RE: [PATCH 2/3] drm/amdgpu: fix the fence timeline null pointer

["Huang, Ray" <Ray.Huang@amd.com>]

[AMD Official Use Only]

> -----Original Message-----
> From: Koenig, Christian <Christian.Koenig@amd.com>
> Sent: Tuesday, December 14, 2021 4:01 PM
> To: Huang, Ray <Ray.Huang@amd.com>; dri-devel@lists.freedesktop.org;
> Daniel Vetter <daniel.vetter@ffwll.ch>; Sumit Semwal
> <sumit.semwal@linaro.org>
> Cc: amd-gfx@lists.freedesktop.org; linux-media@vger.kernel.org; Deucher,
> Alexander <Alexander.Deucher@amd.com>; Liu, Monk
> <Monk.Liu@amd.com>
> Subject: Re: [PATCH 2/3] drm/amdgpu: fix the fence timeline null pointer
> 
> Am 13.12.21 um 07:34 schrieb Huang Rui:
> > Initialize the flags for embedded fence in the job at dma_fence_init().
> > Otherwise, we will go a wrong way in amdgpu_fence_get_timeline_name
> > callback and trigger a null pointer panic once we enabled the trace
> > event here.
> >
> > [  156.131790] BUG: kernel NULL pointer dereference, address:
> > 00000000000002a0 [  156.131804] #PF: supervisor read access in kernel
> > mode [  156.131811] #PF: error_code(0x0000) - not-present page [
> > 156.131817] PGD 0 P4D 0 [  156.131824] Oops: 0000 [#1] PREEMPT SMP PTI
> > [  156.131832] CPU: 6 PID: 1404 Comm: sdma0 Tainted: G           OE     5.16.0-
> rc1-custom #1
> > [  156.131842] Hardware name: Gigabyte Technology Co., Ltd.
> > Z170XP-SLI/Z170XP-SLI-CF, BIOS F20 11/04/2016 [  156.131848] RIP:
> > 0010:strlen+0x0/0x20 [  156.131859] Code: 89 c0 c3 0f 1f 80 00 00 00
> > 00 48 01 fe eb 0f 0f b6 07 38 d0 74 10 48 83 c7 01 84 c0 74 05 48 39
> > f7 75 ec 31 c0 c3 48 89 f8 c3 <80> 3f 00 74 10 48 89 f8 48 83 c0 01 80
> > 38 00 75 f7 48 29 f8 c3 31 [  156.131872] RSP: 0018:ffff9bd0018dbcf8
> > EFLAGS: 00010206 [  156.131880] RAX: 00000000000002a0 RBX:
> > ffff8d0305ef01b0 RCX: 000000000000000b [  156.131888] RDX:
> > ffff8d03772ab924 RSI: ffff8d0305ef01b0 RDI: 00000000000002a0 [
> > 156.131895] RBP: ffff9bd0018dbd60 R08: ffff8d03002094d0 R09:
> > 0000000000000000 [  156.131901] R10: 000000000000005e R11:
> > 0000000000000065 R12: ffff8d03002094d0 [  156.131907] R13:
> > 000000000000001f R14: 0000000000070018 R15: 0000000000000007 [
> > 156.131914] FS:  0000000000000000(0000) GS:ffff8d062ed80000(0000)
> > knlGS:0000000000000000 [  156.131923] CS:  0010 DS: 0000 ES: 0000 CR0:
> 0000000080050033 [  156.131929] CR2: 00000000000002a0 CR3:
> 000000001120a005 CR4: 00000000003706e0 [  156.131937] DR0:
> 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [  156.131942] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
> 0000000000000400 [  156.131949] Call Trace:
> > [  156.131953]  <TASK>
> > [  156.131957]  ? trace_event_raw_event_dma_fence+0xcc/0x200
> > [  156.131973]  ? ring_buffer_unlock_commit+0x23/0x130
> > [  156.131982]  dma_fence_init+0x92/0xb0 [  156.131993]
> > amdgpu_fence_emit+0x10d/0x2b0 [amdgpu] [  156.132302]
> > amdgpu_ib_schedule+0x2f9/0x580 [amdgpu] [  156.132586]
> > amdgpu_job_run+0xed/0x220 [amdgpu]
> >
> > Signed-off-by: Huang Rui <ray.huang@amd.com>
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c | 17 +++++++++--------
> >   1 file changed, 9 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
> > index 3b7e86ea7167..e2aa71904278 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
> > @@ -76,7 +76,7 @@ void amdgpu_fence_slab_fini(void)
> >   /*
> >    * Cast helper
> >    */
> > -static const struct dma_fence_ops amdgpu_fence_ops;
> > +static struct dma_fence_ops amdgpu_fence_ops;
> >   static inline struct amdgpu_fence *to_amdgpu_fence(struct dma_fence
> *f)
> >   {
> >   	struct amdgpu_fence *__f = container_of(f, struct amdgpu_fence,
> > base); @@ -158,21 +158,22 @@ int amdgpu_fence_emit(struct
> amdgpu_ring *ring, struct dma_fence **f, struct amd
> >   	}
> >
> >   	seq = ++ring->fence_drv.sync_seq;
> > -	if (job != NULL && job->job_run_counter) {
> > +	if (job && job->job_run_counter) {
> >   		/* reinit seq for resubmitted jobs */
> >   		fence->seqno = seq;
> > +		set_bit(AMDGPU_FENCE_FLAG_EMBED_IN_JOB_BIT,
> &fence->flags);
> >   	} else {
> > +		amdgpu_fence_ops.init_flags = 0;
> > +		if (job)
> > +			set_bit(AMDGPU_FENCE_FLAG_EMBED_IN_JOB_BIT,
> > +				&amdgpu_fence_ops.init_flags);
> 
> That is utterly nonsense. The amdgpu_fence_ops are global and can't be
> modified like that.
> 

Please check the reply in patch1, we need initialize the fence and assign the flags together, otherwise it will trigger the panic once the trace event is enabled.

Thanks,
Ray

> Christian.
> 
> > +
> >   		dma_fence_init(fence, &amdgpu_fence_ops,
> >   				&ring->fence_drv.lock,
> >   				adev->fence_context + ring->idx,
> >   				seq);
> >   	}
> >
> > -	if (job != NULL) {
> > -		/* mark this fence has a parent job */
> > -		set_bit(AMDGPU_FENCE_FLAG_EMBED_IN_JOB_BIT,
> &fence->flags);
> > -	}
> > -
> >   	amdgpu_ring_emit_fence(ring, ring->fence_drv.gpu_addr,
> >   			       seq, flags | AMDGPU_FENCE_FLAG_INT);
> >   	pm_runtime_get_noresume(adev_to_drm(adev)->dev);
> > @@ -720,7 +721,7 @@ static void amdgpu_fence_release(struct
> dma_fence *f)
> >   	call_rcu(&f->rcu, amdgpu_fence_free);
> >   }
> >
> > -static const struct dma_fence_ops amdgpu_fence_ops = {
> > +static struct dma_fence_ops amdgpu_fence_ops = {
> >   	.get_driver_name = amdgpu_fence_get_driver_name,
> >   	.get_timeline_name = amdgpu_fence_get_timeline_name,
> >   	.enable_signaling = amdgpu_fence_enable_signaling,