On 20/01/2023 23:28, John.C.Harrison@xxxxxxxxx wrote:
From: John Harrison <John.C.Harrison@xxxxxxxxx>
When GuC support was added to error capture, the locking around the
request object was broken. Fix it up.
The context based search manages the spinlocking around the search
internally. So it needs to grab the reference count internally as
well. The execlist only request based search relies on external
locking, so it needs an external reference count but within the
spinlock not outside it.
The only other caller of the context based search is the code for
dumping engine state to debugfs. That code wasn't previously getting
an explicit reference at all as it does everything while holding the
execlist specific spinlock. So, that needs updaing as well as that
spinlock doesn't help when using GuC submission. Rather than trying to
conditionally get/put depending on submission model, just change it to
always do the get/put.
In addition, intel_guc_find_hung_context() was not acquiring the
correct spinlock before searching the request list. So fix that up
too. While at it, add some extra whitespace padding for readability.
Is this part splittable into a separate patch?
v2: Explicitly document adding an extra blank line in some dense code
(Andy Shevchenko). Fix multiple potential null pointer derefs in case
of no request found (some spotted by Tvrtko, but there was more!).
Also fix a leaked request in case of !started and another in
__guc_reset_context now that intel_context_find_active_request is
actually reference counting the returned request.
v3: Add a _get suffix to intel_context_find_active_request now that it
grabs a reference (Daniele).
Fixes: dc0dad365c5e ("drm/i915/guc: Fix for error capture after full GPU reset with GuC")
Fixes: 573ba126aef3 ("drm/i915/guc: Capture error state on context reset")
Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
Cc: John Harrison <John.C.Harrison@xxxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
Cc: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Matt Roper <matthew.d.roper@xxxxxxxxx>
Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@xxxxxxxxx>
Cc: Michael Cheng <michael.cheng@xxxxxxxxx>
Cc: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
Cc: Tejas Upadhyay <tejaskumarx.surendrakumar.upadhyay@xxxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Aravind Iddamsetty <aravind.iddamsetty@xxxxxxxxx>
Cc: Alan Previn <alan.previn.teres.alexis@xxxxxxxxx>
Cc: Bruce Chang <yu.bruce.chang@xxxxxxxxx>
Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
---
drivers/gpu/drm/i915/gt/intel_context.c | 4 +++-
drivers/gpu/drm/i915/gt/intel_context.h | 3 +--
drivers/gpu/drm/i915/gt/intel_engine_cs.c | 6 +++++-
drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 14 +++++++++++++-
drivers/gpu/drm/i915/i915_gpu_error.c | 13 ++++++-------
5 files changed, 28 insertions(+), 12 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
index e94365b08f1ef..4285c1c71fa12 100644
--- a/drivers/gpu/drm/i915/gt/intel_context.c
+++ b/drivers/gpu/drm/i915/gt/intel_context.c
@@ -528,7 +528,7 @@ struct i915_request *intel_context_create_request(struct intel_context *ce)
return rq;
}
-struct i915_request *intel_context_find_active_request(struct intel_context *ce)
+struct i915_request *intel_context_find_active_request_get(struct intel_context *ce)
TBH I don't "dig" this name, it's a bit on the long side and feels out of character. I won't insist it be changed, but if get really has to be included in the name I would be happy with intel_context_get_active_request().
{
struct intel_context *parent = intel_context_to_parent(ce);
struct i915_request *rq, *active = NULL;
@@ -552,6 +552,8 @@ struct i915_request *intel_context_find_active_request(struct intel_context *ce)
active = rq;
}
+ if (active)
+ active = i915_request_get_rcu(active);
spin_unlock_irqrestore(&parent->guc_state.lock, flags);
return active;
diff --git a/drivers/gpu/drm/i915/gt/intel_context.h b/drivers/gpu/drm/i915/gt/intel_context.h
index fb62b7b8cbcda..ccc80c6607ca8 100644
--- a/drivers/gpu/drm/i915/gt/intel_context.h
+++ b/drivers/gpu/drm/i915/gt/intel_context.h
@@ -268,8 +268,7 @@ int intel_context_prepare_remote_request(struct intel_context *ce,
struct i915_request *intel_context_create_request(struct intel_context *ce);
-struct i915_request *
-intel_context_find_active_request(struct intel_context *ce);
+struct i915_request *intel_context_find_active_request_get(struct intel_context *ce);
static inline bool intel_context_is_barrier(const struct intel_context *ce)
{
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
index 922f1bb22dc68..fbc0a81617e89 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -2237,9 +2237,11 @@ static void engine_dump_active_requests(struct intel_engine_cs *engine, struct d
if (guc) {
ce = intel_engine_get_hung_context(engine);
if (ce)
- hung_rq = intel_context_find_active_request(ce);
+ hung_rq = intel_context_find_active_request_get(ce);
} else {
hung_rq = intel_engine_execlist_find_hung_request(engine);
+ if (hung_rq)
+ hung_rq = i915_request_get_rcu(hung_rq);
}
if (hung_rq)
@@ -2250,6 +2252,8 @@ static void engine_dump_active_requests(struct intel_engine_cs *engine, struct d
else
intel_engine_dump_active_requests(&engine->sched_engine->requests,
hung_rq, m);
+ if (hung_rq)
+ i915_request_put(hung_rq);
Argh... this is so horrible - not your patch - but the existing state of GuC backend was plugged in. I honestly don't know what to suggest here at this point... Above we have:
if (guc)
intel_guc_dump_active_requests(engine, hung_rq, m);
else
intel_engine_dump_active_requests(&engine->sched_engine->requests,
hung_rq, m);
As per your analysis the execlists code wants one lock held over that, especially when it calls intel_engine_dump_active_requests, which the GuC backed will also call from intel_guc_dump_active_requests (!) just needs a different lock held around it.
Is the lock held by intel_engine_dump over the call to engine_dump_active_requests truly useless in case of GuC? Or just wrong scope (too wide)?
}
void intel_engine_dump(struct intel_engine_cs *engine,
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index b436dd7f12e42..ad4b2848b0f83 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -1702,7 +1702,7 @@ static void __guc_reset_context(struct intel_context *ce, intel_engine_mask_t st
goto next_context;
guilty = false;
- rq = intel_context_find_active_request(ce);
+ rq = intel_context_find_active_request_get(ce);
if (!rq) {
head = ce->ring->tail;
goto out_replay;
@@ -1715,6 +1715,7 @@ static void __guc_reset_context(struct intel_context *ce, intel_engine_mask_t st
head = intel_ring_wrap(ce->ring, rq->head);
__i915_request_reset(rq, guilty);
+ i915_request_put(rq);
out_replay:
guc_reset_state(ce, head, guilty);
next_context:
@@ -4820,6 +4821,8 @@ void intel_guc_find_hung_context(struct intel_engine_cs *engine)
xa_lock_irqsave(&guc->context_lookup, flags);
xa_for_each(&guc->context_lookup, index, ce) {
+ bool found;
+
if (!kref_get_unless_zero(&ce->ref))
continue;
@@ -4836,10 +4839,18 @@ void intel_guc_find_hung_context(struct intel_engine_cs *engine)
goto next;
}
+ found = false;
+ spin_lock(&ce->guc_state.lock);
list_for_each_entry(rq, &ce->guc_state.requests, sched.link) {
if (i915_test_request_state(rq) != I915_REQUEST_ACTIVE)
continue;
+ found = true;
+ break;
+ }
+ spin_unlock(&ce->guc_state.lock);
+
+ if (found) {
intel_engine_set_hung_context(engine, ce);
/* Can only cope with one hang at a time... */
@@ -4847,6 +4858,7 @@ void intel_guc_find_hung_context(struct intel_engine_cs *engine)
xa_lock(&guc->context_lookup);
goto done;
}
+
next:
intel_context_put(ce);
xa_lock(&guc->context_lookup);
diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 9d5d5a397b64e..5c73dfa2fb3f6 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -1607,7 +1607,7 @@ capture_engine(struct intel_engine_cs *engine,
ce = intel_engine_get_hung_context(engine);
if (ce) {
intel_engine_clear_hung_context(engine);
- rq = intel_context_find_active_request(ce);
+ rq = intel_context_find_active_request_get(ce);
if (!rq || !i915_request_started(rq))
goto no_request_capture;
} else {
@@ -1618,21 +1618,18 @@ capture_engine(struct intel_engine_cs *engine,
if (!intel_uc_uses_guc_submission(&engine->gt->uc)) {
spin_lock_irqsave(&engine->sched_engine->lock, flags);
rq = intel_engine_execlist_find_hung_request(engine);
+ if (rq)
+ rq = i915_request_get_rcu(rq);
spin_unlock_irqrestore(&engine->sched_engine->lock,
flags);
Is it possible to consolidate this block with the one in engine_dump_active_requests? They seem identical..
guc = intel_uc_uses_guc_submission(&engine->gt->uc);
if (guc) {
ce = intel_engine_get_hung_context(engine);
if (ce)
hung_rq = intel_context_find_active_request(ce);
} else {
hung_rq = intel_engine_execlist_find_hung_request(engine);
}
vs
ce = intel_engine_get_hung_context(engine);
if (ce) {
intel_engine_clear_hung_context(engine);
rq = intel_context_find_active_request(ce);
if (!rq || !i915_request_started(rq))
goto no_request_capture;
} else {
/*
* Getting here with GuC enabled means it is a forced error capture
* with no actual hang. So, no need to attempt the execlist search.
*/
if (!intel_uc_uses_guc_submission(&engine->gt->uc)) {
spin_lock_irqsave(&engine->sched_engine->lock, flags);
rq = intel_engine_execlist_find_hung_request(engine);
spin_unlock_irqrestore(&engine->sched_engine->lock,
flags);
}
}
We'd need a backend agnostic helper like:
intel_engine_get_hung_request(...)
{
...
guc = intel_uc_uses_guc_submission(&engine->gt->uc);
if (guc) {
ce = intel_engine_get_hung_context(engine);
if (ce)
hung_rq = intel_context_find_active_request(ce);
} else {
hung_rq = intel_engine_execlist_find_hung_request(engine);
}
If locking can be untangled to work correctly for both callers.
Looks like I can't do a quick review on this but need to set aside a larger chunk of time. I'll try tomorrow.
Regards,
Tvrtko
}
}
- if (rq)
- rq = i915_request_get_rcu(rq);
-
if (!rq)
goto no_request_capture;
capture = intel_engine_coredump_add_request(ee, rq, ATOMIC_MAYFAIL);
- if (!capture) {
- i915_request_put(rq);
+ if (!capture)
goto no_request_capture;
- }
if (dump_flags & CORE_DUMP_FLAG_IS_GUC_CAPTURE)
intel_guc_capture_get_matching_node(engine->gt, ee, ce);
@@ -1642,6 +1639,8 @@ capture_engine(struct intel_engine_cs *engine,
return ee;
no_request_capture:
+ if (rq)
+ i915_request_put(rq);
kfree(ee);
return NULL;
}
