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path: root/drivers/gpu/drm/i915/gt/intel_context.c
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Diffstat (limited to 'drivers/gpu/drm/i915/gt/intel_context.c')
-rw-r--r--drivers/gpu/drm/i915/gt/intel_context.c21
1 files changed, 17 insertions, 4 deletions
diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
index ee9d2bcd2c13..ef7bc41ffffa 100644
--- a/drivers/gpu/drm/i915/gt/intel_context.c
+++ b/drivers/gpu/drm/i915/gt/intel_context.c
@@ -310,10 +310,23 @@ int intel_context_prepare_remote_request(struct intel_context *ce,
GEM_BUG_ON(rq->hw_context == ce);
if (rcu_access_pointer(rq->timeline) != tl) { /* timeline sharing! */
- err = mutex_lock_interruptible_nested(&tl->mutex,
- SINGLE_DEPTH_NESTING);
- if (err)
- return err;
+ /*
+ * Ideally, we just want to insert our foreign fence as
+ * a barrier into the remove context, such that this operation
+ * occurs after all current operations in that context, and
+ * all future operations must occur after this.
+ *
+ * Currently, the timeline->last_request tracking is guarded
+ * by its mutex and so we must obtain that to atomically
+ * insert our barrier. However, since we already hold our
+ * timeline->mutex, we must be careful against potential
+ * inversion if we are the kernel_context as the remote context
+ * will itself poke at the kernel_context when it needs to
+ * unpin. Ergo, if already locked, we drop both locks and
+ * try again (through the magic of userspace repeating EAGAIN).
+ */
+ if (!mutex_trylock(&tl->mutex))
+ return -EAGAIN;
/* Queue this switch after current activity by this context. */
err = i915_active_fence_set(&tl->last_request, rq);