[PATCH 5/6] drm/i915: Wrap engine->schedule in RCU locks for set-wedge protection

Chris Wilson
2018-03-07T13:42:49Z

Similar to the staging around handling of engine->submit_request, we
need to stop adding to the execlists->queue prior to calling
engine->cancel_requests. cancel_requests will move requests from the
queue onto the timeline, so if we add a request onto the queue after that
point, it will be lost.

Fixes: af7a8ffad9c5 ("drm/i915: Use rcu instead of stop_machine in set_wedged")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
---
drivers/gpu/drm/i915/i915_gem.c | 13 +++++++------
drivers/gpu/drm/i915/i915_request.c | 2 ++
2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 30cd07ebcb8e..3b44952e089f 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -471,10 +471,11 @@ static void __fence_set_priority(struct dma_fence *fence, int prio)

rq = to_request(fence);
engine = rq->engine;
- if (!engine->schedule)
- return;

- engine->schedule(rq, prio);
+ rcu_read_lock();
+ if (engine->schedule)
+ engine->schedule(rq, prio);
+ rcu_read_unlock();
}

static void fence_set_priority(struct dma_fence *fence, int prio)
@@ -3214,8 +3215,11 @@ void i915_gem_set_wedged(struct drm_i915_private *i915)
*/
for_each_engine(engine, i915, id) {
i915_gem_reset_prepare_engine(engine);
+
engine->submit_request = nop_submit_request;
+ engine->schedule = NULL;
}
+ i915->caps.scheduler = 0;

/*
* Make sure no one is running the old callback before we proceed with
@@ -3233,11 +3237,8 @@ void i915_gem_set_wedged(struct drm_i915_private *i915)
* start to complete all requests.
*/
engine->submit_request = nop_complete_submit_request;
- engine->schedule = NULL;
}

- i915->caps.scheduler = 0;
-
/*
* Make sure no request can slip through without getting completed by
* either this call here to intel_engine_init_global_seqno, or the one
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 69b378a323fc..0258449579f8 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -1082,8 +1082,10 @@ void __i915_request_add(struct i915_request *request, bool flush_caches)
* decide whether to preempt the entire chain so that it is ready to
* run at the earliest possible convenience.
*/
+ rcu_read_lock();
if (engine->schedule)
engine->schedule(request, request->ctx->priority);
+ rcu_read_unlock();

local_bh_disable();
i915_sw_fence_commit(&request->submit);
--
2.16.2