Re: [PATCH] accel/rocket: search every core slot when a core is removed

[Igor Paunovic]

Hi Sidong,

> I've tested this patch in Radxa Rock 5 B+ and it works.

Thank you. That is the first test of it on an RK3588 that is not mine, and
b4 collects your tag with the comment attached.

> It seems that there is other issue about num_core. For example,
> sched_to_core() finds core for sched with num_core and it could make
> same error like find_core_for_dev().

You were right, and it is worse than a failed lookup: neither caller checks
what sched_to_core() returns.

I built a KASAN kernel and unbound the middle of the three cores while three
clients were submitting to all of them. It faults twice, once from the
surviving core's job queue and once from its reset work:

  KASAN: null-ptr-deref in range [0x0000000000000220-0x0000000000000227]
  Workqueue: fdad0000.npu drm_sched_run_job_work [gpu_sched]
  pc : rocket_job_run+0x234/0x838 [rocket]

  KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
  Workqueue: rocket-reset-2 drm_sched_job_timedout [gpu_sched]
  pc : rocket_job_timedout+0xf0/0x1e0 [rocket]

Both are the third core. The workqueue names are its device and its
core->index, and it had been left at slot 2 while num_cores was down to 2.

The fix is one word, and it carries your Reported-by:

  https://lore.kernel.org/dri-devel/20260905150432.7477-1-royalnet026@xxxxxxxxx/

Same test on a kernel with it applied: no faults, journal clean. It applies
on top of the patch you tested, since max_cores comes from that one.

What it does not fix, and the patch says so: an open client keeps an entity
pointing at the scheduler of the core that went away. drm_sched then logs
"not ready, skipping" for every job that lands on it - 25006 of them in my
run - and the client waits in dma_fence_default_wait for a fence that will
never signal. The board stays up and the client hangs. Making one core of
several safe to unbind while a client is open needs more than a fix, and I
did not want to hide that behind a patch that only stops the oops.

Thanks for reading it closely enough to spot the second one.

Igor