Re: [PATCH] drm/radeon: add a force flush to delay work when radeon

[Christian König]

Am 17.08.22 um 09:31 schrieb 李真能:
> 在 2022/8/15 21:12, Christian König 写道:
> > Am 15.08.22 um 09:34 schrieb 李真能:
> > > 在 2022/8/12 18:55, Christian König 写道:
> > > > Am 11.08.22 um 09:25 schrieb Zhenneng Li:
> > > > > Although radeon card fence and wait for gpu to finish processing 
> > > > > current batch rings,
> > > > > there is still a corner case that radeon lockup work queue may not 
> > > > > be fully flushed,
> > > > > and meanwhile the radeon_suspend_kms() function has called 
> > > > > pci_set_power_state() to
> > > > > put device in D3hot state.
> > > >
> > > > If I'm not completely mistaken the reset worker uses the 
> > > > suspend/resume functionality as well to get the hardware into a 
> > > > working state again.
> > > >
> > > > So if I'm not completely mistaken this here would lead to a 
> > > > deadlock, please double check that.
> > >
> > > We have tested many times, there are no deadlock.
> >
> > Testing doesn't tells you anything, you need to audit the call paths.
> >
> > > In which situation, there would lead to a deadlock?
> >
> > GPU resets.
>
> Although flush_delayed_work(&rdev->fence_drv[i].lockup_work) will wait 
> for a lockup_work to finish executing the last queueing,  but this 
> kernel func haven't get any lock, and lockup_work will run in another 
> kernel thread, so I think flush_delayed_work could not lead to a 
> deadlock.
>
> Therefor if radeon_gpu_reset is called in another thread when 
> radeon_suspend_kms is blocked on flush_delayed_work, there could not 
> lead to a deadlock.

Ok sounds like you didn't go what I wanted to say.

The key problem is that radeon_gpu_reset() calls radeon_suspend() which 
in turn calls rdev->asic->suspend().

And this function in turn could end up in radeon_suspend_kms() again, 
but I'm not 100% sure about that.

Just double check the order of function called here (e.g. if 
radeon_suspend_kms() call radeon_suspend() or the other way around).  
Apart from that your patch looks correct to me as well.

Regards,
Christian.

> > Regards,
> > Christian.
> >
> > > > Regards,
> > > > Christian.
> > > >
> > > > > Per PCI spec rev 4.0 on 5.3.1.4.1 D3hot State.
> > > > > > Configuration and Message requests are the only TLPs accepted by 
> > > > > > a Function in
> > > > > > the D3hot state. All other received Requests must be handled as 
> > > > > > Unsupported Requests,
> > > > > > and all received Completions may optionally be handled as 
> > > > > > Unexpected Completions.
> > > > > This issue will happen in following logs:
> > > > > Unable to handle kernel paging request at virtual address 
> > > > > 00008800e0008010
> > > > > CPU 0 kworker/0:3(131): Oops 0
> > > > > pc = [<ffffffff811bea5c>]  ra = [<ffffffff81240844>]  ps = 0000 
> > > > > Tainted: G        W
> > > > > pc is at si_gpu_check_soft_reset+0x3c/0x240
> > > > > ra is at si_dma_is_lockup+0x34/0xd0
> > > > > v0 = 0000000000000000  t0 = fff08800e0008010  t1 = 0000000000010000
> > > > > t2 = 0000000000008010  t3 = fff00007e3c00000  t4 = fff00007e3c00258
> > > > > t5 = 000000000000ffff  t6 = 0000000000000001  t7 = fff00007ef078000
> > > > > s0 = fff00007e3c016e8  s1 = fff00007e3c00000  s2 = fff00007e3c00018
> > > > > s3 = fff00007e3c00000  s4 = fff00007fff59d80  s5 = 0000000000000000
> > > > > s6 = fff00007ef07bd98
> > > > > a0 = fff00007e3c00000  a1 = fff00007e3c016e8  a2 = 0000000000000008
> > > > > a3 = 0000000000000001  a4 = 8f5c28f5c28f5c29  a5 = ffffffff810f4338
> > > > > t8 = 0000000000000275  t9 = ffffffff809b66f8  t10 = ff6769c5d964b800
> > > > > t11= 000000000000b886  pv = ffffffff811bea20  at = 0000000000000000
> > > > > gp = ffffffff81d89690  sp = 00000000aa814126
> > > > > Disabling lock debugging due to kernel taint
> > > > > Trace:
> > > > > [<ffffffff81240844>] si_dma_is_lockup+0x34/0xd0
> > > > > [<ffffffff81119610>] radeon_fence_check_lockup+0xd0/0x290
> > > > > [<ffffffff80977010>] process_one_work+0x280/0x550
> > > > > [<ffffffff80977350>] worker_thread+0x70/0x7c0
> > > > > [<ffffffff80977410>] worker_thread+0x130/0x7c0
> > > > > [<ffffffff80982040>] kthread+0x200/0x210
> > > > > [<ffffffff809772e0>] worker_thread+0x0/0x7c0
> > > > > [<ffffffff80981f8c>] kthread+0x14c/0x210
> > > > > [<ffffffff80911658>] ret_from_kernel_thread+0x18/0x20
> > > > > [<ffffffff80981e40>] kthread+0x0/0x210
> > > > >   Code: ad3e0008  43f0074a  ad7e0018  ad9e0020  8c3001e8 40230101
> > > > >   <88210000> 4821ed21
> > > > > So force lockup work queue flush to fix this problem.
> > > > >
> > > > > Signed-off-by: Zhenneng Li <lizhenneng@xxxxxxxxxx>
> > > > > ---
> > > > >   drivers/gpu/drm/radeon/radeon_device.c | 3 +++
> > > > >   1 file changed, 3 insertions(+)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/radeon/radeon_device.c 
> > > > > b/drivers/gpu/drm/radeon/radeon_device.c
> > > > > index 15692cb241fc..e608ca26780a 100644
> > > > > --- a/drivers/gpu/drm/radeon/radeon_device.c
> > > > > +++ b/drivers/gpu/drm/radeon/radeon_device.c
> > > > > @@ -1604,6 +1604,9 @@ int radeon_suspend_kms(struct drm_device 
> > > > > *dev, bool suspend,
> > > > >           if (r) {
> > > > >               /* delay GPU reset to resume */
> > > > >               radeon_fence_driver_force_completion(rdev, i);
> > > > > +        } else {
> > > > > +            /* finish executing delayed work */
> > > > > + flush_delayed_work(&rdev->fence_drv[i].lockup_work);
> > > > >           }
> > > > >       }