The function intel_engine_breadcrumbs_irq() is always invoked from an interrupt handler and for that reason it invokes (as an optimisation) only spin_lock() for locking assuming that the interrupts are already disabled. The function intel_engine_signal_breadcrumbs() is provided to disable interrupts while the former function is invoked so that assumption is also true for callers from preemptible context.

On PREEMPT_RT local_irq_disable() really disables interrupts and this forbids to invoke spin_lock() which becomes a sleeping spinlock.

This is also problematic with `threadirqs' in conjunction with irq_work. With force threading the interrupt handler, the handler is invoked with disabled BH but with interrupts enabled. This is okay and the lock itself is never acquired in IRQ context. This changes with irq_work (signal_irq_work()) which _still_ invokes intel_engine_breadcrumbs_irq() from IRQ context. Lockdep should see this and complain.

Acquire the locks in intel_engine_breadcrumbs_irq() with _irqsave() suffix and let all callers invoke intel_engine_breadcrumbs_irq() directly instead using intel_engine_signal_breadcrumbs().

Reported-by: Clark Williams williams@redhat.com Signed-off-by: Sebastian Andrzej Siewior bigeasy@linutronix.de --- drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 16 +++++----------- drivers/gpu/drm/i915/gt/intel_engine.h | 1 - drivers/gpu/drm/i915/gt/intel_hangcheck.c | 2 +- drivers/gpu/drm/i915/gt/intel_reset.c | 2 +- 4 files changed, 7 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c index 09c68dda20988..f750375056de4 100644 --- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c +++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c @@ -134,9 +134,10 @@ void intel_engine_breadcrumbs_irq(struct intel_engine_cs *engine) const ktime_t timestamp = ktime_get(); struct intel_context *ce, *cn; struct list_head *pos, *next; + unsigned long flags; LIST_HEAD(signal);

- spin_lock(&b->irq_lock); + spin_lock_irqsave(&b->irq_lock, flags);

if (b->irq_armed && list_empty(&b->signalers)) __intel_breadcrumbs_disarm_irq(b); @@ -182,30 +183,23 @@ void intel_engine_breadcrumbs_irq(struct intel_engine_cs *engine) } }

- spin_unlock(&b->irq_lock); + spin_unlock_irqrestore(&b->irq_lock, flags);

list_for_each_safe(pos, next, &signal) { struct i915_request *rq = list_entry(pos, typeof(*rq), signal_link); struct list_head cb_list;

- spin_lock(&rq->lock); + spin_lock_irqsave(&rq->lock, flags); list_replace(&rq->fence.cb_list, &cb_list); __dma_fence_signal__timestamp(&rq->fence, timestamp); __dma_fence_signal__notify(&rq->fence, &cb_list); - spin_unlock(&rq->lock); + spin_unlock_irqrestore(&rq->lock, flags);

i915_request_put(rq); } }

-void intel_engine_signal_breadcrumbs(struct intel_engine_cs *engine) -{ - local_irq_disable(); - intel_engine_breadcrumbs_irq(engine); - local_irq_enable(); -} - static void signal_irq_work(struct irq_work *work) { struct intel_engine_cs *engine = diff --git a/drivers/gpu/drm/i915/gt/intel_engine.h b/drivers/gpu/drm/i915/gt/intel_engine.h index d3c6993f4f46f..c9e8c8ccbd47f 100644 --- a/drivers/gpu/drm/i915/gt/intel_engine.h +++ b/drivers/gpu/drm/i915/gt/intel_engine.h @@ -335,7 +335,6 @@ void intel_engine_init_execlists(struct intel_engine_cs *engine); void intel_engine_init_breadcrumbs(struct intel_engine_cs *engine); void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine);

-void intel_engine_signal_breadcrumbs(struct intel_engine_cs *engine); void intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine);

static inline void diff --git a/drivers/gpu/drm/i915/gt/intel_hangcheck.c b/drivers/gpu/drm/i915/gt/intel_hangcheck.c index 05d042cdefe24..7ca67aac27d4d 100644 --- a/drivers/gpu/drm/i915/gt/intel_hangcheck.c +++ b/drivers/gpu/drm/i915/gt/intel_hangcheck.c @@ -283,7 +283,7 @@ static void hangcheck_elapsed(struct work_struct *work) for_each_engine(engine, gt->i915, id) { struct hangcheck hc;

- intel_engine_signal_breadcrumbs(engine); + intel_engine_breadcrumbs_irq(engine);

hangcheck_load_sample(engine, &hc); hangcheck_accumulate_sample(engine, &hc); diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c b/drivers/gpu/drm/i915/gt/intel_reset.c index b9d84d52e9864..1d5497a58eeb1 100644 --- a/drivers/gpu/drm/i915/gt/intel_reset.c +++ b/drivers/gpu/drm/i915/gt/intel_reset.c @@ -697,7 +697,7 @@ static void reset_finish_engine(struct intel_engine_cs *engine) engine->reset.finish(engine); intel_uncore_forcewake_put(engine->uncore, FORCEWAKE_ALL);

- intel_engine_signal_breadcrumbs(engine); + intel_engine_breadcrumbs_irq(engine); }

static void reset_finish(struct intel_gt *gt, intel_engine_mask_t awake)

The lockdep_assert_irqs_disabled() check is needless. The previous lockdep_assert_held() check ensures that the lock is acquired and while the lock is acquired lockdep also prints a warning if the interrupts are not disabled if they have to be. These IRQ-off asserts trigger on PREEMPT_RT because the locks become sleeping locks and do not really disable interrupts.

Remove lockdep_assert_irqs_disabled().

Reported-by: Clark Williams williams@redhat.com Signed-off-by: Sebastian Andrzej Siewior bigeasy@linutronix.de --- drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 3 --- 1 file changed, 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c index f750375056de4..55317081d48b0 100644 --- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c +++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c @@ -120,7 +120,6 @@ __dma_fence_signal__notify(struct dma_fence *fence, struct dma_fence_cb *cur, *tmp;

lockdep_assert_held(fence->lock); - lockdep_assert_irqs_disabled();

list_for_each_entry_safe(cur, tmp, list, node) { INIT_LIST_HEAD(&cur->node); @@ -269,7 +268,6 @@ void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine) bool i915_request_enable_breadcrumb(struct i915_request *rq) { lockdep_assert_held(&rq->lock); - lockdep_assert_irqs_disabled();

if (test_bit(I915_FENCE_FLAG_ACTIVE, &rq->fence.flags)) { struct intel_breadcrumbs *b = &rq->engine->breadcrumbs; @@ -319,7 +317,6 @@ void i915_request_cancel_breadcrumb(struct i915_request *rq) struct intel_breadcrumbs *b = &rq->engine->breadcrumbs;

lockdep_assert_held(&rq->lock); - lockdep_assert_irqs_disabled();

/* * We must wait for b->irq_lock so that we know the interrupt handler