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Subject[PATCH 5.5 088/151] drm/i915: Defer semaphore priority bumping to a workqueue
Date
From: Chris Wilson <chris@chris-wilson.co.uk>

commit 14a0d527a479eb2cb6067f9e5e163e1bf35db2a9 upstream.

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: 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+
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200310101720.9944-1-chris@chris-wilson.co.uk
(cherry picked from commit 209df10bb4536c81c2540df96c02cd079435357f)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -529,19 +529,31 @@ submit_notify(struct i915_sw_fence *fenc
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;
}

@@ -1283,9 +1295,9 @@ void __i915_request_queue(struct i915_re
* 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);
}

--- 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 "gt/intel_context_types.h"
@@ -147,6 +148,7 @@ 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.

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