[PATCH 01/18] drm/i915/execlists: Assert tasklet is locked for process_csb()

[Chris Wilson]

We rely on only the tasklet being allowed to call into process_csb(), so
assert that is locked when we do. As the tasklet uses a simple bitlock,
there is no strong lockdep checking so we must make do with a plain
assertion that the tasklet is running and assume that we are the
tasklet!

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/gt/intel_lrc.c | 1 +
 drivers/gpu/drm/i915/i915_gem.h     | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 16b878d35814..fc4be76b3070 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1843,6 +1843,7 @@ static void process_csb(struct intel_engine_cs *engine)
 	u8 head, tail;
 
 	GEM_BUG_ON(USES_GUC_SUBMISSION(engine->i915));
+	GEM_BUG_ON(!tasklet_is_locked(&execlists->tasklet));
 
 	/*
 	 * Note that csb_write, csb_status may be either in HWSP or mmio.
diff --git a/drivers/gpu/drm/i915/i915_gem.h b/drivers/gpu/drm/i915/i915_gem.h
index db20d2b0842b..f6f9675848b8 100644
--- a/drivers/gpu/drm/i915/i915_gem.h
+++ b/drivers/gpu/drm/i915/i915_gem.h
@@ -86,6 +86,11 @@ static inline void tasklet_lock(struct tasklet_struct *t)
 		cpu_relax();
 }
 
+static inline bool tasklet_is_locked(const struct tasklet_struct *t)
+{
+	return test_bit(TASKLET_STATE_RUN, &t->state);
+}
+
 static inline void __tasklet_disable_sync_once(struct tasklet_struct *t)
 {
 	if (!atomic_fetch_inc(&t->count))
-- 
2.23.0