drm/i915: Pin the context as we work on it

Since we now allow the intel_context_unpin() to run unserialised, we
risk our operations under the intel_context_lock_pinned() being run as
the context is unpinned (and thus invalidating our state). We can
atomically acquire the pin, testing to see if it is pinned in the
process, thus ensuring that the state remains consistent during the
course of the whole operation.

Fixes: 841350223816 ("drm/i915/gt: Drop mutex serialisation between context pin/unpin")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200109085142.871563-1-chris@chris-wilson.co.uk

1 files changed, 7 insertions, 3 deletions

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
index 88f6253f5405..a2e57e62af30 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
@@ -1236,12 +1236,14 @@ gen8_modify_rpcs(struct intel_context *ce, struct intel_sseu sseu)
 	 * image, or into the registers directory, does not stick). Pristine
 	 * and idle contexts will be configured on pinning.
 	 */
-	if (!intel_context_is_pinned(ce))
+	if (!intel_context_pin_if_active(ce))
 		return 0;
 
 	rq = intel_engine_create_kernel_request(ce->engine);
-	if (IS_ERR(rq))
-		return PTR_ERR(rq);
+	if (IS_ERR(rq)) {
+		ret = PTR_ERR(rq);
+		goto out_unpin;
+	}
 
 	/* Serialise with the remote context */
 	ret = intel_context_prepare_remote_request(ce, rq);
@@ -1249,6 +1251,8 @@ gen8_modify_rpcs(struct intel_context *ce, struct intel_sseu sseu)
 		ret = gen8_emit_rpcs_config(rq, ce, sseu);
 
 	i915_request_add(rq);
+out_unpin:
+	intel_context_unpin(ce);
 	return ret;
 }