drm/i915: Defer semaphore priority bumping to a workqueue

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]

Closes: https://gitlab.freedesktop.org/drm/intel/issues/1318
Fixes: c6b7bcbe100a ("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+
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200310101720.9944-1-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index fa65ec9e16f1838249273f9123d46539126d8c61..74169671afb5a794eee5f45a3a82f6c4d9e3d07c 100644 (file)
--- 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;
        }
 
@@ -1400,9 +1412,9 @@ 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 6020d5b2a3dfabe86685117d806a84dcdd8a0bbd..3c552bfea67a68eba098524687572250ce4f34e9 100644 (file)
--- 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.