drm/i915: Lock the gem_context->active_list while dropping the link

On unpinning the intel_context, we remove it from the active list
inside the GEM context. This list is supposed to be guarded by the GEM
context mutex, so remember to take it!

Fixes: 7e3d9a59410d ("drm/i915: Track active engines within a context")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190318212347.30146-1-chris@chris-wilson.co.uk

1 files changed, 11 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/intel_context.c b/drivers/gpu/drm/i915/intel_context.c
index 5a16c9bb2778..0ab894a058f6 100644
--- a/drivers/gpu/drm/i915/intel_context.c
+++ b/drivers/gpu/drm/i915/intel_context.c
@@ -165,13 +165,13 @@ intel_context_pin(struct i915_gem_context *ctx,
 		if (err)
 			goto err;
 
+		i915_gem_context_get(ctx);
+		GEM_BUG_ON(ce->gem_context != ctx);
+
 		mutex_lock(&ctx->mutex);
 		list_add(&ce->active_link, &ctx->active_engines);
 		mutex_unlock(&ctx->mutex);
 
-		i915_gem_context_get(ctx);
-		GEM_BUG_ON(ce->gem_context != ctx);
-
 		smp_mb__before_atomic(); /* flush pin before it is visible */
 	}
 
@@ -194,9 +194,16 @@ void intel_context_unpin(struct intel_context *ce)
 	/* We may be called from inside intel_context_pin() to evict another */
 	mutex_lock_nested(&ce->pin_mutex, SINGLE_DEPTH_NESTING);
 
-	if (likely(atomic_dec_and_test(&ce->pin_count)))
+	if (likely(atomic_dec_and_test(&ce->pin_count))) {
 		ce->ops->unpin(ce);
 
+		mutex_lock(&ce->gem_context->mutex);
+		list_del(&ce->active_link);
+		mutex_unlock(&ce->gem_context->mutex);
+
+		i915_gem_context_put(ce->gem_context);
+	}
+
 	mutex_unlock(&ce->pin_mutex);
 }