On 10/03/2020 10:17, Chris Wilson wrote:

Since the semaphore fence may be signaled from inside an interrupt handler from inside a request holding its request->lock, we cannot then enter into the engine->active.lock for processing the semaphore priority bump as we may traverse our call tree and end up on another held request.

CPU 0: [ 2243.218864] _raw_spin_lock_irqsave+0x9a/0xb0 [ 2243.218867] i915_schedule_bump_priority+0x49/0x80 [i915] [ 2243.218869] semaphore_notify+0x6d/0x98 [i915] [ 2243.218871] __i915_sw_fence_complete+0x61/0x420 [i915] [ 2243.218874] ? kmem_cache_free+0x211/0x290 [ 2243.218876] i915_sw_fence_complete+0x58/0x80 [i915] [ 2243.218879] dma_i915_sw_fence_wake+0x3e/0x80 [i915] [ 2243.218881] signal_irq_work+0x571/0x690 [i915] [ 2243.218883] irq_work_run_list+0xd7/0x120 [ 2243.218885] irq_work_run+0x1d/0x50 [ 2243.218887] smp_irq_work_interrupt+0x21/0x30 [ 2243.218889] irq_work_interrupt+0xf/0x20

CPU 1: [ 2242.173107] _raw_spin_lock+0x8f/0xa0 [ 2242.173110] __i915_request_submit+0x64/0x4a0 [i915] [ 2242.173112] __execlists_submission_tasklet+0x8ee/0x2120 [i915] [ 2242.173114] ? i915_sched_lookup_priolist+0x1e3/0x2b0 [i915] [ 2242.173117] execlists_submit_request+0x2e8/0x2f0 [i915] [ 2242.173119] submit_notify+0x8f/0xc0 [i915] [ 2242.173121] __i915_sw_fence_complete+0x61/0x420 [i915] [ 2242.173124] ? _raw_spin_unlock_irqrestore+0x39/0x40 [ 2242.173137] i915_sw_fence_complete+0x58/0x80 [i915] [ 2242.173140] i915_sw_fence_commit+0x16/0x20 [i915]

CPU 2: [ 2242.173107] _raw_spin_lock+0x8f/0xa0 [ 2242.173110] __i915_request_submit+0x64/0x4a0 [i915] [ 2242.173112] __execlists_submission_tasklet+0x8ee/0x2120 [i915] [ 2242.173114] ? i915_sched_lookup_priolist+0x1e3/0x2b0 [i915] [ 2242.173117] execlists_submit_request+0x2e8/0x2f0 [i915] [ 2242.173119] submit_notify+0x8f/0xc0 [i915]

Closes: https://gitlab.freedesktop.org/drm/intel/issues/1318 Fixes: b7404c7ecb38 ("drm/i915: Bump ready tasks ahead of busywaits") Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Tvrtko Ursulin tvrtko.ursulin@intel.com Cc: stable@vger.kernel.org # v5.2+

---

drivers/gpu/drm/i915/i915_request.c | 22 +++++++++++++++++----- drivers/gpu/drm/i915/i915_request.h | 2 ++ 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index 04b52bf347bf..129357d4b599 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -588,19 +588,31 @@ submit_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify state) return NOTIFY_DONE; } +static void irq_semaphore_cb(struct irq_work *wrk) +{

• struct i915_request *rq =

• container_of(wrk, typeof(*rq), semaphore_work);
  

• i915_schedule_bump_priority(rq, I915_PRIORITY_NOSEMAPHORE);
• i915_request_put(rq);

+}

• static int __i915_sw_fence_call semaphore_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify state) {

• struct i915_request *request =

• container_of(fence, typeof(*request), semaphore);
  

• struct i915_request *rq = container_of(fence, typeof(*rq), semaphore);

switch (state) { case FENCE_COMPLETE:

• i915_schedule_bump_priority(request, I915_PRIORITY_NOSEMAPHORE);
  

• if (!(READ_ONCE(rq->sched.attr.priority) & I915_PRIORITY_NOSEMAPHORE)) {
  

• 	i915_request_get(rq);
  

• 	init_irq_work(&rq->semaphore_work, irq_semaphore_cb);
  

• 	irq_work_queue(&rq->semaphore_work);
  

• }
  

  break;

case FENCE_FREE:

• i915_request_put(request);
  

• i915_request_put(rq);
  

  break; }

@@ -1369,9 +1381,9 @@ void __i915_request_queue(struct i915_request *rq, * decide whether to preempt the entire chain so that it is ready to * run at the earliest possible convenience. */

• i915_sw_fence_commit(&rq->semaphore); if (attr && rq->engine->schedule) rq->engine->schedule(rq, attr);

• i915_sw_fence_commit(&rq->semaphore); i915_sw_fence_commit(&rq->submit); }

diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h index 6020d5b2a3df..3c552bfea67a 100644 --- a/drivers/gpu/drm/i915/i915_request.h +++ b/drivers/gpu/drm/i915/i915_request.h @@ -26,6 +26,7 @@ #define I915_REQUEST_H #include <linux/dma-fence.h> +#include <linux/irq_work.h> #include <linux/lockdep.h> #include "gem/i915_gem_context_types.h" @@ -208,6 +209,7 @@ struct i915_request { }; struct list_head execute_cb; struct i915_sw_fence semaphore;

• struct irq_work semaphore_work;

/* * A list of everyone we wait upon, and everyone who waits upon us.

Reviewed-by: Tvrtko Ursulin tvrtko.ursulin@intel.com

Regards,

Tvrtko