On 1/31/2024 10:48, Janusz Krzysztofik wrote:
Hi John,
On Wednesday, 10 January 2024 22:02:16 CET John.C.Harrison@xxxxxxxxx wrote:
From: John Harrison <John.C.Harrison@xxxxxxxxx>
The context persistence code does things like send super high priority
heartbeat pulses to ensure any leaked context can still be pre-empted
and thus isn't a total denial of service but only a minor denial of
service. Unfortunately, it wasn't bothering to restart the heatbeat
worker with a fresh timeout. Thus, if a persistent context happened to
be closed just before the heartbeat was going to go ping anyway then
the forced pulse would get a negligble execution time. And as the
forced pulse is super high priority, the worker thread's next step is
a reset. Which means a potentially innocent system randomly goes boom
when attempting to close a context. So, force a re-schedule of the
worker thread with the appropriate timeout.
I haven't looked too much in heartbeat pulses code before, but I think I can
understand your change. I've also got a positive opinion from Chris on it.
I can provide my Ack, assuming the pre-merge failure reported by CI is not
related, but could you please comment that failure first and/or ask BUG Filing
to handle it so we have it cleaned up?
Pretty confident the CI failure is unrelated. Not seeing how a change to
the heartbeat timing of persistence context clean up could cause a HDMI
test to fail to complete.
However, I was really hoping for a full code review by someone who
understands this code and would be able to say whether there could be
unexpected side effects of the change. Or even if there is a better /
safer way to fix the problem.
@Andi Shyti, you were fingered as being someone who might have such
knowledge. Can you comment?
Thanks,
John.
Thanks,
Janusz
Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
---
drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c b/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c
index 1a8e2b7db0138..4ae2fa0b61dd4 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c
@@ -290,6 +290,9 @@ static int __intel_engine_pulse(struct intel_engine_cs *engine)
heartbeat_commit(rq, &attr);
GEM_BUG_ON(rq->sched.attr.priority < I915_PRIORITY_BARRIER);
+ /* Ensure the forced pulse gets a full period to execute */
+ next_heartbeat(engine);
+
return 0;
}
