Re: [PATCH] drm/sched: Fix kernel NULL pointer dereference error

[Michal Kubecek <mkubecek@suse.cz>]

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On Fri, Sep 30, 2022 at 09:09:56PM +0530, Yadav, Arvind wrote:
> 
> On 9/30/2022 4:56 PM, Christian König wrote:
> > Am 30.09.22 um 10:48 schrieb Arvind Yadav:
> > > BUG: kernel NULL pointer dereference, address: 0000000000000088
> > >   #PF: supervisor read access in kernel mode
> > >   #PF: error_code(0x0000) - not-present page
> > >   PGD 0 P4D 0
> > >   Oops: 0000 [#1] PREEMPT SMP NOPTI
> > >   CPU: 2 PID: 0 Comm: swapper/2 Not tainted 6.0.0-rc2-custom #1
> > >   Arvind : [dma_fence_default_wait _START] timeout = -1
> > >   Hardware name: AMD Dibbler/Dibbler, BIOS RDB1107CC 09/26/2018
> > >   RIP: 0010:drm_sched_job_done.isra.0+0x11/0x140 [gpu_sched]
> > >   Code: 8b fe ff ff be 03 00 00 00 e8 7b da b7 e3 e9 d4 fe ff ff 66
> > > 0f 1f 44 00 00 0f 1f 44 00 00 55 48 89 e5 41 55 41 54 49 89 fc 53
> > > <48> 8b 9f 88 00 00 00 f0 ff 8b f0 00 00 00 48 8b 83 80 01 00 00 f0
> > >   RSP: 0018:ffffb1b1801d4d38 EFLAGS: 00010087
> > >   RAX: ffffffffc0aa48b0 RBX: ffffb1b1801d4d70 RCX: 0000000000000018
> > >   RDX: 000036c70afb7c1d RSI: ffff8a45ca413c60 RDI: 0000000000000000
> > >   RBP: ffffb1b1801d4d50 R08: 00000000000000b5 R09: 0000000000000000
> > >   R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> > >   R13: ffffb1b1801d4d70 R14: ffff8a45c4160000 R15: ffff8a45c416a708
> > >   FS:  0000000000000000(0000) GS:ffff8a48a0a80000(0000)
> > > knlGS:0000000000000000
> > >   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > >   CR2: 0000000000000088 CR3: 000000014ad50000 CR4: 00000000003506e0
> > >   Call Trace:
> > >    <IRQ>
> > >    drm_sched_job_done_cb+0x12/0x20 [gpu_sched]
> > >    dma_fence_signal_timestamp_locked+0x7e/0x110
> > >    dma_fence_signal+0x31/0x60
> > >    amdgpu_fence_process+0xc4/0x140 [amdgpu]
> > >    gfx_v9_0_eop_irq+0x9d/0xd0 [amdgpu]
> > >    amdgpu_irq_dispatch+0xb7/0x210 [amdgpu]
> > >    amdgpu_ih_process+0x86/0x100 [amdgpu]
> > >    amdgpu_irq_handler+0x24/0x60 [amdgpu]
> > >    __handle_irq_event_percpu+0x4b/0x190
> > >    handle_irq_event_percpu+0x15/0x50
> > >    handle_irq_event+0x39/0x60
> > >    handle_edge_irq+0xaf/0x210
> > >    __common_interrupt+0x6e/0x110
> > >    common_interrupt+0xc1/0xe0
> > >    </IRQ>
> > >    <TASK>
> > 
> > How is this triggered any why haven't we seen it before?
> 
> IGT has few 'amdgpu' specific testcases which is not related  to fence.
> 
> while running those test cases I have got this crash but this crash is not
> always reproducible.

I've encountered this crash twice (out of two attempts) with kernel
built from mainline commit 4c86114194e6 when I started firefox.

The patch below fixed the crash and does not seem to introduce any
apparent issue.

Tested-by: Michal Kubecek <mkubecek@suse.cz>

> > > Signed-off-by: Arvind Yadav <Arvind.Yadav@amd.com>
> > > ---
> > >   drivers/gpu/drm/scheduler/sched_main.c | 7 ++++++-
> > >   1 file changed, 6 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/scheduler/sched_main.c
> > > b/drivers/gpu/drm/scheduler/sched_main.c
> > > index 6684d88463b4..390272f6b126 100644
> > > --- a/drivers/gpu/drm/scheduler/sched_main.c
> > > +++ b/drivers/gpu/drm/scheduler/sched_main.c
> > > @@ -172,7 +172,12 @@ drm_sched_rq_select_entity(struct drm_sched_rq *rq)
> > >   static void drm_sched_job_done(struct drm_sched_job *s_job)
> > >   {
> > >       struct drm_sched_fence *s_fence = s_job->s_fence;
> > > -    struct drm_gpu_scheduler *sched = s_fence->sched;
> > > +    struct drm_gpu_scheduler *sched;
> > > +
> > > +    if (!s_fence)
> > > +        return;
> > > +
> > > +    sched = s_fence->sched;
> > >         atomic_dec(&sched->hw_rq_count);
> > >       atomic_dec(sched->score);
> > 

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