, and is likely
> to cause all sorts of other whack-a-mole problems.  I guess I'd like
> to know if this is the expected behavior?

We tried that. Freezing before kexec seems to cause issues for ALSA as
Ricardo found:
https://lore.kernel.org/lkml/202211281209.mnBLzQ2I-lkp@xxxxxxxxx/T/

That patch is still TBD due to disagreement on the right approach to
fix, so I don't think freezing before shutting down devices is viable
at the moment.

I am checking Ricardo if we can do something like util-linux's
shutdown code which sends SIGTERM to all processes:
https://kernel.googlesource.com/pub/scm/utils/util-linux/util-linux/+/v2.8/login-utils/shutdown.c#273
, before issuing the kexec-reboot.

Maybe, a more graceful shutdown from kexec-lite, will prevent the
kexec-reboot it does from crashing? Though in my view that would still
be a small copout instead of fixing the real issue, which is the
kernel crashing for any reason.

> If so, we should probably look at
> drm_dev_is_unplugged()/drm_dev_unplug()/etc rather than trying to NIH
> that mechanism.  We would need to sprinkle drm_dev_is_unplugged()
> checks more widely, and also ensure that the scheduler kthread(s) gets
> parked.  But it would be nice to know first if we are just trying to
> paper over a kexec bug.

Agreed. I think we still patch 1/2 whether the SIGTERM trick mentioned
above, works or not. I will await discussions with Ricardo before
reposting that one.

Cheers,

 -- Joel